Environ Sci Pollut Res DOI 10.1007/s11356-015-4307-z
REVIEW ARTICLE
Arsenic removal by nanoparticles: a review Mirna Habuda-Stanić & Marija Nujić
Received: 19 November 2014 / Accepted: 2 March 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract Contamination of natural waters with arsenic, which is both toxic and carcinogenic, is widespread. Among various technologies that have been employed for arsenic removal from water, such as coagulation, filtration, membrane separation, ion exchange, etc., adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities, and generally lower operation cost, but the need for technological innovation for water purification is gaining attention worldwide. Nanotechnology is considered to play a crucial role in providing clean and affordable water to meet human demands. This review presents an overview of nanoparticles and nanobased adsorbents and its efficiencies in arsenic removal from water. The paper highlights the application of nanomaterials and their properties, mechanisms, and advantages over conventional adsorbents for arsenic removal from contaminated water. Keywords Arsenic . Adsorption . Nanoparticles . Nanobased adsorbents . Water purification
Introduction Arsenic is a ubiquitous element in the environment. Because of its prevalence in nature and its toxicity, the potential for Responsible editor: Philippe Garrigues M. Habuda-Stanić (*) : M. Nujić Josip Juraj Strossmayer University of Osijek, Faculty of Food Technology Osijek, Mirna Habuda-Stanić, Franje Kuhača 20, 31000 Osijek, Croatia e-mail:
[email protected] M. Nujić e-mail:
[email protected]
arsenic contamination of water, air, and soil from both geological and anthropogenic sources is a significant environmental health concern (Smedley and Kinniburg 2002; Ng et al 2003). Elevated concentrations in surface water and groundwater of up to 100–5000 μg L−1 can be found in areas of sulfide mineralization (WHO 2001). A high amount of arsenic in groundwater was also reported in southeastern Asia (Bangladesh, India, China, Taiwan, Philippines), North and South America, and some parts of Europe (Hungary, Romania, Croatia, and Serbia) (Smedley and Kinniburg 2002; Ng et al 2003; WHO 2001, 2011; Gebel 1999; Ćavar et al. 2005; Romić et al. 2011; Rowland et al. 2011). Long-term exposure to arsenic has been associated with skin, lung, bladder, urinary tract, kidney, and liver cancer and other noncancerous illnesses. Consequently, in 1993, the World Health Organization (WHO) has revised the guideline for drinking water quality in which the concentration of arsenic was reduced from 50 down to 10 μg L−1 in order to minimize the harmful effects of arsenic on health. A wide range of arsenic toxicity has been determined. Generally, inorganic arsenic species (dimethylarsinate—DMA and monomethylarsonate—MMA) are more toxic than organic forms to living organisms, while As(III) is about 60 times more toxic than ionized As(V). Briefly, the toxicity of different arsenic species varies in order: arsenite > arsenate > MMA>DMA (Jain and Ali 2000). Inorganic arsenic in water can be present in nonionic trivalent form [As(III)] and ionic pentavalent [As(V)] forms, depending on the pH and redox potential. Under reducing conditions, such as aquifers with near neutral pH, trivalent nonionized arsenite as H3AsO3 is the dominant arsenic specie. Under an oxidizing environment and pH above neutral pH, dominant is the negatively charged pentavalent arsenate form. It is a well-known fact that ionized arsenate forms react easier and always effectively removed due to charged form in all known arsenic removal techniques (Smedley and Kinniburg
Environ Sci Pollut Res
2002; Sharma and Sohn 2009; van Halem 2011). Inorganic arsenic in water is mainly present in nonionic trivalent [As(III)] and ionic pentavalent [As(V)] forms in different proportions depending on the environmental conditions of the aquifer (Jain and Ali 2000; Sharma and Sohn 2009). It is well known that As(III) is more toxic and more difficult to remove from water than As(V) (WHO 2001; Smedley and Kinniburg 2002). Thus, preoxidation of As(III) to As(V) is required prior to adsorption, precipitation, or ion exchange process in order to achieve a higher removal effect (Sharma and Sohn 2009; Korte and Fernando 1991; Guan et al. 2009). Various technologies have been employed for arsenic removal from water, and the effectiveness of these technologies depends on the physical and chemical characteristic of the arsenic compounds in water. Arsenic is most effectively removed or stabilized when it is present in the arsenate form (Jekel 1994). The technologies for arsenic removal usually include the following processes: coagulation-filtration (Khan et al. 2002; Wickramasinghe et al. 2004; Bilici Baskan and Pala 2010; Mólgora et al. 2013), membrane separation (Ning 2002; Shih 2005; Pal et al. 2014), ion exchange (Flicklin 1983; Katsoyiannis and Zouboulis 2002; Tresintsi et al. 2014), and adsorption (Lin and Wu 2001; Zeng 2003; Chammui et al. 2014). Among these methods, adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities, and generally lower operation cost (Akin et al. 2012). Mohan and Pittman Jr. (2007) reviewed the most utilized arsenic removal techniques and summarized commercially available carbons. In the adsorption-based arsenic removal methods, many studies examined arsenic removal using activated alumina and various iron oxides/hydroxides as the adsorption media. Although these technologies and novel materials for selective adsorption of arsenic are effective, there are one or more limitations of application. Some of these limitations are related with the description of the surface complex’s structures and the types of reactive sites (Katsoyiannis and Zouboulis 2002) as well as the production of a large amount of sludge with a substantial concentration of arsenic (i.e., in coagulation/flocculation process) (Modal et al. 2013). Additionally, Xu et al. (2012) emphasized that the separation of nanomaterials after the water treatment process is expensive regarding time and chemicals used. Moreover, current water and wastewater treatment technologies and infrastructure are reaching their limit for providing adequate water quality to meet human and environmental needs (Pillewan et al. 2011; Qu et al. 2013a). Characteristics such as large surface area, high specificity, high reactivity, and catalytic potential make nanoparticles excellent candidates for water treatment applications (Hristovski et al. 2007; Qu et al. 2013b). Nanomaterials are also characterized by the potential for self-assembly, i.e., self-assembled monolayer on mesoporous supports. In addition, some nanomaterials (nanoalumina,
Ag or TiO2 nanoparticles) have been incorporated on a membrane surface by self-assembly to inactivate microorganisms or to prevent biofouling by releasing biocides (Qu et al. 2013b). Therefore, new demands are focused on developing specially designed tailor-made adsorbents for selective removal of arsenic from drinking water having equal affinity for As(III) and As(V), especially addressing the issue of safe disposal (Pillewan et al. 2011). However, the nanoparticles without a stabilizer or surface modifier tend to agglomerate rapidly into micron-scale or larger aggregates, thereby greatly diminishing the specific surface area and As sorption capacity. Therefore, to prevent particle agglomeration, stabilizers such as starch and carboxymethyl cellulose have been found to be effective in facilitating size control of various metal and metal oxide-based nanoparticles (An and Zhao 2012; Liang et al. 2013). However, the use of stabilizers can often enable the particles to be fully dispersible in water (An and Zhao 2012). Among the most widely used nanoparticles, magnetic nanoparticles, mainly nano-zerovalent iron (nZVI), magnetite (Fe3O4), and maghemite (γ-Fe2O3) nanoparticles, have attracted significant interest in research for engineering applications for the treatment of contaminated water (Yantasee et al. 2007; Li et al. 2012a; Tang et al. 2013; Song et al. 2013). Moreover, bimetallic combination (Fe0/Ni0) showed greater degradation rate: as iron corrodes, protons from water are reduced to adsorbed H atoms and to molecular hydrogen at the catalytic Ni surface (Khin et al. 2012). To overcome arsenic toxicity, which has become a major concern worldwide, it is necessary to develop the technology with improved materials and systems with high efficiency (Qu et al. 2013a; Shwe et al. 2012). Environmental nanotechnologies for the treatment of arsenic have been attracting increasing attention in the last few years. Although the area of nanoscience is relatively new, nanotechnology will play an essential role in the development of novel arsenic treatment process (Jing and Meng 2009); moreover, nanomaterials are drivers of the nanotechnology revolution (Savage and Diallo 2005). Thus, a key factor for the applications of nanotechnology to water purification will be the availability of suppliers that can provide large quantities of nanomaterials at economically acceptable prices (Prasse and Ternes 2010) (Fig. 1). This review presents the performances and adsorption capacities of various nanoparticles and nanobased adsorbents for arsenic removal from aqueous solutions (groundwater, drinking water, and wastewater). Arsenic removal using metal, metal oxides, and mixed metal nanoparticles, as well as some commercially available and low-cost nanoparticle-impregnated adsorbents, nanotubes, and various nanocomposites, mostly tested via bench studies, is surveyed, and most of their characteristics are summarized in an extensive table (Table 1). However, it has to be pointed out that facts such as a size-dependent toxicity of nanoparticles (Chen et al.
Environ Sci Pollut Res Fig. 1 Relevant processes for the removal of organic and inorganic pollutants from water (Prasse and Ternes 2010)
2011), the potential impact on human health, and issue of their disposal in environment, although very important, are not discussed in this review.
Application of nanoparticles on arsenic removal from water by adsorption Adsorption is a commonly used method for the removal of organic substances and inorganic contaminants in water and wastewater treatment. The effectiveness of conventional adsorbents is usually confined by the surface area or active sites, lack of selectivity, and adsorption kinetics. Usually, adsorption of arsenic on nano-adsorbents occurs in the following steps: (1) the adsorbate molecule is transported to the adsorbent surface by diffusion through the boundary layer, (2) the adsorbate diffuses from the external surface into the pores of the adsorbent, and (3) the adsorbate binds on the active sites of the internal pores (Malana et al. 2011). On the other side, when TiO2 is used, it oxidizes As(III) to As(V) in the presence of proper light, and finally, the sequent As(V) complexes with a metal oxide (Yamani et al. 2012). Nano-adsorbents offer significant improvement with their high specific surface area and sorption sites (Qu et al. 2013a, b). According to Liang et al. (2013), for water treatment, two features of nanoparticles are desired: (1) the particles should offer a high sorption capacity and (2) the spent particles should be amenable to easy separation from water and must not cause any harmful effects on the treated water. Results of some studies indicated that some ions (phosphate, carbonate, and bicarbonate) can inhibit arsenic adsorption or increase arsenic leaching from the adsorbent (Sharma and Sohn 2009). The influence of pH of nanoparticle leaching was also investigated and significant leaching from nanomaterials at higher acidic environment was reported (Matei et al. 2011).
Titanium-based nanoparticles Due to its low toxicity, chemical stability, and low cost, TiO2 is the most used semiconductor photocatalyst in water or wastewater treatment (Qu et al. 2013a). With UV light or sunlight irradiation, TiO2 functions as both, photocatalyst and adsorbent, while without irradiation, TiO2 works as adsorbent only (Guan et al. 2012). TiO2 photocatalysts effectively produce reactive oxygen species (ROS), especially superoxide and hydroxyl radicals, under UV-A irradiation, which enables activation by sunlight. ROS degrade organic contaminants and inactivate pathogens (Qu et al. 2013b). The photoactivity of nano-TiO2 can be improved by optimizing particle size and shape, lowering volume electron/hole (e−/ h+) recombination by noble metal doping and surface treatment for contaminant adsorption (Qu et al. 2013a, b).
TiO2 or TiO2-based materials A recently published review article captured the work about the application of TiO2 in arsenic removal in detail (Guan et al. 2012). In the study by Jézéquel and Chu (2005), they found that an increase of pH reduced As(V) adsorption on TiO2 nanoparticles due to the reduction of positively charged binding sites on the adsorbent’s surface. Also, it has been shown that at lower pH (pH 4), the maximum adsorption capacity according to Langmuir, was higher than at neutral pH. To improve the As(V) uptake at neutral pH, divalent cations (Mg and Ca) were added, and at a concentration of 7 mM, arsenate adsorption was increased from 2.1 to 6.5 and 7.7 mg As(V) g−1 TiO2, respectively. This effect suggests that the uptake capacity of TiO2 could be improved in removing As(V) from water. Nabi et al. (2009) synthesized pure and iron-doped TiO2 particles by the sol-gel method. The pure and iron-doped TiO2 nanoparticles were in
10.8
6
Hydrous titanium dioxide
Nanocrystalline TiO2
3.06 (UV light present)
<25 nm 937
0.56 (UV light absent)
<25 nm
TiO2-impregnated chitosan beads
875
409
Amorphous TiO2
TICB
4.8
98
Nanocrystalline TiO2
7.25
7.25
7.25
4.5
5.8
330
4.8
3.8
3-8
Hydrous titanium dioxide
280
5.9–6.9
Anatase NPs
UV absent UV present UV absent UV present
19
2.65
8.26
2.99
As(V)
As(V)
As(III)
2.89 3.10 2.54 3.83
3.54
2.10
As(III)
As(III)
2.05
19.0
As(V) As(V)
66.8
As(III)
38.4
>37.5
As(III) As(III)
>37.5
31.8
As(III) As(V)
33.4
96
83
16.98
As(V)
As(III)
As(V)
As(V)
As(V)
19.9
312
Ca and Mg ions
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
65
7
~6.9
Coexisting solutes
20.4
325
GPR TiO2 Pure TiO2 Iron-doped TiO2
~50
Specific surface area (m2 g−1)
pHpzc
108
30
Particle size (nm)
Properties
Comparative evaluation of various nano-adsorbent for arsenic removal
Degussa P25 TiO2
Nanoparticle
Table 1
pH<7, c(As)=10 mg L−1, adsorbent=30 % loading by mass, T=25 °C, synthetic groundwater
pH 6.6, c[As(III)]=0.01–10 mg L−1, adsorbent=0.625 g L−1, T=25 °C, model solution
pH 7.0, c[As(V)]=0.01–10 mg L−1, adsorbent=0.625 g L−1, T=25 °C, model solution
pH 7.7, c[As(V)]=0.01–10 mg L−1, adsorbent=0.625 g L−1, T=25 °C, model solution pH 9.2, c[As(III)]=0.01–10 mg L−1, adsorbent=0.625 g L−1, T=25 °C, model solution
pH 7, c[As(III)]=0.2–50 mg L−1, adsorbent=0.2 g L−1, model solution pH 7, c[As(III)]=0.2–50 mg L−1, adsorbent=0.2 g L−1, model solution pH 7, c[As(V)]=0.2–50 mg L−1, adsorbent=0.2 g L−1, model solution
pH 7±0.1, c[ As(V)]=45 mg L−1, adsorbent=1 g L−1, T=21–25 °C, model solution pH 7±0.1, c[As(III)]=45 mg L–1, adsorbent=1 g L–1, T=21–25 °C, model solution
pH 4, c[As(V)]=0.2–8.5 mg L−1, T=20–23 °C, model solution pH 4, c[As(III)]=0.2–8.5 mg L−1, T=20–23 °C, model solution
pH 7, c[As(III)]=0–170 mg L−1, adsorbent=0.5 g L−1, modelsolution pH 9, c[As(III)]=0–190 mg L−1, adsorbent=0.5 g L−1, model solution
pH 6.0, c[As(III)]=10 mg L−1, adsorbent=0, 015 g L−1, T=25 °C, model solution
pH 7, c[As(V)]=90 mg L−1, adsorbent=4 g L−1, model solution
pH 7, c[As(V)]=90 mg L−1, adsorbent=4 g L−1,model solution pH 7, c[As(V)]=90 mg L−1, adsorbent=4 g L−1, model solution
pH 4, c[As(V)]=5–30 mg L−1, adsorbent=1 g L−1, model solution pH 7, c[As(V)]=5–30 mg L−1, adsorbent=1 g L−1, model solution
Reaction conditions
Miller and Zimmerman (2011)
Miller and Zimmerman (2010)
Jegadeesan et al. (2010)
Jegadeesan et al. (2010)
Pena et al. (2005)
Pirilä et al. (2011)
Xu et al. (2010)
Özlem Kocabaş-Ataklı and Yürüm (2013)
Nabi et al. (2009)
Jézéquel and Chu (2005)
Reference
Environ Sci Pollut Res
~6 nm
3.5–8.7×10−3 12.1
59.08±7.8
Iron chitosan nanoparticles (CIN)
CS-NZVI-CMβ-CD
Commercial γ-Fe2O3
60
4
6
NANOFER25Sa
LNZVI
CNZVI (Nanofer 25)
20
5.5
7.3
35
As(V)
As
As(V)
34
85
107
135
47
As(V)
Ca-alginate NZVIa
95
5
α-Fe2O3 As(III)
1.94
89.58
α-Fe2O3a As(III)
25.0
16.7
13.51
As(V) As(V)
18.51
119±2.6
As(V) As(III)
94±1.5
45.5
As(V) As(III)
59.9
8.8 8.4 4.58 4.86 5.19 5.16
As(III)
As(V) As(III) As(III) As(V) As(III) As(V)
<10
<10
<5
<5
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
Sol-gel γ-Fe2O3
SO42−, HCO3−, NO3− PO43− (inhibited As adsorption)
UV present UV present
Coexisting solutes
50.0
6.5
7.25
pHpzc
Mechanochemical γ-Fe2O3
162
69
36.97
1.19
Mt-nZVI
176.4 (UV light absent) UV light present)
Specific surface area (m2 g−1)
1.83
Particle size (nm)
Properties
AlCB MICB TiO2/montmorillonite
Nanoparticle
Table 1 (continued)
pH 5, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 9, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 5, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution pH 7, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 7, c[As(V)]=53 mg L−1, adsorbent=1 g L−1, T=25 °C, groundwater spiked with arsenic solution pH 3.7–7.1, adsorbent=1 g L−1, model solution
pH 7, c[As(III)]=200 mg L−1, adsorbent=0.02 g L−1, model solution pH 7, c[As(V)]=200 mg L−1, adsorbent=0.02 g L−1, model solution
pH 2–10, c[As(III)]=0.5 mg L−1, adsorbent=1 g L−1, model solution pH 2–10, c[As(III)]=0.07 mg L−1, adsorbent=0.2 g L−1, model solution
pH 3, c[As(V)]=1–10 mg L−1, adsorbent=250 mg L−1, T=23 °C, model solution
pH 3, c[As(V)]=1–10 mg L−1, adsorbent=250 mg L−1, T=23 °C, model solution pH 3, c[As(V)]=1–10 mg L−1, adsorbent=250 mg L−1, T=23 °C, model solution
pH 6, c[As(III)]=1–20 mg L−1, adsorbent=0.1 g, T=25 °C, model solution pH 6, c[As(V)]=1–20 mg L−1, adsorbent=0.1 g, T=25 °C, model solution
pH 7, c[As(III)]=1–60 mg L−1, adsorbent=0.1 g, T=25 °C, model solution pH 7, c[As(V)]=1–60 mg L−1, adsorbent=0.1 g, T=25 °C, model solution
pH 7, c[As(III)]=2–345 mg L−1, adsorbent=1.29±0.05, T=22±1 °C, model solution pH 7, c[As(V)]=2–200 mg L−1, adsorbent=1.26±0.08, T=22±1 °C, model solution
pH 6.3–6.9, c(As)=1 mg L−1, adsorbent=2.325 mmol L−1 total metal, T=25 °C, model solution pH 7, c[As(III)]=5 mg L−1, T=25 °C, model solution pH 7, c[As(V)]=5 mg L−1, T=25 °C, model solution pH 7, c[As(III)]=5 mg L−1, T=25 °C, model solution pH 7, c[As(V)]=5 mg L−1, T=25 °C, model solution
Reaction conditions
Dong et al. (2012)
Klimkova et al. (2011)
Bezbaruah et al. (2013)
Tang et al. (2011a, b)
Prasad et al. (2011)
Tuutijärvi et al. (2009)
Tajuddin Sikder et al. (2014)
Gupta et al. (2012)
Bhowmick et al. (2014)
Li et al. (2012a)
Yamani et al. (2012)
Reference
Environ Sci Pollut Res
3.1
As(V)
10×103
34
1000
<50
20
cellulose@Fe2O3
Magnetite-γ-Fe2O3 mixture (EWE method)
Magnetite
γ-Fe2O3
Fe3O4a 60
39
40
12
23.26 32.11 2.9
As(III) As(V) As(III)
16.5
Fe3O4
7.4
As(V) As(tot)
6.6
8.8
As(V) As(III)
8.0
As(III)
20 4.9 5.68 4.78
47.76
3.84
As(V) As(III)
2.89
2.87
As(V) As(III)
2.41
As(III)
As(III) As(V) As(III) As(V)
Cl−, SO42−, PO43−
6.8
9.6
12.7
13
15
5
<10
<10
5.88
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
12.3
6.6
5.6
<4
Coexisting solutes
Fe2O3
113
Specific surface area (m2 g−1)
pHpzc
20–50
7
Particle size (nm)
Properties
Mag-Fe-Mna
Fe2O3/MnO2a
α-Fe2O3
CNZVIS (Nanofer 25S)
Nanoparticle
Table 1 (continued)
pH=8, c(As)=100 μg L−1, adsorbent=1 g L−1, 1 h, spiked groundwater pH=8, c(As)=100 μg L−1, adsorbent=0.5 g L−1, 1 h groundwater
pH 6, c[As(III)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution pH 6, c[As(V)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution
pH 6, c[As(III)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution pH 6, c[As(V)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution
pH 7, c[As(III)]=50 mg L−1, model solution pH 7, c[As(V)]=100 mg L−1, model solution pH 6, c[As(III)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution pH 6, c[As(V)]=1–7 mg L−1, adsorbent=1 g L−1, T=25±0.2 °C, model solution
pH 7, c[As(III)]=200 μg L−1, adsorbent=0.1 g L−1, model solution pH 6, c[As(III)]=0.3-100 mg L−1, adsorbent=10 mg, 24 h model solution pH 6, c[As(V)]=0.3-100 mg L−1, adsorbent=10 mg, 24 h, model solution
pH 4–7, c[As(V)]=1.5 mg L−1, adsorbent=50 mg L−1, T=25 °C, milling time 0.5 h, model solution
pH 4–7, c[As(III)]=1.5 mg L−1, adsorbent=50 mg L−1, T=25 °C, milling time 0.5 h, model solution
pH 4–7, c[As(III)]=1.5 mg L−1, adsorbent=50 mg L−1, T=25 °C, milling time 5 h, model solution pH 4–7, c[As(V)]=1.5 mg L−1, adsorbent=50 mg L−1, T=25 °C, milling time 5 h, model solution
pH 9, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 7, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 5, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 9, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
pH 7, c[As(V)]=2 mg L−1, adsorbent=150 mg L−1, model solution
Reaction conditions
Shipley et al. (2009)
Song et al. (2013)
Song et al. (2013)
Song et al. (2013)
Yu et al. (2013a)
Luther et al. (2012)
Shan and Tong (2013)
Andjelkovic et al. (2013)
Reference
Environ Sci Pollut Res
~5
8–13
10
20–40
Fe3O4
Fe3O4
Fe3O4@CTABa
Nanocrystalline Fe3O4
20–40
5
28
Fe3O4 and γ-Fe2O3
Manganese-Fe2O3 (MNHFO)a
Iron oxyhydroxidesa
67.02
As(III)
76.34
6.7 11.7 37.3
59.25
168.73
As(III) As(V) As(v)
As(V)
13
3.69
As(III) As(III)
3.71
3.7
As(III) As(V) As(V)
31.75
153.8
As(V) As(V)
188.69
45
As(III)
As(V)
As(III)
7–12
Phosphate (reduced the removal of As)
23.07
As(tot.) 3.65
As(V)
As(V)
0.4
46.06
As(III) As(tot)
2.8×10−3 2.4×10−3 16.56
32.18
As(III) As(V) As(V)
As(V)
pH=6.9, c(As)=1 mg L−1, adsorbent=1 g L−1, 24 h, T=25 °C, model solution pH 7, c(As)=100 μg L−1, adsorbent=50 mg L−1, model solution pH 7, c[As(V)]=0.12 mg L−1, adsorbent=60 mg L−1, T=27 °C, model solution pH 7, c[As(III)]=0.12 mg L−1, adsorbent =60 mg L−1, T=27 °C, model solution
Reaction conditions
38.8
<10
<10
<10
~5
pH 7, c[As(III)]=0.5–4 mg L−1, adsorbent=0.05 g L−1, model solution pH 7, c[As(V)]=100–1000 μg L−1, adsorbent=5– 25 mg, model solution pH 7, c[As(III)]=c[As(V)]=200–2000 μg L−1, adsorbent=5–25 mg, 20 °C, model solution pH 7, c[As(V)]=0–20 mg L−1, adsorbent=10 mg L−1, model solution pH, c[As(V)]=100 mg L−1, adsorbent=1 g L−1, model solution pH 6, c[As(III)]=10–150 mg L−1, adsorbent=0.16 g, T=10 °C pH 6, c[As(III)]=10–150 mg L−1,adsorbent=0.16 g, T=30 °C
pH 6, c[As(V)]=10 mg L−1, adsorbent=1 g L−1, T=30 °C, model solution pH=2, c(As)=2 mg L−1, adsorbent=0.4 g L−1, model solution pH 2, c[As(V)]=0.5–4 mg L−1, adsorbent=0.4 g L−1, model solution pH 2, c[As(III)]=0.5–4 mg L−1, adsorbent=0.4 g L−1 model solution
pH 7, c[As(V)]=100 mg L−1, adsorbent=2.15 g L−1, model solution pH 7, c[As(III)]=2 mg L−1, adsorbent=1 g L−1, model solution pH 7, c[As(V)]=2 mg L−1, adsorbent=1 g L−1, model solution
pH 6, c[As(V)]=100 μg L−1, adsorbent=0.1 g L−1, model solution c(As)=5 mg L−1, adsorbent=8 g L−1, model solution
As(tot)=15.30 pH 8.2, c[As(V)]=1.57 mg L−1, c[As(III)]=0.28 As(V)=12.56 mg L−1, adsorbent=8 g L−1, T=25±1 °C, natural water pH 2.5, c[As(V)]=0.01–1 mg L−1, adsorbent=8 g L−1, T=25–65 °C, model solution
82 80
50
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
γ-Fe2O3
135
3.1
4.3
6.4
7.4
Coexisting solutes
As(V)
20
187
120
186.28
49
100
0.1–11.9
178.48
218.6
Specific surface area (m2 g−1)
pHpzc
α-FeOOH
δ-FeOOH
Fe/MnOOH
2
20
Fe3O4
a
20
P(4-VP)-HCl nanoparticle
Fe3O4
γ-Fe2O3
300 nm
Particle size (nm)
Properties
Hematite-coated Fe3O4
Fe3O4–BNNT(e)
Nanoparticle
Table 1 (continued)
Lin et al. (2012)
Ghosh et al. (2012)
Faria et al. (2014)
Tresintsi et al. (2012)
Gupta et al. (2010)
Chowdhury et al. (2011b)
Chowdhury et al. (2011a)
Sahiner et al. (2011)
Lunge et al. (2014)
Kilianová et al. (2013)
Bujňáková et al. (2012)
Jin et al. (2012)
Akin et al. (2012)
Feng et al. (2012a)
Simeonidis et al. (2011)
Chen et al. (2011)
Reference
Environ Sci Pollut Res
52.11
40
100-150
15-25
CuO
Malachite
CaO2
NHIAO-250 °C (hydrous Fe(III) Al(III) mixed oxide
86.51
CuO
85
12-18
CuOa
29.61
282
2-50
CeO2-ZrO2
116
86.85
116.96
153.9
Specific surface area (m2 g−1)
Fe-Cu binary oxide
9.9
Hydrous CeO2 (SCO40)
6.6±0.9
70–90
Ceria/manganese (NCMO)
Ceria NPs
25–35
Particle size (nm)
Properties
γ-Fe2O3-TiO2
Nanoparticle
Table 1 (continued)
5.9
7.5
7.9
6.5
pHpzc
95.37 105.25
26.52
As(V) As(V)
• CO32−, SiO32−, HPO42− As(III) • SO42−, NO3−, Cl−, Ca2+, Mg2+ (no impact on As removal) As(V)
As(III)
As(III)
As(V)
As(tot)
58.3±3.15
57.1
1.09
22.6
As(V) As(tot)
26.9
122.3 82.7
145.35
116.840.7
7.0
17.08
As(III)
As(III) As(V)
As(III) As(V)
As(V
As(III)
As(tot)
88.44
As(V)
18.65
74.83
24
12.5
<3 (ground water)
18.3
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
As(III)
Coexisting solutes
pH~6, c(As)=100 μg L−1, adsorbent=8 g L−1, 20 h, column test, spiked groundwater pH 8, c(As)=0.5−1 mg L−1, adsorbent=1 g L−1, model solution pH 5, c[As(V)]=100 mg L−1, adsorbent=5 g L−1, T=30 °C, model solution pH 7.5, c[As(III)]=0.2 mg L−1, adsorbent=40 mg L−1, 0.5 h, model solution pH 7, c[As(III)]=5.5 mg L−1, adsorbent=2 g L−1, T=30 °C, groundwater
pH 7, c[As(III)]=10 mg L−1, adsorbent=200 mg L−1, T=25±0.1 °C, model solution pH 7, c[As(V)]=10 mg L−1, adsorbent=200 mg L−1, T=25±0.1 °C, model solution pH 8, c[As(III)]=0.1–100 mg L−1, adsorbent=2 g L−1, model solution pH 8, c[As(V)]=0.1–100 mg L−1, adsorbent=2 g L−1, model solution
pH~6.9, c[As(III)]=0.5–6 mg L−1, adsorbent=0.2 g L−1, model solution pH~6.9, c[As(V)]=0.5–6 mg L−1, adsorbent=0.2 g L−1, model solution
pH 7, c[As(V)]=5 mg L−1, adsorbent=0.5 g L−1, model solution pH 3−11, c[As(V)]=0.4–10 μg L−1, adsorbent=5 g L−1, model solution pH 7, c[As(III)]=~100 μg L−1, adsorbent=0.015 g L−1, natural water pH 6.8, c[As(V)]=~100 μg L−1, adsorbent=0.015 g L−1, natural water
pH=7.0±0.1, c[As(III)]=50 mg L−1, adsorbent=0.5 g L−1, model solution
pH 3, c[As(V)]=10–200 mg L−1, adsorbent =0.16 g, T=50 °C model solutions
pH 3, c[As(V)]=10–200 mg L−1adsorbent=0.16 g, T=30 °C
pH 3, c[As(V)]=10–200 mg L−1,adsorbent=0.16 g, T=10 °C
pH 6, c[As(III)]=10–150 mg L−1,adsorbent=0.16 g, T=50 °C
Reaction conditions
Basu and Ghosh (2011)
Olyaie et al. (2011)
Saikia et al. (2011)
Goswami et al. (2012)
Reddy et al. (2013)
Martinson and Reddy (2009)
Zhang et al. (2013a)
Xu et al. (2013)
Sun et al. (2012)
Feng et al. (2012b)
Gupta et al. (2011)
Yu et al. (2013b)
Reference
Environ Sci Pollut Res
781
Fe-doped AC (PBFe-BM-Act)
18.0
10
γ- Fe2O3-coated zeolite (MNCZ)
3–6
50
γ-Al2O3
Aluminum cryogel
9.4±2
2 2
α-Fe2O3–polymer monolith Fe3O4–polymer monolith
Polymer nanocomposite (Fe3O4)
13
Mn0.5Cu0.5Fe1.2Al0.8O4
CeO2-CNT
26
80–250
156
50 60
189
126
896 806 1058 998 1101 635 26
F400-Fe ACZ-Fe ACP-Fe F400-M CAZ-M CAP-M CFe CarFe α-Fe2O3 on ACO-9
~6
CMC-stabilized Fe-Mn NPs
348±46
903±4
Bituminous Zr-GAC
100
438.2
330
0.8·103
Al-doped phenolic bead
Superparamagnetic Mg0.27Fe2.50O4 3.7
104
Specific surface area (m2 g−1)
10-20
Particle size (nm)
Properties
iron(III)–cerium(IV) mixed oxide (NICMO)
Nanoparticle
Table 1 (continued)
8.9 2.3 2.7 6.05 4.04 3.57 10
7,13
pHpzc
NO3−, SO42−, PO43−
Ca2+ Mg2+
Cl−, F−, PO43−, SO42−
9.5 % Zr content
Coexisting solutes
As(V)
As(tot)
As(III)
As(III)
As(V)
As(V)
As(V)
As(V)
As(V)
As(V)
As(V)
As(III) As(V) As(III) As(V)
5.68
As(V)
20.3±0.8
2.83
3.1
2.7
81.9 78.8 0.053
19.39
3.25 1.45 1.65 0.847 0.431 0.181 – 2.11 27.78
338 272 182 372
3.0
14.83
83.2
As(V) As(III)
127.4
As(III)
20
2.1
As(V) As(V)
2.42
As(III)
25
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
pH=8.6, c[As(III)]=5–100 mg L−1, adsorbent=1.7 g L−1, T=26 °C, model solution C(As)=100 μg L−1, adsorbent=0.1 g L−1, groundwater
pH 7, c[As(V)]=20 μg L−1, adsorbent=100 g L−1, model solution pH 7, c[As(V)]=5 mg L−1, adsorbent=0.0225 g L−1, T=25 °C, model solution pH=2.5, c[As(V)]=20 mg L−1, adsorbent=1 g L−1, T=22±2 °C, model solution pH=7, c[As(V)]=20 mg L−1, adsorbent=0.025 g L−1, natural water pH=6, c[As(V)]=20-200 μg L−1, adsorbent=0.05 g, T=40 °C, model solution pH=3–12, c[As(III)]=4 mg L−1, adsorbent=0.5 g, model solution pH=3–12, c[As(III)]=4 mg L−1, adsorbent=0.5 g, model solution
pH 7, c[As(V)]=50 μg L−1, adsorbent=0.75 g L−1, T=25 °C, well water
pH 7, c[As(V)]=1 μg L−1, T=25 °C, model solution
pH 7.6±0.2, c(As)=120 μg L−1, adsorbent=0.03–0.65 g L−1, T=25±0.1 °C, model groundwater pH 5.5, c(As)=5–140 mg L−1, adsorbent=0.27 g L−1, model solution pH 3, c(As)=5–140 mg L−1, adsorbent=0.27 g L−1, model solution
pH 7, c[As(III)]=20 mg L−1, adsorbent=0.1 g L−1, T=30 °C, wastewater pH 6.5, c[As(V)]=20 mg L−1, adsorbent=0.1 g L−1, T=30 °C, wastewater
pH 7, c[As(V)]=1–50 μg L−1, adsorbent=2 g L−1, T=30 °C, model solution pH 7, c[As(III)]=0.097 mg L−1, adsorbent=0.01 g L−1, T=25 °C, natural water pH 7, c[As(V)]=0.101 mg L−1, adsorbent=0.01 g L−1, T=25 °C, natural water
pH 7, c[As(III)]=4.8 mg L−1, adsorbent=2 g L−1, T=30 °C, model solution pH 7, c[As(V)]=4.5 mg L−1, adsorbent=0.05 g L−1, T=30 °C, model solution
Reaction conditions
Önnby et al. (2012)
Patra et al. (2012)
Vunain et al. (2013)
Savina et al. (2011)
Malana et al. (2011)
Peng et al. (2005)
Attia et al. (2014)
Yürüm et al. (2014)
Gutierrez-Muñiz et al. (2013)
Vitela-Rodriguez and Rangel-Mendez (2013)
Nieto-Delgado and Rangel-Mendez (2012)
An and Zhao (2012)
Sandoval et al. (2011)
Sharma et al. (2010)
Tang et al. (2013)
Kumar et al. (2011)
Basu and Ghosh (2013)
Reference
Environ Sci Pollut Res
420.9
RGO-ZrO(OH)2 (1:100)
284 27.7 47.7
30−50
14.9 μm 15.3 μm
Monolithic Fe2O3/graphene
Perlite/γ-Fe2O3 Perlite/α-MnO2
a
7.1 4.8
7.13
pHpzc
Residual concentration meets the regulation limit of 10 μg L−1
Biochar-AlOOH
100.65
nZVI-RGO
2.27
111.5
19±9
Silver containing yeast cells Fe3O4-RGO-MnO2 (3:8)
98
7
ZrO2a
Specific surface area (m2 g−1)
327.1
<38 μm
Particle size (nm)
Properties
Al2O3 encapsulated polymer bead ZrO2
MIP-cryogel
Nanoparticle
Table 1 (continued)
Cl−, SO42−, PO43−, S2−
Coexisting solutes
As(V)
As(V) 17.41
4.64 7.09
35.83 29.04
84.89
As(V) As(III) As(V) As(V)
14.04 12.22 95.15
As(III) As(V) As(III)
0.975
9.0
As(V) As(V)
9.2
32.4
As(V) As(III)
83
6.56
As(III)
As(V)
7.9±0.7
67
10
Arsenic Adsorption Residual species capacity concentration Γmax (μg L−1) (mg g−1)
c[As(V)]=50 mg L−1, adsorbent=0.1 g, T=22±0.5 °C, model solution
pH=7, c[As(V)]=20 mg L , adsorbent=0.05 g, T=25±0.5 °C, model solution
−1
pH=7, c[As(V)+As(III)]=1–15 μg L−1, adsorbent=10 mg, T=25±0.5 °C, model solution c[As(V)]=85 μg L−1, model solution
pH=3–11, c[As(V)]=2 mg L−1, adsorbent=2 g L−1, model solution pH=7, c[As(V)]=0.01–10 mg L−1, adsorbent=5 mg, T=25.5±0.2 °C, model solution pH=7, c[As(III)]=2–80 mg L−1, adsorbent=10 mg, T=25.5±0.2 °C, model solution pH=7, c[As(III)]=2–80 mg L−1, adsorbent=10 mg, T=25.5±0.2 °C, model solution
pH=7.1, c[As(III)]=0.212 mg L−1, adsorbent=0.005–0.06 g L−1, model solution pH=7.1, c[As(V)]=0.355 mg L−1, adsorbent=0.01–0.1 g L−1, model solution
pH=7, c[As(V)]=5±0.013 mg L−1, adsorbent=40 g L−1, spiked wastewater pH=7.2, c[As(V)]=25–80 mg L−1, adsorbent=2 g, T=30 °C, model solution pH=7, c[As(III)]=70 mg L−1, adsorbent=0.1 g L−1, T=25 °C, model solution and natural water pH=7, c[As(V)]=70 mg L−1, adsorbent=0.1 g L−1, T=25 °C, model solution and natural water
Reaction conditions
Zhang and Gao (2013)
Nguyen Thanh et al. (2011)
Li et al. (2014)
Wang et al. (2014)
Luo et al. (2013)
Luo et al. (2012)
Selvakumar et al. (2011)
Cui et al. (2013)
Cui et al. (2012)
Saha and Sarkar (2012)
Reference
Environ Sci Pollut Res
Environ Sci Pollut Res
100 % anatase crystalline phase with crystal sizes of 108 and 65 nm, which were revealed by X-ray diffraction (XRD) analysis. The Freundlich model described the adsorption isotherms as well as Langmuir, and the results showed that the Freundlich coefficient (KF) ranged from 2.32 to 8.50, while the Freundlich exponent (n) ranged from 2.04 to 4.76. In all three types of TiO2 nanoparticles, the sorption capability from general purpose reagent (minimum) to iron-doped TiO2 (maximum) was increased by increasing the KF values. Also, an increase in Langmuir model coefficient (KL) was evident. Finally, it has been shown that the adsorption efficiency of TiO2 nanoparticles can be improved by iron doping resulting in a higher affinity for arsenic. Özlem Kocabaş-Ataklı and Yürüm (2013) investigated anatase nanoparticles for lead, copper, and arsenic uptake from contaminated water. The adsorbed arsenic concentrations were consistent with the changes of pH, while the adsorbed amounts of lead and copper increased with increasing pH. The maximum adsorption uptakes were 31.25 mg g−1 for lead, 23.74 mg g−1 for copper, and 16.98 mg g−1 for arsenic, respectively. In the adsorption process, surface oxygen with functional groups and hydroxyl groups was included. Hence, the whole Pb(II), Cu(II), and As(III) sorption studies on the nanoparticles showed that polluted water could be treated with these synthesized nanoparticles. Hydrous TiO2 Xu et al. (2010) synthesized hydrous titanium dioxide (TiO2 · xH2O) nanoparticles by a low-cost one-step hydrolysis process with aqueous TiCl4 solution. These (TiO2 ·xH2O) nanoparticles ranged from 3 to 8 nm and formed aggregates with a highly porous structure, resulting in a large surface area and easy removal capability from the aqueous environment after the treatment. The adsorption capacity on As(III) of these (TiO2 ·xH2O) nanoparticles reached over 83 mg g−1 at near neutral pH and over 96 mg g−1 at pH 9.0. Adsorption experiments conducted with an As(III)-contaminated natural lake water sample confirmed the effectiveness of TiO2 ·xH2O nanoparticles in removing As(III) from natural water of Lake Yangzonghai. The high adsorption capacity of the TiO2 ·xH2O nanoparticles was related to the high surface area, large pore volume, and the presence of high affinity surface hydroxyl groups. With only a relatively low material loading concentration (0.08 g L−1), they successfully removed most of the As(III) and the residual concentrations met the USEPA standard for arsenic in drinking water. Pirilä et al. (2011) studied an industrial intermediate product for the removal of aqueous arsenic. The tested material functioned well in removing both of these arsenic forms. The apparent values for Langmuir monolayer sorption capacities were 31.8, 32.1, and 25.8 mg g−1 for As(III) and 33.4, 22.0, and 26.8 mg g −1 for As(V) at pH 4, 5, and 6,
respectively. The studied TiO2 performed the best in acidic conditions but also reasonably well in other pH conditions. Nanocrystalline TiO2 Pena et al. (2005) evaluated the effectiveness of nanocrystalline titanium dioxide (crystalline size was ~6 nm) in removing arsenate and arsenite. Batch adsorption and oxidation experiments were conducted with TiO2 suspensions prepared in a NaCl solution and in challenge water containing competing anions (phosphate, silicate, and carbonate). The removal of As(V) and As(III) reached equilibrium within 4 h. TiO2 was effective for As(V) removal at pH<8 and showed a maximum removal capacity for As(III) around pH of 7.5. The adsorption capacity of the TiO2 for As(V) and As(III) was much higher than fumed TiO2 (Degussa P25) and granular ferric oxide. More than 0.5 mmol g−1 of As(V) and As(III) was adsorbed by the TiO2 at an equilibrium arsenic concentration of 0.6 mM. Jegadeesan et al. (2010) prepared amorphous (labeled as STiO2) and crystalline (labeled as H-TiO2) TiO2 nanoparticles by calcining the amorphous TiO2 nanoparticles at different temperatures. The effect of TiO2 characteristics and preparation techniques was studied. The capacities of the TiO2 particles prepared in the study (S, A, B, C, and D) for arsenic sorption were similar but were significantly lower than the commercially available H-TiO2 (prepared via sol-gel synthesis of titanium sulfate salts), which can be linked with the particle characteristics and preparation procedures. Amorphous TiO2 could enhance the arsenic adsorption due to the large surface area and modified chemical and physical features. This study revealed that the adsorption capacities of STiO2 and H-TiO2 for As(III) were∼3.5 and∼2.0 times of those for As(V) under neutral conditions, respectively. The oxidation of As(III) on the surface increases the effectiveness of As(III) removal. TiO2-impregnated chitosan bead The research by Miller and Zimmerman (2010) showed that the TiO2-impregnated chitosan bead (TICB) system performs similarly to the mass equivalent of neat TiO 2 nanopowder. Without exposure to UV light, TICB removes 2198 μg As(III) g−1 and 2050 μg As(V) g−1. With exposure to UV light, TICB achieves photooxidation of As(III) to As(V), reaching sorption capacities of 6400 μg As(III) g−1 and 4925 μg As(V) g−1. Most of TICB’s arsenic sorption capacity can be attributed to TiO2, as the TiO2 content of TICB can account for >97 % removal of the arsenic added as As(III) and >67 % removal of the arsenic added as As(V). Additionally, Miller et al. (2011) investigated the optimization of TICB for arsenic removal to improve the adsorption capacity and kinetics. The adsorption capacity of the
Environ Sci Pollut Res
adsorbent was pH and TiO2 loading dependent and was enhanced with UV light. Results revealed that arsenate was significantly removed below pH 7.25 and arsenite below pH 9.2. In addition, the removal efficiency increased with exposure to UV light and reduction in bead size. Groundwater ions, such as Ca, Mg, and Si, were not competitors with arsenite for adsorption sites on TICB, while phosphate was. To improve the original TICB, new improved sorbent has been developed by Yamani et al. (2012) which incorporated two nanopowder metal oxides, nanocrystalline Al2O3 and nanocrystalline TiO2, into a chitosan matrix. Such adsorbent (MICB) exploited the high capacity of Al2O3 for arsenate and the photocatalytic activity of TiO2 to oxidize arsenite to arsenate, resulting in arsenic removal capacity higher than that of either metal oxide alone. Results of this research showed that only a small amount of TiO2 is required to oxidize arsenite to arsenate, with removal likely by Al2O3. The effect of agitation speed on arsenate removal in the dark was also investigated, and since there was no appreciable difference between the system agitated at 150 rpm (about 75 % arsenic removed) and the unagitated system (about 40 % arsenic was removed), the authors suggested that film diffusion was not limited.
TiO2/montmorillonite (TiO2/MMT) Li et al. (2012a) conducted experiments in which they changed the inactive sodium ions of montmorillonite with TiO2 which enhanced the arsenic uptake. The arsenic adsorption experiments demonstrated that TiO2/MMT can effectively remove arsenic from aqueous solutions under a wide range of experimental conditions, including pH, adsorption time, and UV light. The equilibrium concentrations of As(III) and As(V) were less than 10 μg L−1, especially with UV irradiation. The adsorption kinetics fit the pseudo-second order model well and results indicated that up to 90 % of As(III) and up to 87 % of As(V) were absorbed within 10 min with UV irradiation. Compared to nanocrystalline titanium dioxide, TiO2/MMT has many advantages in arsenic adsorption like faster adsorption rate, low equilibrium concentration of As(III) (0 μg L−1) and As(V) (4 μg L−1) with UV irradiation, and better cost efficiency.
Iron-based nanoparticles One of the most important nanomaterials studied for water purification is zerovalent iron (ZVI). Among the most used nano-adsorbents, ZVI is the most utilized, primarily because it covers the broadest range of environmental contaminants: halogenated organics, pesticides, arsenic, nitrate, and heavy metals (Li et al. 2006) (Fig. 2).
Fig. 2 Schematic model of magnetic nanoparticles (nZVI, Fe3O4, and γFe2O3). Zerovalent iron in the core mainly provides the reducing power for reactions with contaminants. The oxide shell provides sites for sorption. Adsorption also occurred on the iron oxide (Fe3O4 and γFe2O3) surfaces, while Fe3O4 possesses reducing power (Tang and Lo 2013)
Zerovalent iron nanoparticles Studies that have investigated the application of zerovalent iron reported its high adsorption capacities for most of the toxic metals. nZVI is a suitable option for the fast removal of contaminants from aqueous solution and is extensively used for arsenic removal (Li et al. 2006; Morgada et al. 2009). ZVI nanoparticles can rapidly remove and/or reduce these inorganic ions. Also, it has relatively higher capacity than conventional sorptive media and granular iron particles (Li et al. 2006). The oxidation of nano-zerovalent iron by water and oxygen produces ferrous iron to give magnetite, depending upon redox conditions and pH which eventually facilitates the magnetic separation (Kanel et al. 2005). The basis for the reaction is the corrosion of zerovalent iron in the environment (Nowack 2008): 2 Fe0 þ 4Hþ þ O2 →2Fe2þ þ 2H2 O Fe0 þ 2H2 O→ Fe2þ þ H2 þ 2OH−
Increasing evidence suggests that nZVI is effective for the removal of arsenic from contaminated water, but the immobilization mechanism is unclear. It is generally accepted that the main mechanism of arsenic removal by ZVI involves adsorption, reduction, surface precipitation, and coprecipitation with various iron corrosion products such as ferrous/ferric (hydr)oxides (Mak et al. 2009). However, the operating conditions may have an important role in controlling the overall effectiveness of arsenic removal. Therefore, in order to gain a better understanding of the overall removal mechanism, it is necessary to define the effect of
Environ Sci Pollut Res
key parameters, such as pH, dissolved oxygen, hardness, and humic acid (HA) on arsenic removal (Fu et al. 2014). Ramos et al. (2009) studied the mechanism of As immobilization on nanoparticulate ZVI using high-resolution X-ray photoelectronic spectroscopy (HR-XPS) and confirmed clear evidence of As(0) formation together with As(III) and As(V) on the nanoparticle surface after reaction with As(III) or As(V) species in solutions. The obtained results proved that both reductive and oxidative mechanisms take place during nZVI application. The dual redox function exhibited by nZVI is enabled by the core-shell structure of nZVI, which contains a highly reducing metal core and a thin layer of amorphous iron (oxy)hydroxide, promoting As(III) coordination and oxidation. The distinct layers where As(V) and As(0) reside imply As(III) oxidation and reduction are enabled by different components of the nanoparticles. These results revealed the underlying mechanisms of arsenic reactions with nZVI suggesting nZVI as a potential versatile agent for arsenic remediation (Ramos et al. 2009; Yan et al. 2010). However, Litter et al. (2010) reported that the mayor disadvantage of nZVI is its complicated synthesis. Mak et al. (2009) investigated the arsenic(V) removal using zerovalent iron from humic acid (HA)-deficient and HA-rich groundwater. The authors reported that arsenic was removed from groundwater by adsorption and coprecipitation on iron corrosion products. Investigating the effect of calcium ions and alkalinity (HCO3−), they also reported that in the presence of HCO3− and Ca2+, the arsenic removal efficiency increased with increasing concentrations of either Ca2+ or HCO3−. In HA-free groundwater samples, CaCO3 was acted as a nucleation seed for the growth of iron (hydr)oxides. These large iron (hydr)oxide particles (>0.45 μm) were responsible for the rapid removal of arsenic, while without the aid of CaCO3, only colloidal iron (hydr)oxide (<0.45 μm) can exist. The authors emphasized that in the presence of HA, the formation of CaCO3 was delayed leading to the subsequent delay in the formation of large iron (hydr)oxide particles which inhibited arsenic removal in the earlier stages, while in the absence of hardness or the presence of HA, the concentration of total dissolved iron may be elevated causing esthetic concerns. Klimkova et al. (2011) treated acid mine water from in situ chemical leaching of uranium in laboratory-scale experiments by zerovalent iron nanoparticles (Nanofer 25S). Due to an increase in pH and a decrease in oxidation-reduction potential, a decrease in concentrations of monitored pollutants (As, Be, Cd, Cr, Cu, Ni, U, V, and Zn) was observed. The proposed mechanisms of the pollutant removal are (a) cation precipitation, (b) precipitation caused by pH increment, and (c) coprecipitation with iron oxyhydroxides. Arsenic is more soluble in As(V) form than in As(III), but As(III) anions are adsorbed and coprecipitated with hydrous ferrous/ferric oxides, formed during oxidation of nZVI in water. According to this mechanism, concentrations of As decreased below the
detection limits of ICP-OES (0.01 mg L−1) after application for all diluted samples. Dong et al. (2012) investigated the desorption efficiency of As by fate of As(V)-treated nZVI (As-NZVI) in different conditions. As the predominant mechanism of As(V) removal by nZVI is adsorption onto the nZVI corrosion products, the adsorption isotherm for the As(V) uptake on the three types of nZVIs [i.e., LNZVI, CNZVI (Nanofer 25), and CNZVIS (Nanofer 25S)] was examined, and a Langmuir adsorption isotherm was able to describe As(V) adsorption by each of the three types of nZVIs. For LNZVI, values of qmax were 135, 107, and 85 mg g−1, respectively, at pH 5, 7, and 9; for CNZVI, values of qmax were 34, 15, and 13 mg g−1, respectively, at pH 5, 7, and 9; and for CNZVIS, the equation gave values of qmax 12.7, 9.6, and 6.8 mg g−1, respectively, at pH 5, 7, and 9. Adsorption of As(V) by each of the three types of nZVIs decreased with increasing pH over the pH range from 5 to 9. The ionization of As(V) and the adsorbents was in correlation with pH. The nZVI is characterized by high agglomeration tendency, high mobility, lack of stability, and low reducing specificity in water and, thus, must be used with surface stabilizers such as chitosan, alginate, activated carbon, and other porous structures (He and Zhao 2005). For this reason, Gupta et al. (2012) prepared novel inorganicorganic iron chitosan nanoparticles (CIN) for arsenic removal. The addition of chitosan enhanced the stability of Fe(0) nanoparticles. The results showed that, with an initial nanoparticle dose of 0.5 g L−1, concentrations of As(III) and As(V) can be reduced from 2 mg L −1 to <5 μg L−1 in less than 180 min, and the adsorbent was found to be applicable in wide range of pH. Langmuir monolayer adsorption capacity was found to be 94±1.5 and 119±2.6 mg g−1 at pH 7 for As(III) and As(V), respectively. Major anions including sulfate, phosphate, and silicate did not interfere in the adsorption behavior of both arsenite and arsenate. Thus, the adsorbent was recycled five times and applied to the removal of total inorganic arsenic from contaminated groundwater samples which were in accordance with WHO drinking water standards. Tajuddin Sikder et al. (2014) tested nZVI-impregnated chitosan-carboxymethyl β-cyclodextrin (CS-nZVI-CMβCD) complex for As(III) and As(V) removal. The carboxymethyl β-cyclodextrin gives the composite more active sites to interact with the target ions. Removal of arsenic(III) and arsenic(V) was studied through batch adsorption at pH 6.0 under equilibrium and dynamic conditions. This CS-nZVI-CMβ-CD bead showed that a combined effect of highly dispersed nZVI particles and highly functional CS-CMβ-CD surface gives a fast kinetics to remove both As(III) and As(V) supported by early equilibrium with high adsorption and respective speciation. The adsorption capacities was found to be 18.51 and
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13.51 mg g−1 for As(III) and As(V), respectively. Additionally, the adsorbent could be separated magnetically and thus reused successfully for the removal of total inorganic arsenic from water. The influence of six selected species (phosphate (PO43−), bicarbonate (HCO3−), sulfate (SO42−), calcium (Ca2+), chloride (Cl−), and humic acid (HA) ions) on arsenic removal by nZVI, both single and multiple species systems, was investigated by Tanboonchuy et al. (2012). As a result, in both systems, the important species which played a significant role in removing arsenic were HA, PO43−, and Ca2+, with the first two species imposing an inhibiting effect and the last one an enhancing effect. In particular, SO42− played an inhibiting role in a single species system but a promoting role in multiple species system. The presence of HCO3− in both systems inhibited As(V) removal only slightly, but the inhibition became significant in As(III) removal. Hence, Tanboonchuy et al. (2012) suggested that the arsenic removal by the nanoiron process can be improved through pretreatment of PO43− and HA. In addition, for the groundwater with high hardness, the nanoiron process can be an advantageous option because of the enhancing characteristics of Ca2+. Tandon et al. (2013) developed a one-step method that is based on the use of plant parts (Tata tea leaves) for the synthesis of zerovalent iron nanoparticles supported on montmorillonite K10 at room temperature. It has been shown that depending on the loading of nZVI on MMT K10, the supported nanoparticles were found to be able to remove As(III) from water to the extent of 99 % within 30 min at both low and high p H v a l u e s ( 2 . 7 5 a n d 11 . 1 ) . E x p e r i m e n t s w i t h montmorillonite-supported nanoscale zerovalent iron (MtnZVI) on arsenic removal have been carried out by Bhowmick et al. (2014), and it has been shown that the dispersion of nZVI onto montmorillonite was found to be increased with decreasing tendency to agglomerate into larger particles. Batch experiments revealed that adsorption kinetics followed pseudosecond order rate equation with high affinity toward both As(III) and As(V) over a wide pH range (4–8) which was decreased at pH>9. The maximum adsorption capacity calculated from the Langmuir adsorption isotherm was found to be 59.9 and 45.5 mg g−1 for As(III) and As(V), respectively, at pH 7.0. Although the presence of competing anions like SO42 − , HCO3−, and NO3− did not show a pronounced effect, PO43− had an inhibitory action on the adsorption. The research by Bezbaruah et al. (2014) evaluated Caalginate-entrapped nZVI as an advanced treatment technique for aqueous arsenic removal. In batch studies using solution with initial As(V) concentrations ranging from 1 to 10 mg L−1, between 85 and 100 % arsenic removal was achieved within 2 h. The entrapped nZVI removed 100 μg L−1 As(V) to below detection limit within 2 h. Using the groundwater with initial As(V) concentration of 53 μg L−1, the authors reported arsenic removal below 10 μg L−1 within
1 h. The presence of Na+, Ca2+, Cl−, and HCO3− did not affect removal by entrapped nZVI.
Iron oxide nanoparticles The most interesting feature of magnetic nanoparticles is the easy separation from the dissipated medium by magnetic force (Sharma et al. 2009; Mahmood et al. 2013). Iron oxides play a major role in many areas of chemistry, physics, and material science. Besides suitable magnetic properties, low toxicity, and price, iron oxide nanoparticles exhibit high surface to volume ratios, which when associated to their ability for surface chemical modification can show enhanced capacity for metal uptake in water treatment procedures (Mahmood et al. 2013). γ-Fe2O3 nanoparticles Iron oxide as a nano-adsorbent is able to remove arsenic five to ten times more effectively than their micron-size counterparts. Tuutijärvi et al. (2009) reported that the adsorption capacity of As(V) was as high as 50 mg g−1 when γ-Fe2O3 nanoparticles were prepared. For nanoscale γFe2O3 with a surface area of 200 m2 g−1 at pH 3, the maximum absorption was 50 mg g−1, while at pH∼9, it was lower by 3 %. The removal efficiency was observed as dependent upon surface area, surface charge (pH), and applied background magnetic field (Ambashta and Sillanpää 2010). Prasad et al. (2011) utilized nanoparticles of iron oxide, obtained as waste from the cold rolling mill (CRM) of an integrated steel company, to remove arsenite (As3+) from arsenic-contaminated water. The major component of the CRM fine powder was the rhombohedral phase, α-Fe2O3. Kinetics study revealed that adsorption of arsenic by CRM fines within the first 60 min of contact was 60–80 % of the amount removed after the equilibrium was achieved in 120 min. The adsorption efficiency increases with the decrease of initial pH. The powder, with a mean particle size around 90 nm, has been found to have an excellent arsenic adsorption capacity, which can be explained by the Langmuir isotherm equation. The monolayer adsorption capacity of the CRM fines has been found to be 1.94×103 μg g−1. In addition to removing arsenic, the system was capable of reducing the hazardous contaminants and bacteria substantially. Tang et al. (2011a) achieved about 90 % As(III) removal and more than 80 % of As(V) using ultrafine α-Fe2O3 nanoparticles which were synthesized by the solvent thermal process without the addition of surfactants or templates. Another research by Tang et al. (2011b) showed that with the increase of material loading (α-Fe2O3), the rate of the As(III) removal increases and the final As(III) concentration in the treated water samples decreases. At lower initial As(III) concentration, it has been found that ~73 and ~98.3 % of As(III) in the water sample could be removed with just 0.01 and 0.04 g L−1 α-Fe2O3 material loadings, respectively.
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Lin et al. (2012) reported the results of arsenite and arsenate removal using synthesized magnetic γ-Fe2O3 nanoparticles. The nanoparticles were synthesized by a coprecipitation method at room temperature. The authors reported results in terms of a Langmuir model at different temperatures. The adsorption capacities for As(III) were 59.25, 67.02, and 74.83 mg g−1 at 10, 30, and 50 °C, respectively, and for As(V), the adsorption capacities were 88.44, 95.37, and 105.25 mg g−1 at the same temperatures, respectively. The adsorption capacity was pH independent (from pH 3 to 11) and the presence of Cl−, SO42−, and NO3− had no effect on the adsorption capacity. Only PO43− decreased the adsorption capacity of arsenic due to its outer electronic structure similar to arsenic. In addition, results showed that after 6 cycles, nanoparticles had over 40 % of initial adsorption capacity. Luther et al. (2012) synthesized nanophase Fe2O3 and Fe3O4 for As(III) and As(V) removal. For this purpose, under a 1-h contact time, batch pH experiments were performed to determine the optimum pH binding using 300 μg L−1 of either As(III) or As(V) and 10 mg of either Fe2O3 and Fe3O4. It was evident that there has been no influence of the pH from 6 to 9 on adsorption, while a decrease in adsorption efficiency was observed at pH 10. In order to determine the adsorption capacity of both As(III) and As(V), batch isotherm studies were conducted. The adsorption was found to follow the Langmuir isotherm and the capacities of 1250 mg kg−1 (Fe2O3) and 8196 mg kg−1 (Fe3O4) for As(III) as well as 20,000 mg kg−1 (Fe2O3) and 5680 mg kg−1 (Fe3O4) for As(III), at 1 and 24 h of contact time, respectively. The As(V) capacities were determined to be 4600 mg kg−1 (Fe2O3), 6711 mg kg−1 (Fe3O4), 4904 mg kg−1 (Fe2O3), and 4780 mg kg−1 (Fe3O4) at contact times of 1 and 24 h respectively. Yu et al. (2013a) applied a universal, simple method in the preparation of the cellulose-based magnetic iron oxide nanoparticles through a green pathway. The Fe2O3 nanoparticles were uniformly dispersed in the cellulose matrix due to the strong interaction between cellulose and Fe2O3 nanoparticles. The cellulose@Fe2O3 nanoparticle composites exhibit a sensitive magnetic response and superparamagnetic behavior with an external magnetic field. The arsenic could be accumulated on the surface of the cellulose@Fe2O3 composites. The results showed that the magnetic nanoparticle composites displayed excellent adsorption efficiency of arsenic compared with other magnetic materials reported, and the Langmuir adsorption capacities of the composites for the removal of arsenite and arsenate were 23.16 and 32.11 mg g−1, respectively. Fe3O4 nanoparticles (magnetite nanoparticles) There has been much interest in magnetite (Fe3O4) due to its utility in adsorbing high concentrations of arsenic from contaminated water. The magnetic properties of the material allow for simple dispersion and removal from an aqueous system (Van Dorn et al. 2011). The research by Vaclavikova et al. (2008)
proved that synthesized magnetite is an efficient sorbent for As removal from water solutions and maximum capacities observed were around 30 mg As g−1 of solid magnetite. Iron oxide nanoparticles with dimercaptosuccinic acid (DMSA) to create dispersible sorbent that can be magnetically collected were functionalized by Yantasee et al. (2007). The affinity of DMSA-Fe3O4 for As was more modest than for other metals and similar to that on unmodified Fe3O4, which is indicative that the DMSA ligand shell had very little impact upon As capture. This supports the irreversible adsorption of As onto the core material. Nevertheless, the massive improvement in Kd (distribution coefficient, mL g−1) values clearly shows the excellent utilization of the DMSA ligand shell. In this research, the Kd value for arsenic was 5400 mL g−1, which is relatively low compared to silver (3,600,000 mL g−1) or lead (2,300,000 mL g−1) when filtered groundwater was tested. The effect of Zn2+ on both the kinetic and equilibrium behavior of arsenic adsorption to magnetite nanoparticles was investigated by Yang et al. (2010). Results showed that Zn2+ in the solution improved the adsorption of As(III) and As(V) at neutral to alkaline pH. Using initial concentrations of 100 mg L−1 and initial pH of 8, very low concentrations of Zn2+ (less than 3 mg L−1) increased arsenate and arsenite removal by magnetite nanoparticles from 66 to over 99 % and from 80 to 95 %, respectively. Other cations, such as Ca2+ and Ag+, have not enhanced arsenic adsorption. Shipley et al. (2009) conducted arsenate and arsenite adsorption to 0.1 and 0.5 g L−1 magnetite nanoparticles. Results showed that during 1 h, adsorption and magnetite dose of 0.1 g L −1 adsorbed 48.5 μg L −1 of As(V) and 51.2 μg L−1 of As(III) from the solution with an initial concentration of 100 μg L−1 (expressed as As). Magnetite nanoparticles at 0.5 g L−1 adsorbed 92.6 μg L−1 arsenate and 93.9 μg L−1 arsenite during 1 h. With an initial arsenic concentration of 100 μg L−1, arsenate and arsenite had similar affinity for the magnetite nanoparticles. The MCL for arsenic was achieved using 0.5 g L−1 magnetite nanoparticles for both arsenic species. Additionally, the authors stated that the adsorption follows the pseudo-first order and a semiempirical adsorption kinetics model was developed for arsenic removal by magnetite nanoparticles. Shipley et al. (2010) examined iron oxide nanoparticles on arsenate and arsenite removal through column studies (FeNP/soil column). The results showed that arsenic is adsorbing to the magnetite nanoparticles but not to the soil. The total arsenic loading on the magnetite nanoparticles with initial concentrations of 100 and 500 μg L−1 was 2.9 and 4.0 μg m−2. Chen (2004) used multiwalled boron nitride nanotubes (BNNTs) functionalized with Fe3O4 nanoparticles for arsenic removal from water. Batch adsorption experiments were conducted at neutral pH (6.9) and room temperature (25 °C), and using the developed nanocomposites showed effective As(V) removal. The Langmuir, Freundlich, and Dubinin-
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Radushkevich adsorption isotherms were measured for a range of As(V) initial concentrations from 1 to 40 mg L−1 under the same conditions. Experimental data fitted well the all isotherms, indicating that the mechanism for As(V) adsorption was a combination of chemical complexation and physical electrostatic attraction with a slight preference for chemisorption. The products of conventional and surfactant-assisted ballmilling of magnetite powder as potential arsenic adsorbents were tested by Simeonidis et al. (2011). Large hematite-coated Fe3O4 particles obtained without the addition of surfactant were found to be much more efficient to reduce arsenic levels below the international regulation limit (10 μg L−1) having an adsorption capacity of 2.1 μg mg−1. On the contrary, the 30nm Fe3O4 nanoparticles coated with oleic acid could only decrease arsenic concentration below 45 μg L−1. Akin et al. (2012) synthesized Fe3O4 nanoparticles by using bauxite residue (waste red mud) from Seydişehir aluminum factory (Seydişehir, Konya, Turkey) and to study the potential use of the synthesized Fe3O4 nanoparticles for the removal of As(V) from synthetic and natural groundwater samples. The used water contained 1570 μg L−1 of As(V) and 280 μg L−1 of As(III). Under optimum conditions, the results showed that the removal of As(V) from groundwater sample was 99.2 %. The residual As(V) concentration of the sample was 12.56 μg L−1. Also, the authors stated that an additional adsorption step can be employed when single-stage adsorption is not enough to reduce the residual arsenic concentration below 10 μg L−1 (Akin et al. 2012). The research conducted by Feng et al. (2012a) reported that supermagnetic ascorbic acid-coated Fe3O4 nanoparticles with a high specific surface area effectively removed arsenic ions from water. The use of the ascorbic acid not only improved the dispersibility of Fe3O4 nanoparticles in aqueous suspensions but also effectively inhibited the leaching of Fe into the solution. The adsorption data obeyed the Langmuir equation with maximum adsorption capacities of 16.56 mg g −1 for arsenic(V) and 46.06 mg g−1 for arsenic(III). This application of Fe3O4 nanoparticles for heavy metal removal has a great potential in wastewater engineering. Jin et al. (2012) reported that modification of cetyltrimethylammonium bromide (CTAB) greatly enhanced As(V) adsorption capacity from 7.59 to 23.07 mg g−1 which is over 95 % removal of As(V) (100 μg L−1) using 0.1 g L−1 Fe3O4@CTAB within 2 min at pH 6 and more than 90 % at a wide pH range from 3 to 9. Arsenate adsorption agreed well with pseudo-second order kinetic model and two-site Langmuir isotherm model with the arsenate adsorption capacity of 23.07 mg g−1, which was twice greater than the results obtained using pure Fe3O4. Additionally, Fe3O4@CTAB could be regenerated and more than 85 % As(V) was removed even in fifth reuse cycle.
The research by Patel et al. (2012) tested and compared arsenite removal by nanocrystalline barium hexaferrite (BaFe12O19, BHF) and commercial magnetite nanoparticles (Fe3O4) with granulation between 50 and 100 nm. The study revealed that BHF showed better (75 %) arsenic(III) removal than magnetite of the similar sizes. The authors reported that the maximum arsenite adsorption capacities for BHF are 2.27 and 0.7 mg g−1 for magnetite. This behavior suggests that hexaferrites of nanodimensional size gave better arsenic removal efficiency than commercial Fe3O4 nanoparticles. Bujňáková et al. (2013) tested nanocrystalline magnetite sorbent which showed maximum adsorption capacity 3.65 mg g−1 and more than 90 % of arsenic removal from the model water solution with a concentration of 5 mg L−1. The positive influence of the mechanical activation on magnetite mineral rests in the reduction of crystal size (from micro- to nanodimensions) and consequent increase of the specific surface area, SA, from 0.1 to 11.9 m2 g−1, which appears to have an essential role in sorption kinetics. Desorption of arsenic was also studied to determine the possibility of the magnetite sorbent regeneration (over 70 % of arsenic was removed in the first two cycles using KOH and NaOH). Kilianová et al. (2013) conducted a simple and cheap synthesis of ultrafine iron(III) oxide nanoparticles with a narrow size distribution and their exploitation in the field of arsenate removal from an aqueous environment. The authors reported that the adsorption capacity was enhanced by a mesoporous nature of nanoparticle arrangement in the system due to strong magnetic interactions between nanoparticles. A complete arsenate removal was achieved at Fe/As ratio equal to 20:1 and at pH in the range from 5 to 7.6. Under these conditions, the arsenates were completely removed within several minutes of treatment. Monárez-Cordero et al. (2014) employed magnetite nanoparticles, which were synthesized by aerosol-assisted chemical vapor deposition (AACDV) technique, for arsenic removal. The results showed a very high efficiency for removal of both As(III) and As(V) ions. Before 1 min of contact, arsenic ions were completely removed from water achieving almost 100 % of efficiency. Thus, arsenic removal was carried out very fast, which means that the affinity iron for arsenic is very strong. Besides this affinity, the rapid adsorption of the metal ions on the MNPs is also produced by the high specific surface area of the adsorbents. A recent research by Lunge et al. (2014) showed how magnetic iron oxide nanoparticles (crystal structure of Fe3O4–magnetite), synthesized using MION-Tea waste template, were very efficient in As(III) and As(V) removal, because the tea waste improves the crystalline nature of Fe3O4 nanoparticles. The adsorption data obeyed the Langmuir equation with high adsorption capacity of 188.69 mg g−1 for As(III) and 153.8 mg g−1 for As(V). However, the presence of other anions like chloride, nitrate, sulfate, and
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phosphate had a negative effect on As(III) adsorption. Additionally, an important fact is that MION-Tea was of very low cost and can be reused up to five adsorption cycles and regenerated using NaOH. Sahiner et al. (2011) prepared nanogels from Fe 3O 4 (370 nm dimension) based on 4-vinylpyridine (p-(4VP)) using redox and microemulsion techniques. The p(4-VP)-based materials were quaternized with HCl/alkyhalides having different chain lengths to tune the charges (macro and nanogels) and size of nanogels. By developing positive charge on the p(4VP) materials, they behaved as ion exchangers and used in the removal of As(V) from aqueous environments. Nanoparticles quaternized with HCl (p(4-VP)-HCl) (1 g) removed over 95 % of As(V) from a stock solution (10 mg L−1, 1000 mL) in 15 min, whereas bulk hydrogels removed >82 % of the As(V) from an equivalent solution within 12 h. Mixed magnetite-γ-Fe2O3 nanoparticles Because of the large surface area of magnetite nanoparticles, they have a good adsorption affinity for heavy metals. Shipley et al. (2011) reported that magnetite nanoparticles reduced the aqueous arsenic concentration to below 10 μg L−1 within 10 min when the initial arsenic concentration was 100 μg L−1. Less than 1 g L−1 of magnetite nanoparticles was needed due to its large surface area. The results suggest that arsenic adsorption to the nanoparticles was not significantly affected by pH, ionic strength, and temperature which are usual for natural waters. The results showed that pH, ionic strength, and temperature had minimal effect on arsenic adsorption. Song et al. (2013) tested arsenic removal using iron oxide nanoparticle synthesized by electrical wire explosion (EWE). The XRD characterization showed that synthesized iron-oxide nanoparticles were composed of 55.8 wt% magnetite and 44.2 wt% γ-Fe2O3. Arsenite and arsenate adsorption tests were performed at room temperature and pH 6, in a period of 24 h with an adsorbent dose of 1 g L−1, while As concentrations were ranging from 1 to 7 mg L−1. The authors reported that maximum sorption capacities of iron oxide nanoparticles prepared by EWE were 2.9 mg g−1 for arsenite and 3.1 mg g−1 for arsenate. Chowdhury and Yanful (2011a) used magnetite nanoparticles for arsenic removal from water. The results revealed that the maximum arsenic adsorption (3.70 mg g−1 for both As(III) and As(V)) occurred at initial arsenic concentrations of 2 mg L−1 and pH 2. Weak arsenic-iron oxide complexes at magnetite surface were formed. The dose of the adsorbent was constant (0.4 g L−1) and it has been shown that arsenic removal decreased with increasing phosphate concentration. Magnetite nanoparticles removed <50 % of arsenic from water containing >6 mg L−1 phosphate. Furthermore, the authors used commercially grade nanosize Bmagnetite,^ later identified in laboratory characterization to be mixed magnetite-γFe2O3 nanoparticles, in the uptake of arsenic and chromium
from water. The results showed 96–99 % arsenic and chromium uptake under controlled pH conditions. The maximum arsenic adsorption occurred at pH 2 with values of 3.69 mg g−1 for arsenic(III) and 3.71 mg g−1 for arsenic(V) when the initial concentration was kept at 1.5 mg L−1 for both arsenic species, while chromium(VI) concentration was 2.4 mg g−1 at pH 2 with an initial chromium(VI) concentration of 1 mg L−1. Thus, magnetite-γ-Fe2O3 nanoparticles can adsorb arsenic and chromium in an acidic pH range. Additionally, the results showed the limitation of arsenic and chromium uptake by the nanosize magnetite-γ-Fe2O3 mixture in the presence of a competing anion such as phosphate (Chowdhury and Yanful 2010). Other research conducted by Chowdhury et al. (2011b) showed that magnetite-γ-Fe2O3 nanoparticles can adsorb As(III) and As(V) better in an acidic pH range. For 2 mg L−1 of As(V) and As(III) concentrations, equilibrium was achieved in 3 h at pH 6.5 and it has been suggested that 2 g L−1 of magnetite nanoparticles adsorbent can be used to remove at least 95 % of As(III) and As(V) from water. In general, As(V) and As(III) removal increased with increasing the masses of adsorbent at fixed PO43− concentration of 10 mg L−1. The authors also reported that the arsenic adsorption capacity of the magnetite nanoparticles at room temperature, calculated from the Langmuir isotherm, was 62.66 μmol g−1. Liang et al. (2013) reported that starch and carboxymethyl cellulose were great stabilizers during the preparation of magnetite nanoparticles and thus adsorbed arsenic more effectively than other iron oxide particles. Changing the type and concentration of the stabilizer, particle stability, degree of aggregation, and size may be controlled. In addition, As(V) uptake was enhanced at lower pH, while As(III) sorption was observed in a wide pH range. Hydrous iron oxide nanoparticles Gupta et al. (2010) prepared manganese-associated hydrous iron(III) oxide (MNHFO) by heat treatment. By increasing the incineration temperature, crystalline phases increased, while As(III) removal decreased. Optimization of pH indicated that MNHFO-1 could remove As(III) efficiently at pH between 3.0 and 7.0. Kinetic and equilibrium data of reactions under the experimental conditions described the pseudo-second order and the Langmuir isotherm equations very well, respectively. The sorption reaction with MNHFO-1 was endothermic and spontaneous with increasing entropy. Tresintsi et al. (2012) used iron oxyhydroxides as arsenic sorbents. Its production was focused mainly on their ability to decrease residual arsenic concentration below the regulation limit of 10 μg L−1 preferably than studying the maximum capacity. The results showed higher adsorption capacity for As(III) (108.7 μg mg−1) in comparison to that for As(V) (48.8 μg mg−1) at equilibrium concentrations in the range of 0.1−10 mg L−1. This optimized adsorbent presents the highest reported adsorption capacity while keeping the residual
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arsenic below 10 μg L−1. In addition, results showed that these adsorbents could be treated as nonhazardous waste according to the toxicity characteristic leaching procedure (TCLP) test. δ-FeOOH nanoparticles were prepared by Faria et al. (2014). Zeta potential revealed that the point of zero charge of δFeOOH is 8.4, which favored the As(V) adsorption on the δ-FeOOH surface even at neutral pH. The As(V) adsorption capacity of δ-FeOOH was estimated to be 37.3 mg g−1 at pH 7. This high adsorption capacity was assigned to the small particle size and the high specific surface area of δ-FeOOH (Faria et al. 2014). Other metal-based nanoparticles Goethite nanoparticles Ghosh et al. (2012) reported goethite nanoparticulate as good adsorbent for the As(V) removal. Results showed that maximum adsorption occurred at pH 3.0. The adsorption data fitted well to the Langmuir isotherm equation supporting that adsorption was monolayer (maximum adsorption capacity obtained experimentally was 72.4 mg g−1 and matched closely with the monolayer adsorption capacity of 76.3 mg g−1) calculated from the Langmuir isotherm. Also, it was shown that an adsorbent dose of 6 g L−1 was sufficient for removing more than 99 % As(V) from a solution containing 50 mg L−1 As(V). It was also evident that As-loaded adsorbent could be regenerated with an alkaline solution of pH 13.0. Ceria nanoparticles Gupta et al. (2011) synthesized nanostructured ceria incorporated manganese oxide (NCMO) by redox conversion coprecipitation-calcination and sol-gel methods. The NCMO-1b sample, prepared by the calcination of metal hydroxide at 573 K for 3.0 h, was a nanocrystalline (70–90 nm) and hydrated material having a high BET surface area (116.96 m2 g−1). The arsenic(V) sorption by the samples at pH 7.0 (±0.2) and 30 °C showed that the NCMO-1b is a most efficient material. Optimum pH range for the arsenic(V) sorption was 3.0–7.0 at 303 (±1.0) K. Kinetics and equilibrium data obtained had described the pseudo-second order kinetics (10.012 mg g−1 for arsenic concentration of 10.8 mg L−1 and 13.738 mg L−1 for arsenic concentration of 20.0 mg L−1) and the Freundlich isotherm models (9.020 mg g −1 ) well, respectively. Feng et al. (2012b) tested ceria nanoparticles for arsenic adsorption. The results showed that the adsorption efficiency was pH dependent, but independent of ionic strength, indicating that the electrostatic effect on the adsorption of these elements was relatively not important compared to surface complexation reactions. The Langmuir adsorption capacities of this nanoparticle were 17.08, 18.02, and 18.15 mg g−1 at
temperatures of 283, 303, and 323 K, respectively, while the Freundlich adsorption capacities were 1.32, 1.40, and 2.32 mg g−1 at 283, 303, and 323 K, respectively. From these results, it has been concluded that the adsorption of arsenic on ceria nanoparticles in both models increased with the rise of temperature. Hydrous cerium oxide (HCO) nanoparticles synthesized by Li et al. (2012b) demonstrated exceptional adsorption properties in terms of adsorption capacity and kinetics on both As(III) and As(V). At neutral pH, the arsenic adsorption capacity of HCO reached over 170 mg g−1 for As(III) and 107 mg g−1 for As(V). Even at very low equilibrium arsenic concentrations, the amount of As(III) and As(V) adsorbed by HCO nanoparticles was still over 13 and 40 mg g−1 when 10 and 50 μg L−1 initial arsenic solution was used. Sun et al. (2012) developed a composite arsenic adsorbent (SCO) by integrating CeO2 nanoparticles onto silica monoliths. Because CeO2 is the active adsorption component in SCO adsorbent, results showed that the arsenic removal speed increases and the final arsenic concentration in the treated water samples decreases for both As(III) and As(V) with the increase of CeO2 loading. The arsenic removal rate was fast, especially for As(III), and the removal gradually reached the equilibrium with the increase of treatment time. Over 85 % As(III) in the solution (initial concentration of 106 μg L−1) was adsorbed in just 30 min when the SCO40 loading was just 0.015 g L−1, and the equilibrium As(III) concentration was 2.65 μg L−1 after the treatment, which was far below the arsenic MCL suggested by WHO in drinking water. To improve ceria nanoparticles (NPs) for arsenic removal, Xu et al. (2013) demonstrated that the hierarchically porous CeO2ZrO2 nanospheres could be prepared via the Kirkendall effect and could be used as an effective adsorbent for arsenic removal. The CeO2-ZrO2 nanospheres exhibited an adsorption capacity of about 27.1 and 9.2 mg g−1 for As(V) and As(III), respectively, at an equilibrium arsenic concentration of 0.01 mg L−1 under neutral conditions. Pore accessibility and abundant surface hydroxyl group densities were the major factors responsible for their excellent adsorption capacity. In addition, the CeO2-ZrO2 nanospheres were able to remove over 97 % arsenic from real groundwater with an initial arsenic concentration of 0.376 mg L−1. Cupric oxide nanoparticles Martinson and Reddy (2009) synthesized CuO nanoparticles for As(III) and As(V) removal. At initial As(III) and As(V) concentrations of 0.1 to 100 mg L−1, CuO nanoparticles showed the best removal efficiency at pH ranging from 6 to 10. The maximum adsorption capacities were 26.9 mg g−1 for As(III) and 22.6 mg g−1 for As(V). The adsorption of As(III) was slightly inhibited by sulfate and silicate in water, while no
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impact on As(V) adsorption was evident. However, elevated concentrations of phosphate (>0.2 mM) had a negative effect on arsenic removal. Saikia et al. (2011) reported of high adsorption capacities for chromate and arsenate ions on malachite nanoparticles. However, the adsorption efficiency decreased with the increase of solution pH. Batch studies revealed that initial pH, temperature, malachite nanoparticle dose, and initial concentration of chromate and arsenate were important parameters for the adsorption process. The adsorption process was well fitted by the Langmuir isotherm with maximum monolayer coverage of 82.2 and 57.1 mg g−1 for chromate and arsenate, respectively. Adsorption experiments with CuO nanoparticles were carried out with different process parameters such as contact time, adsorbent dose, pH, temperature, and stirring speed. Results showed that the adsorption process followed pseudosecond order kinetic and endothermic behavior. The sorption of arsenic onto CuO nanoparticles was found to be highly pH dependent. Under the following conditions of 200 μg L−1 initial arsenic concentrations, 1 g L−1 adsorbent dose, and a contact time of 300 min, 100 % of arsenic was adsorbed. The percentage adsorption was decreased with the increase of initial arsenic concentration. The presence of phosphate and sulfate ions reduced arsenic adsorption percentage by more than 20 percentage and less than 10 percentage, respectively, on the surface of CuO nanoparticles (Goswami et al. 2012). Batch adsorption kinetic experiments were conducted in order to determine the time course of uptake of arsenic by CuO nanoparticles by Reddy et al. (2013). They developed a reactor with CuO nanoparticles and conducted continuous flow-through experiments to filter arsenic from groundwater samples. The samples were spiked with 100 μg L−1 of arsenic passed through the reactor. The results revealed that the arsenic adsorption process by CuO nanoparticles followed the pseudo-second order rate. Adsorptions of arsenic at both initial concentrations (4 and 0.2 mg L−1) were very rapid. Within 30 min, most of the arsenic was adsorbed by CuO nanoparticles. At the lower arsenic concentration, CuO nanoparticle showed the highest capacity to adsorb arsenic. Moreover, arsenic adsorption per unit of nanoparticle was decreased with increasing concentrations of nanoparticle in solution. Therefore, it can be concluded that the removal of arsenic by CuO nanoparticles should be efficient at a lower concentration than at a higher one. In addition, regenerated CuO nanoparticles showed also good adsorption efficiency. Arsenic mass balance data from regeneration studies suggested that regeneration of adsorbent was 99 % efficient. Calcium peroxide nanoparticles Olyaie et al. (2012) synthesized calcium peroxide nanoparticles and demonstrated their capability to effectively remove
arsenic from contaminated aqueous solution. In the adsorption processes, the efficiency of CaO2 nanoparticles decreased by increasing pH and arsenic concentration in solution. Removal efficiency had a direct relation to contact time and dosage of CaO2 nanoparticles. Up to 88 % arsenic removal efficiency was obtained by nanoparticles’ dosage of 40 mg L−1 at time equal to 30 min and pH 7.5. The maximum removal of arsenic(III) was found to be 91 % at pH 6.5, and hence, this removal technique is effective to bring the arsenic concentration under the advised limit of 10 μg L−1 of WHO. Aluminum oxide nanoparticles Patra et al. (2012) concluded that self-assembled mesoporous γ-Al2O3 spherical nanoparticles can be synthesized hydrothermally by using the supramolecular assembly of sodium salicylate as a template. Salicylate anions ligated with the positively charged Al(III) centers through covalent interaction during the synthesis process. Further, the H-bonding interactions between the phenolic –OH groups could help to form the supramolecular structure of salicylate moieties during synthesis, which on calcination generate mesopores with dimensions of 3–6 nm depending upon the synthesis temperatures. The results showed that about 70 % of As(V) was removed after 4 h, and generally, the removal efficiency increased with time of adsorption kinetics but decreased with the number of cycles. Regarding pH, results showed that about 75 % of arsenic was removed at pH 6, while the removal efficiency decreased at higher pH. Zirconium oxide nanoparticles Cui et al. (2012) synthesized amorphous zirconium oxide adsorbent (am-ZrO2) nanoparticles for effective arsenic removal from aqueous environment. Am-ZrO2 nanoparticles demonstrated an effective removal performance on both As(III) and As(V) in either lab-prepared or natural water samples. The adsorption capacities of these am-ZrO2 nanoparticles on As(III) and As(V) at pH 7 were 83.2 and 32.5 mg g−1, respectively. The adsorption mechanism of arsenic species onto amZrO2 nanoparticles was determined to follow the inner-sphere complex mechanism. Further, Cui et al. (2013) synthesized nanostructured ZrO2 spheres from amorphous ZrO2 nanoparticles with the assistance of a food-safe additive, agar powder, which provided a simple, low-cost, and safe process for the synthesis. The ZrO2 spheres demonstrated a good adsorption capacity on both As(III) and As(V) at near neutral pH environment; thus, preoxidation and/or pH adjustment of the arsenic-contaminated water is not necessary. In addition, ZrO2 spheres are nontoxic, highly stable, and resistant to acid and alkali; have a high arsenic adsorption capacity; and could be easily adapted for various arsenic removal apparatus.
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Silver nanoparticles Selvakumar et al. (2011) developed adsorbent nanoparticles for arsenate removal using silver reducing property of the novel yeast strain Saccharomyces cerevisiae BU-MBT-CY1 isolated from coconut cell sap. The yeast cells after biological silver reduction were harvested and subjected to carbonization at 400 °C for 1 h. Increased As(V) adsorption capacity of 0.975 mg g−1 was achieved using carbonized silver containing yeast cells (CSY) compared to 0.236 mg g−1 using carbonized control yeast cells (CCY). A desorption study showed that As(V) adsorbed onto the CSY could be desorbed up to 49.2 %. Since the CSY contained silver nanoparticles on its surface, the water disinfection effect was also achieved.
Mixed oxide nanoparticles Iron-manganese Tresintsi et al. (2013) reported on highly efficient As(III) and As(V) adsorbing single-phase Fe/Mn oxyhydroxide. In natural-like water, Mn(IV)-feroxyhyte removed 11.7 μg As(V)/mg and 6.7 μg As(III)/mg at pH 7. In the study by Andjelkovic et al. (2014), the mixture of Fe2O3/MnO2 was prepared. Among the prepared sorbents, the mixture of Fe2O3/MnO2 =3:1 gave the best results. Adsorption capacities, derived from Langmuir isotherms, were 2.89 and 3.84 mg g−1 for arsenite and arsenate, respectively. Removal was efficient in the pH range of 4–7 (up to 89 % of As(V) was removed, while 80 % of As(III) was removed at pH 4 and by increasing pH, removal efficiencies decreased). Shan and Tong (2013) modified magnetic nanoparticles with amorphous Fe and Mn oxides (Mag-Fe-Mn) for arsenic removal from water. Results showed that at neutral pH, 200 μg L−1 of As(III) could be easily decreased below 10 μg L−1 within 20 min. As(III) could be effectively removed by Mag-Fe-Mn particles at initial pH range from 4 to 8, and the residual As was completely oxidized to less toxic arsenate [As(V)]. The co-occurring redox reactions between Mn oxide and As(III) was confirmed by XPS analysis. Iron-titanium nanoparticles Yu et al. (2013b) prepared Fe-Ti binary oxide nanomaterial with magnetic property for As(III) removal. The prepared γFe2O3-TiO2 nanoparticles are characterized by the photocatalytic ability of TiO2 (anatase) for oxidation of As(III) to As(V) and the adsorption performance of γ-Fe2O3 for the removal of As(V). The maximal removal capability for As(III) was 33.03 mg g−1 at solution pH 7.0 and initial As(III) concentration 50 mg L−1. Results showed that phosphate was the greatest competitor with arsenic for adsorptive sites on the surface of the nanomaterial. Furthermore, ionic strength and the presence of SO42−, NO3−, Cl−, Ca2+, and Mg2+ had no significant effect on arsenic removal.
Fe(III)-Al(III) mixed oxide nanoparticles Basu and Ghosh (2011) tested hydrous iron(III)-aluminum(III) mixed oxide (NHIAO) for As(III) removal at temperature 30 °C and optimized pH 7.0 (±0.2). Results showed that the incinerated NHIAO at 250 °C had the highest As(III) removal efficiency. The presence of SO42−, PO43−, and HCO3− reduced the arsenic removal efficiency of NHIAO to about 12–16 % which was visible when the Langmuir capacity (58.30±3.15 mg g−1) in the absence of other ion at background was compared with the results obtained in the presence of either ions tested. Used in column, NHIAO reduced well arsenic and other spiked ions in groundwater improving the quality of treated water. Similarly, Kumar et al. (2011) incorporated Al and Fe into polymeric beads during an intermediate step of the synthesis by suspension polymerization. The synthesized Al- and Fedoped nanosized porous adsorbents possessed significant loadings of fluoride (100 mg g − 1 ) and arsenic(V) (40 mg g−1) ions. The methodology adopted in this study to prepare bimetal-doped carbon-based porous adsorbents is a step toward developing multifunctional adsorbents for water remediation applications. Iron(III)-cerium(IV) mixed oxide (NICMO) Basu and Ghosh (2013) developed an efficient nanostructured iron(III)cerium(IV) mixed oxide (NICMO) by an eco-friendly green synthetic route. Results showed that the pseudo-second order kinetic model described very well the arsenic sorption kinetics when some groundwater ions are present. Thus, chloride, sulfate, bicarbonate, and phosphate ions had an impact on As(III) sorption capacity of the bimetal mixed oxide. Values of the experimental arsenic sorption amounts (qt) were found to be more close to the modeled (q′t) values of pseudo-second order kinetics. While As(III) is the dominant species in groundwater, NICMO could be applied for the treatment of arseniccontaminated water because of its influence on groundwater occurring ions. The authors emphasized that the stronger adverse influence of major occurring ions on the arsenite and arsenate adsorption onto NICMO indicated the possible extensive applicability of NICMO for arsenite-rich groundwaters. Iron(III)-copper(II) binary oxide Developing composite sorbents containing two or more metal oxides have gained considerable attention, since the composite not only inherits the advantages of the parent oxides but shows obviously a synergistic effect. For this purpose, Zhang et al. (2013a) synthesized a nanostructured Fe-Cu binary oxide via a facile coprecipitation method. Excellent arsenic removal efficiency was achieved using Fe-Cu binary oxide with a Cu/Fe molar ratio of 1:2, and the maximal adsorption capacities for As(V) and As(III) were 82.7 and 122.3 mg g−1 at pH 7.0, respectively. Coexisting ions, such as phosphates, decreased the arsenic removal
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efficiency, while sulfates and carbonate ions had no impact on arsenic removal. Magnesium ferrite Superparamagnetic ultrafine magnesium ferrite (Mg0.27Fe2.50O4) nanoadsorbent synthesized by Tang et al. (2013) demonstrated high arsenic adsorption performance on both As(III) and As(V). The adsorption capacities on both As(III) and As(V) were no less than 127.4 and 83.2 mg g−1, respectively. At an equilibrium arsenic concentration of 0.01 mg g −1 , about 101 mg g −1 As(III) and 11.8 mg g−1 As(V) were adsorbed. The arsenic adsorption performance was enhanced by surface hydroxyl groups, and also it has been shown that the nanoadsorbent followed the inner-sphere complex mechanism. It is important to note that such nanoadsorbent could be separated from water by a magnet and after regeneration still having acceptable arsenic removal efficiency. Modified and activated carbons and zeolites Muñiz et al. (2009) reported that iron-doped activated carbons (ACs) are much more efficient for As uptake, and therefore, a number of samples were synthesized by impregnation of raw and oxidized ACs with HCl aqueous solutions of either FeCl3 or FeCl2 at various concentrations and various pH values. Fe was homogenously distributed in the form of nanoparticles. It has been shown that iron(II) chloride is better for obtaining high iron contents in the resultant ACs (up to 8.34 wt%), leading to high As uptake, close to 0.036 mg As g−1 C. In these conditions, 100 % of the As initially present in the natural well water was removed, as soon as the Fe content of the adsorbent was higher than 2 wt%. Fierro et al. (2009) reported that ferric chloride hydrolysis was a good method for increasing the iron content of ACs. The AC obtained after 6 h of ferric chloride hydrolysis removed 94 % of the initial arsenic concentration, whereas the commercial AC used as precursor allowed the removal of only 14 %. Cooper et al. (2010) investigated the impact of the type of granular activated carbon (GAC) media used to synthesize iron (hydr)oxide nanoparticle-impregnated granular activated carbon (Fe-GAC) on its properties and its ability to remove arsenate and organic trichloroethylene (TCE) from water. Two Fe-GAC media were synthesized via a permanganate/ferrous ion synthesis method using bituminous and lignite-based GAC. Data obtained from an array of characterization techniques (pore size distribution, surface charge, etc.) in correlation with batch equilibrium tests and continuous flow modeling suggested that GAC type and pore size distribution control the iron (nanoparticle) contents, Fe-GAC synthesis mechanisms, and contaminant removal performances. The results show that arsenic removal capability was increased, while TCE removal was decreased as a result of impregnation of Fe nanoparticles. This trade-off is related to several factors,
of which changes in surface properties and pore size distributions appeared to be the most dominant. Sharma et al. (2010) prepared iron-doped activated micro/ nanocarbon particles as efficient adsorbents for arsenic removal. Iron (Fe) was incorporated in an intermediate step during polymerization. In an alternate route to preparing the adsorbents, the synthesized polymeric beads were first milled, carbonized, and activated. The prepared absorbent particles were applied in the removal of arsenic (III and V) present at low concentration levels (<20 mg L−1) in water. The method in which milling was performed first produced a superior adsorbent. For both arsenic ions, the equilibrium loading (3– 15 mg g−1) in the adsorbate was found to be comparable to the adsorbates reported in the literature. The optimum performance of the prepared adsorbents was observed at pH range between 6.5 and 7.5. Sandoval et al. (2011) investigated the effects of in situ ZrO2 nanoparticle formation on the properties of GAC and their impacts on arsenic and organic co-contaminant removal. Bituminous and lignite-based zirconium dioxide-impregnated GAC (Zr-GAC) media were fabricated by hydrolysis of zirconium salt followed by annealing of the product at 400 °C in an inert environment. The arsenic removal performance of both media was compared using 5 mM NaHCO3 buffered ultrapure water and model groundwater containing competing ions, both with an initial arsenic concentration of 120 μg L−1. The increased surface area and better accessibility to the ZrO2 nanoparticles could be attributed to the better arsenic removal performance of the bituminous Zr-GAC under equilibrium and continuous flow conditions. Zirconium metal oxidebased hybrid media may offer a viable alternative to other metal (hydr)oxide hybrid-based media for simultaneous removal of multiple inorganic (e.g., arsenic) and organic contaminants. Nieto-Delgado and Rangel-Mendez (2012) proved that thermal hydrolysis is an excellent method to anchor iron hydro(oxide) nanoparticles onto granular activated carbons. The effects of hydrolysis temperature (60–120 °C), hydrolysis time (4–16 h), and FeCl3 concentration (0.4–3 mol Fe L−1) were studied. Higher adsorption capacities showed materials with smaller iron hydro(oxide) particles. The arsenic adsorption capacity at pH 7, 25 °C, and 1 ppm of arsenic concentration at equilibrium was 3.25, 1.45, and 1.65 mg As g−1 for F400-Fe (Filtrasorb 400 activated carbon), ACZ-Fe, and ACP-Fe (agave bagasse-based activated carbon produced by chemical activation with ZnCl2 and H3PO4), respectively. Vitela-Rodriguez and Rangel-Mendez (2013) modified different activated carbons with iron hydro(oxide) nanoparticles for arsenic adsorption from water. The surface areas of the modified activated carbons ranged from 632 to 1101 m2 g−1, and their maximum arsenic adsorption capacity varied from 370 to 1250 μg g−1. Temperature had no significant effect on arsenic adsorption; however, arsenic adsorption decreased
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32 % when the solution pH increased from 6 to 8. In addition, when groundwater was used in the experiments, the arsenic adsorption considerably decreased due to the presence of competing anions (mainly SO42−, Cl−, and F−) for active sites. The results of this study showed that iron-modified activated carbons are efficient adsorbents for arsenic at concentrations lower than 300 mg L−1. Gutierrez-Muñiz et al. (2013) obtained an iron-modified carbon (CFe) using pineapple crowns as the raw material. After the physical activation of carbon modified with iron nanoparticles, a second material, identified as iron carbide (CarFe), was obtained. The As(V) adsorption in both materials was affected by the time and arsenic concentration. The maximum As(V) uptake was 1.8 mg g−1 for CFe and 1.4 mg g−1 for CarFe. The results obtained indicated that both materials are equally useful for As(V) sorption. Yürüm et al. (2014) used α-Fe2O3 nanoparticles deposited on activated carbon to investigate As(V) adsorption capacity. Batch adsorption experiments showed high efficiency of As(V) removal and the maximum reported adsorption capacity was 27.78 mg g−1. The authors reported that more than 99.0 % of uptake was obtained within the pH range of 6–8. In this research, higher adsorption capacities compared to the research by Vitela-Rodriguez and Rangel-Mendez (2013) and Muñiz et al. (2009) were obtained, probably due to the treatment technique of adsorbent which is the microwave hydrothermal (MH) technique, but another important detail is that the used initial arsenic concentrations were higher than compared to the initial concentration of 20 mg L−1 in the study by Yürüm et al. (2014). Attia et al. (2014) prepared magnetic nanoparticle (γFe2O3)-coated zeolite (MNCZ) for arsenic ion removal from an aqueous solution. The obtained results showed that the MNCZ was effective for the removal of As from aqueous solutions, and the percentage removal of arsenic could reach over 95.6 % at a pH value of 2.5 within 15 min. Moreover, the removal of As depended on the initial arsenic concentration. For the regeneration of MNCZ material, 0.1 M NaOH was suitable for the desorption of As (70 % after 15 min), and the regenerated material showed an adsorption capacity of 93.95 % within five cycles. Carbon nanotubes and nanocomposites Carbon nanotubes (CNTs) To remove contaminants from water, or enrich metals from wastewater, CNTs and their composites have attracted great attention due to their excellent adsorption performance. The removal efficiency for metal ions by CNTs was observed between 10 and 80 %, which could be improved to approach 100 % by selectively functionalizing CNTs with organic ligands (Yu et al. 2014). Peng et al. (2005) developed ceria
supported on CNTs (CeO2-CNTs) adsorbent for arsenic removal from water. Under natural pH conditions, an increase from 0 to 10 mg L−1 in the concentration of Ca(II) and Mg(II) results in an increase from 10 to 81.9 and 78.8 mg g−1 in the amount of As(V) adsorbed, respectively. The adsorption was shown to be pH dependent. The efficient regeneration of the loaded adsorbent was carried out and an adsorption mechanism was suggested. Polymer nanocomposites The application of polymer-supported nanocomposites has been extensively explained in a recently published review article (Khin et al. 2012). Khin et al. (2012) emphasize the importance of polymeric adsorbents because of their high selectivity and adsorption capacity. There is a broad range of applications of polymer-supported nanomaterials depending on the target pollutant. For As(III) and As(V) removal, Khin et al. (2012) segregate hydrated ferric oxide nanoparticles where the polymer matrix is polymeric anion exchangers. Malana et al. (2011) synthesized aluminum-doped nanomanganese copper ferrite by chemical coprecipitation method and nanocomposite by doping this ferrite in methacrylate (MA), vinyl acetate (VA), and acrylic acid (AA) polymer through slow heating process for the removal of arsenic under neutral pH conditions. The equilibrium data was fitted to Freundlich, Langmuir, Dubinin-Radushkevich, and Flory Huggins models. The maximum adsorption capacity (qm) of arsenic on the nanocomposite was found to be 0.053 mg g−1 which was higher than that of many other adsorbents reported in the literature. Nanocomposite materials where iron nanoparticles were embedded into the walls of a macroporous polymer were produced and their efficiency for the As(III) removal from aqueous media was studied by Savina et al. (2011). Nanocomposite gels contained α-Fe2O3 and Fe3O4 nanoparticles and were prepared by cryopolymerization resulting in a monolithic structure with large interconnected pores up to 100 μm in diameter and possessing a high permeability (ca. 3 × 10−3 m s−1). The nanocomposite devices showed excellent capability for the removal of trace concentrations of As(III) from solution, with a total capacity of up to 3 mg As g−1 of nanoparticles. The leaching of iron was minimal and the device could operate in a pH range of 3–9 without diminishing removal efficiency. The effect of competing ions such as SO42− and PO43− was negligible. Vunain et al. (2013) observed from the kinetics that adsorption of As(III) ions onto polymer nanocomposites was very fast initially until equilibrium was reached. Nanocomposites proved to be the most effective for As(III) removal with 95.3 % removal at 26± 2 °C. Removal was pH dependent and the optimum pH for the removal of As(III) was found to be 8.6. Önnby et al. (2012) studied the removal of As(V) by adsorption from water solutions using three different synthetic
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adsorbents ((1) aluminum nanoparticles (Alu-NPs, <50 nm) incorporated in amine-rich cryogels (Alu-cryo), (2) molecular imprinted polymers (<38 μm) in polyacrylamide cryogels (MIP-cryo), and (3) thiol-functionalized cryogels (SH-cryo)). The particle incorporation increased the mechanical stability and the polymer backbones of pure polyacrylamide (MIPcryo) were of better stability than the amine containing polymer backbone (Alu-cryo). Both composites worked well in the studied pH range of 2–8. The adsorption of arsenic in real wastewater spiked with arsenic was, as expected, more reduced by co-ions (especially phosphate but also by sulfate and nitrate) than by counterions (copper and zinc) and more altered for Alu-cryo than for MIP-cryo. Both composites still adsorbed well in the presence of counterions (copper and zinc) present at low concentrations (μg L−1). This study showed that up to 100 % of As(V) was removed using Alu-NPs at pH 8, while about 95 % of all tested pH values was removed using SH-cryo and about 92 % using MIPs, so these materials can have potential as future adsorbent materials for As(V) removal in a full scale (Önnby et al. 2012). Saha and Sarkar (2012) developed an arsenic adsorbent comprising alumina nanoparticles dispersed in a polymer matrix and studied its adsorption characteristics. Alumina nanoparticles were prepared by reverse microemulsion technique and these were immobilized on chitosan-grafted polyacrylamide matrix by in situ dispersion. The removal was found to be pH dependent, and maximum removal was obtained at pH 7.2 when the equilibrium time was 6 h. The equilibrium adsorption data fitted very well with the Freundlich isotherm. The mechanism of arsenic removal by alumina-loaded polymer bead was governed by both electrostatic adsorptions and complexation. Since As(V) removal was optimum at pH 7.2, free amino group (–NH2) in CTS-g-PA might exist in equilibrium with the protonated amino group in acidic aqueous solution. Thus, arsenate ions might interact with the polymer through electrostatic interactions/complexation (protonated amino group) and hydrogen bonds (unprotonated amino group). The positively charged Al3+ at the surface of the biosorbent would attract negatively charged HAsO 4 − / H2AsO42− by electrostatic attraction. The regeneration study of the adsorbent resulted in retention of 94 % capacity in the fifth cycle. Graphite oxide nanocomposites nZVI has high adsorption capacity of As(III) and As(V), but it is limited in practical use due to its small particle size and aggregation effect (Wang et al. 2014). Reduced graphite oxide (RGO) has received intensive attention due to its exceptional electron transport, mechanical properties, and high surface area (Kim et al. 2010). Moreover, graphite oxide (GO) can be readily made from low-cost natural graphite in a large scale. Therefore, hybrid multifunctional materials based on
RGO were much more applicable than those based on pure nanomaterials. For this purpose, Luo et al. (2012) modified GO with Fe3O4 and MnO2 nanoparticles by a two-step coprecipitation. The good characteristics of this nanocomposite were due to the mixed effect of MnO2, high surface area of GO, and magnetic features of iron oxide. Maximum adsorption capacity according to Langmuir isotherm at pH 7 was 14.04 and 12.22 mg g−1 for both arsenic species. The MnO2 on the adsorbent surface promoted the oxidation of As(III) to As(V) without the addition of other oxidant. Since the pH plays a crucial role in the adsorption of contaminants, the Fe3O4-RGO-MnO2 nanocomposite remained stable in a pH range of 2–10. Other research conducted by Luo et al. (2013) showed that hydrated zirconium oxide (ZrO(OH)2) nanoparticles modified with graphene oxide (GO-ZrO(OH)2) had a high adsorption capacity in a wide pH range, and the monolayer adsorption amounts calculated based on the Langmuir adsorption model were 95.15 and 84.89 mg g−1 for As(III) and As(V), respectively, which were 3.54 and 4.64 times higher than that of ZrO(OH)2 nanoparticles. The high adsorption capacity was attributed to good dispersion of ZrO(OH)2 nanoparticles in the GO substrate. The concentration of 0.5 g L−1 GO-ZrO(OH)2 nanocomposites simultaneously removed As(III) and As(V) in water. Moreover, GO-ZrO(OH)2 showed good anti-interference ability to coexisting anions and exhibited excellent recyclability. In order to utilize the advantage of nZVI and RGO as well as to avoid the disadvantage of nZVI, Wang et al. (2014) loaded nZVI on RGO by chemical reactions. The adsorption capacities of As(III) and As(V), as determined from the Langmuir adsorption isotherms in batch experiments, were 35.83 and 29.04 mg g−1, respectively. The adsorption kinetics fitted well with the pseudo-second order model. The residual concentration was found to meet the standard of WHO after the samples were treated with 0.4 g L−1 nZVI-RGO when the initial concentrations of As(III) and As(V) were below 8 and 3 mg L−1. Especially, when the initial concentration of As(III) was below 3 mg L−1, the residual concentration was within 1 μg L−1, whereas the residual concentration was undetected when the initial concentration of As(III) was 1 mg L−1. Li et al. (2014) synthesized a monolithic Fe2O3/graphene hybrid directly by hydrothermal reaction of ferrous oxalate dehydrate and graphene oxide. The reduced graphene oxide formed an interconnected network structure that can be used as a support for homogenous distribution of active Fe2O3 nanoparticles. The authors stated that the graphene network and the pore channels in the hybrid facilitate fast electron transfer and ion transport so that the hybrid used as a selfsupported adsorbent can remove the As(V) concentration to far below 10 μg L−1 (initial arsenic concentration was 85 μg L−1). Due to its easy collection and excellent capability in removing As(V) from water, this adsorbent indicated a potential application in water purification.
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Perlite nanocomposite Nguyen Thanh et al. (2011) prepared composite adsorbents for As(V) removal from aqueous solution by incorporating αMnO2 (PM) nanorods and γ-Fe2O3 (PI) nanoparticles onto ball-milled expanded perlite carrier material. Arsenate maximum adsorption capacities of PM and PI were 7.09 and 4.64 mg g−1, respectively. An increase in As(V) adsorption capacity of PM and PI is a result of the physico-chemical properties of α-MnO2 nanorods and γ-Fe2O3 nanoparticles because of the improved specific surface area and adsorption affinity of the surface of the ball-milled expanded perlite. Biochar nanocomposite Zhang and Gao (2013b) produced biochar/AlOOH nanocomposite with nanosized polycrystalline AlOOH flakes on biochar surfaces. The adsorption equilibrium of As(V) on the nanocomposite was reached after 12 h. The kinetic data fits to the Elovich model very well. The result showed that the adsorption of As(V) on the nanocomposite was a heterogeneous process because the Elovich equation was originally developed to describe the kinetics of heterogeneous chemisorption. In addition, the Freundlich model worked better than the Langmuir model which is evident from the kinetic study that adsorption of As(V) on the biochar/AlOOH nanocomposite was controlled by heterogeneous processes. The Langmuir maximum capacity of biochar/AlOOH nanocomposite to As(V) was around 17,410 mg kg−1 which was greater than that of Al2O3 adsorbent and comparable to the reported value of activated Al2O3. Leaching of nanomaterials The leaching of sorbent components into the treated water is undesirable, and in most cases, there are no records on leaching of nanomaterials into water. However, for studying the applicability of the sorbents at a commercial scale, many studies on arsenic adsorption on leaching are required. The aim of the sorbent process is to avoid possible formation of not easy to capture submicrometer-sized particles and binding metal to sorbent to prevent metal leaching into the environment (Shan et al. 2009). Sharma and Sohn (2009) emphasize that phosphate, carbonate, and bicarbonate ions are efficient in inhibiting As adsorption and can increase As leaching from mineral surfaces. Pillewan et al. (2011) investigated the potability after water treatment and found that water quality remained unchanged except a slight change in pH and TDS. Accordingly, there was no leaching of copper during the treatment. Kumar et al. (2011) performed metal leaching for 6 h. The results showed that the iron content in some samples significantly increased (in APH_04 ~ 35 mg/g increased to 103 mg/g in the
PH22_BM_A), while the aluminum content in APH_40 was ~8.4 mg/g, which also increased to ~18 mg/g in the nanoparticles. Matei et al. (2011) examined leaching of Fe3O4 nanoparticles and Fe3O4 nanoparticle-covered dextran at different pH values (2.5, 6.5, and 8.5). The authors reported higher tendency of iron leaching from Fe3O4 nanoparticles than from Fe3O4 nanoparticle-covered dextran in all tested pH values. Significantly higher amounts of iron were detected from both tested adsorbents under highly acidic conditions (400 mg/g for Fe3O4 nanoparticles and 150 mg/g from Fe3O4 nanoparticlecovered dextran). Feng et al. (2012a) measured leaching of the synthesized ascorbic acid-coated Fe3O4 nanoparticles with different concentrations in As(III) aqueous solution of 0.12 mg L−1. Results showed that in all samples the concentrations of Fe ions were less than 0.1 mg L−1 which proved the high stability of this adsorbent. Gupta et al. (2011) examined arsenic leaching by the TCLP test. The results showed that the leached arsenic concentration in the used fluid (acetate buffer, pH=4.93± 0.05) was 0.02 (±0.01) mg L−1, which is 200 times lower than the U.S. EPA limit (U.S. EPA 1992), and the arsenic-rich solid could be marked as nonhazardous material. Further research by Gupta et al. (2012), evaluating chitosan zerovalent iron nanoparticles, proved that the concentration in the leachate was lower than 14 μg in the pH range of 2.9–6.3. An and Zhao (2012) stated that an As(III)-laden soil treated with carboxymethyl cellulose (CMC)-stabilized Fe-Mn could reduce the water leachable arsenic by 91–96 %, and the TCLP leachability was reduced by 94–98 %. Column elution tests revealed that application of CMC-stabilized Fe-Mn transferred nearly all water-soluble As(III) to the nanoparticle phase, and the nanoparticle amendment was able to reduce the TCLP leachability of As(III) remaining in the soil bed by 78 %. Zhang et al. (2013a) investigated leaching of Fe and Cu from the sorbent at different pH values. The Fe concentrations were all below 0.1 mg L−1, while leaching of Cu is serious under acid condition. However, its release is very small and the concentrations are still below the limit of 1 mg L−1. Also Luo et al. (2013) proved that the leaching of zirconyl ions from the adsorbents is negligible and the nanocomposite (GO-ZrO(OH)2) was stable during the arsenic adsorption test.
Conclusions Elevated levels of arsenic in surface and groundwater have been reported in many parts of the world. Therefore, the major global challenge of the twenty-first century is in providing clean and safe drinking water. Thus, the need for technological innovations and materials is important to keep up with the fast growing demand. It has been recognized that nanotechnology has a great potential in advancing water treatment and thereby
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improving water quality. Due to their large surface areas and their high adsorption capacities, nanomaterials are ideal in many applications such as membrane separation processes and adsorption. Additionally, nanomaterials can be functionalized with various chemical groups using different methods of modification to increase their efficiency of contaminant removal. Some author address the production cost of nanomaterials, but the focus is mostly on the cost-efficient techniques for removal of contaminants from water which can be achieved using cheaper materials. Nanoparticles for water treatment on a laboratory scale showed promising results, but it seems that for its full-scale application there are some hurdles which should be considered (i.e., costeffectiveness). This paper reviews the performances of various nanomaterials and nanobased adsorbents in arsenic removal citing papers on arsenic adsorption by nanomaterials which were recently published, mostly in the period between 2011 and 2014. It must be emphasized that most of these studies examined arsenic removal efficiencies of nanoparticles and nano-adsorbents via bench tests. Among all reviewed studies, the efficient arsenic removal and the highest adsorption capacities were achieved when water-soluble CMC-stabilized iron-manganese nanoparticles are used, although the authors emphasized the problem of their dispersibility in water when they are stabilized with CMC or starch. The maximum adsorption capacities of CMC-stabilized Fe-Mn nanoparticles were reported to be 338 mg g−1 for arsenite at pH 5.5 and 372 mg g−1 for arsenate at pH 3. The iron-based nanoparticles have also shown high capacities, especially at near neutral pH. Nano-zerovalent iron, which can be combined with other technologies such as Fenton and other processes, is frequently employed in arsenic removal from contaminated water, but there is a need for more detailed systematic studies on immobilization mechanism and also some technical improvements in preparing and utilizing nZVI. The most interesting feature of magnetic nanoparticles is their easy separation from the dissipated medium by magnetic force. For this purpose and because of their large surface areas, low toxicity, and price, magnetite and γ-Fe2O3 nanoparticles showed enhanced capacities for metal uptake in water treatment processes. However, the highest arsenic adsorption capacity is achieved by Fe3O4-magnetite nanoparticles at neutral pH (188.69 mg g−1 for As(III) and 153.8 mg g−1 for As(V)), while the lowest is noted when granulated activated carbons were impregnated with Fe2O3 (0.181 mg g−1 for As(V) at pH 7 and room temperature). Titanium nanoparticles have been successfully applied in combination with photooxidation processes for the remediation and/or treatment of groundwater and wastewater contaminated with toxic metals such as arsenic. The highest arsenite and arsenate adsorption capacities among titanium-based
nanoparticles demonstrated hydrous titanium dioxide (TiO2 · xH2O) (83 mg g−1 at neutral pH for arsenite and 96 mg g−1 at pH 9.0 for arsenate), while the lowest adsorption capacity shows the TiO2-impregnated chitosan beads used for arsenic removal at neutral pH and room temperature but without exposure to UV light (2.10 mg As(III) g−1 and 2.05 mg As(V) g−1). Very high arsenic adsorption capacities are also achieved when some other metal-based nanoparticles were used for arsenic remediation. Study results revealed very high adsorption capacities at neutral pH of hydrous cerium oxide (170 mg g−1 for As(III) and 107 mg g−1 for As(V)), while the smallest amounts of arsenic are remediated with nanoadsorbent synthesized by biological silver reduction (maximum arsenate adsorption capacity of 0.975 mg g−1). Most mixed oxide nanoparticles show good performances, and adsorption capacities at neutral pH ranges from 127.4 mg g−1 for As(III) and 83.2 mg g−1 As(V) reported for superparamagnetic ultrafine magnesium ferrite (Mg0.27Fe2.50O4) nanoadsorbent to 2.89 mg g−1 for As(III) and 3.84 mg g−1 for As(V) reported for the mixture of Fe2O3/MnO2 were reported. Another efficient water contaminant removal agent which has attracted great attention in the last few years is carbon nanotubes and their composites. Given their excellent adsorption conditions, CNTs possess high sensitivity and selectivity toward the enrichment of metals or detection of toxic metal pollution of the environment, and for this purpose, they are highly employed in the removal of metal ions from water. It is well known that CNTs are not easy to remove from the adsorbed solutions, but the application of CNTs-based magnetic hybrids solves this issue. Modified activated carbons and zeolites enriched with iron nanoparticles revealed much higher adsorption capacities for heavy metals. Impregnation of metal nanoparticles into granulated adsorbents creates much broader implications related to the contaminant removal than the sole improvements related to arsenic removal. Carbon nanotubes and nanocomposites are also potentially good arsenic adsorbents since they usually possess high adsorption capacities. Among them, the highest arsenic adsorption capacities show hydrated zirconium oxide (ZrO(OH)2) nanoparticles modified with graphene oxide (GO-ZrO(OH)2), 95.15 mg g−1 for As(III) and 84.89 mg g−1 for As(V) both obtained at pH 7 and room temperature, respectively. The lowest arsenic adsorption capacity within the reviewed nanotubes and nanocomposites of 0.053 mg g−1 shows aluminumdoped nanomanganese copper ferrite nanocomposite. Compared with all the abovementioned nanoparticles and nano-adsorbents, significantly lowest adsorption capacities are reported when modified activated carbons or zeolites are used for arsenic remediation. The maximum adsorption capacities varied from 27.78 mg g−1 reported when arsenic was removed from model solution at pH 7 and room
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temperature using activated carbon saturated with α-Fe2O3 nanoparticles to 0.036 mg g−1 reported when Fe in the form of nanoparticles was doped on activated carbon. It has to be emphasized that most of the authors did not report on the obtained residual arsenic concentrations and whether these concentrations meet the regulation limit of 10 μg L−1 which would be the absolute criteria for a reliable comparison. Finally, future arsenic removal studies using nanoparticles and nanobased adsorbents, besides their efficiencies, should also consider the cost of their application in real conditions of water treatment plants, as well as reducing the disposal of arsenic treatment waste. This will help in revealing the whole picture of nanoparticles in the environment which demands a close collaboration between research institutions, industries, and governments. Acknowledgments The authors are very grateful to Dr. Andrew Flanagan, PhD, for English proofreading. The authors wish to thank the anonymous reviewers whose comments and suggestions have significantly improved the quality of this manuscript. This research was done as part of the project BArsenic removal from water using nanoparticlefunctionalized adsorbents^ supported by the Josip Juraj Strossmayer University of Osijek.
References Akin I, Arslan G, Tor A, Ersoz M, Cengeloglu Y (2012) Arsenic(V) removal from underground water by magnetic nanoparticles synthesized from waste red mud. J Hazard Mater 235–236:62–68 Ambashta RD, Sillanpää M (2010) Water purification using magnetic assistance: a review. J Hazard Mater 180:38–49 An B, Zhao D (2012) Immobilization of As(III) in soil and groundwater using a new class of polysaccharide stabilized Fe–Mn oxide nanoparticles. J Hazard Mater 211–212:332–341 Andjelkovic I, Nesic J, Stankovic D, Manojlovic D, Pavlovic MB, Jovalekic C, Roglic G (2014) Investigation of sorbents synthesised by mechanical–chemical reaction for sorption of As(III) and As(V) from aqueous medium. Clean Techn Environ Policy 16:395–403 Attia TMS, Hu XL, Qiang (2014) Synthesized magnetic nanoparticles coated zeolite (MNCZ) for the removal of arsenic (As) from aqueous solution. J Exp Nanosci 9(6):551–560 Basu T, Ghosh UC (2011) Arsenic(III) removal performances in the absence/presence of groundwater occurring ions of agglomerated Fe(III)-Al(III) mixed oxide nanoparticles. J Ind Eng Chem 17: 834–844 Basu T, Ghosh UC (2013) Nano-structured iron(III)-cerium(IV) mixed oxide: synthesis, characterization and arsenic sorption kinetics in the presence of co-existing ions aiming to apply for high arsenic groundwater treatment. Appl Surf Sci 283:471–481 Bezbaruah AN, Kalita H, Almeelbi T, Capecchi CL, Jacob DL, Ugrinov AG, Payne SA (2013) Ca-alginate-entrapped nanoscale iron: arsenic treatability and mechanism studies. J Nanopart Res 16:2175 Bhowmick S, Chakraborty S, Mondal P, Van Renterghem W, Van den Berghe S, Roman-Ross G, Chatterjee D, Iglesias M (2014) Montmorillonite-supported nanoscale zero-valent iron for removal of arsenic from aqueous solution: kinetics and mechanism. Chem Eng J 243:14–23
Bilici Baskan M, Pala A (2010) A statistical experiment design approach for arsenic removal by coagulation process using aluminum sulfate. Desalination 254:42–48 Bujňáková Z, Baláž P, Zorkovská A, Sayagués MJ, Kováč J, Timko M (2013) Arsenic sorption by nanocrystalline magnetite: an example of environmentally promising interface with geosphere. J Hazard Mater 262:1204–1212 Chammui Y, Sooksamiti P, Naksata W, Thiansem S, Arqueropanyo O-A (2014) Removal of arsenic from aqueous solution by adsorption on Leonardite. Chem Eng J 240:202–210 Chen MD (2004) Effects of nanophase materials (<=20 nm) on biological responses. J Environ Sci Health A 39(10):2691–2705 Chen R, Zhi C, Yang H, Bando Y, Zhang Z, Sugiur N, Golberg D (2011) Arsenic(V) adsorption on Fe3O4 nanoparticle-coated boron nitride nanotubes. J Colloid Interface Sci 359:261–268 Chowdhury SR, Yanful EK (2011) Arsenic removal from aqueous solutions by adsorption on magnetite nanoparticles. Water Environ J 25: 429–437 Chowdhury SR, Yanful EK (2010) Arsenic and chromium removal by mixed magnetite-maghemite nanoparticles and the effect of phosphate on removal. J Environ Manag 91:2238–2247 Chowdhury SR, Yanful EK, Pratt AR (2011) Arsenic removal from aqueous solutions by mixed magnetite–maghemite nanoparticles. Environ Earth Sci 64:411–423 Cooper AM, Hristovski KD, Möller T, Westerhoff P, Sylvester P (2010) The effect of carbon type on arsenic and trichloroethylene removal capabilities of iron (hydr)oxide nanoparticle-impregnated granulated activated carbons. J Hazard Mater 183:381–388 Cui H, Li Q, Gao S, Shang JK (2012) Strong adsorption of arsenic species by amorphous zirconium oxide nanoparticles. J Ind Eng Chem 18: 1418–1427 Cui H, Su Y, Li Q, Gao S, Shang JK (2013) Exceptional arsenic (III, V) removal performance of highly porous, nanostructured ZrO2 spheres for foxed bed reactors and the full-scale system modeling. Water Res 47:6258–6268 Ćavar S, Klapec T, Jurišić Grubešić R, Valek M (2005) High exposure to arsenic from drinking water at several localities in eastern Croatia. Sci Total Environ 339:277–282 Dong H, Guan X, Lo IMC (2012) Fate of As(V)-treated nano zero-valent iron: determination of arsenic desorption potential under varying environmental conditions by phosphate extraction. Water Res 46: 4071–4080 Faria MCS, Rosemberg RS, Bomfeti CA, Monteiro DS, Barbosa F, Oliveira LCA, Rodriguez M, Pereira MC, Rodrigues JL (2014) Arsenic removal from contaminated water by ultrafine δ-FeOOH adsorbents. Chem Eng J 237:47–54 Feng L, Cao M, Ma X, Zhu Y, Hu C (2012a) Superparamagnetic highsurface-area Fe3O4 nanoparticles as adsorbents for arsenic removal. J Hazard Mater 217–218:439–446 Feng Q, Zhang Z, Ma Y, He X, Zhao Y, Chai Z (2012b) Adsorption and desorption characteristics of arsenic onto ceria nanoparticles. Nanoscale Res Lett 7:84 Fierro V, Muñiz G, Gonzalez-Sánchez G, Ballinas ML, Celzard A (2009) Arsenic removal by iron-doped activated carbons prepared by ferric chloride forced hydrolysis. J Hazard Mater 168:430–437 Flicklin WH (1983) Separation of arsenic(III) and arsenic(V) in ground waters by ion-exchange. Talanta 30:371–373 Fu F, Dionysiou DD, Liu H (2014) The use of zero-valent iron for groundwater remediation and wastewater treatment: a review. J Hazard Mater 267:194–205 Gebel TW (1999) Arsenic and drinking water contamination. Science 283:1458–1459 Ghosh MK, Poinern GEJ, Issa TB, Singh P (2012) Arsenic adsorption on goethite nanoparticles produced through hydrazine sulfate assisted synthesis method. Korean J Chem Eng 29(1):95–102
Environ Sci Pollut Res Goswami A, Raul PK, Purkait MK (2012) Arsenic adsorption using copper(II) oxide nanoparticles. Chem Eng Res Des 90:1387–1396 Guan XH, Ma J, Dong HR, Jiang L (2009) Removal of arsenic from water: effect of calcium ions on As(III) removal in the KMnO4Fe(III) process. Water Res 43:5119–5128 Guan X, Du J, Meng X, Sun Y, Sun B, Hu Q (2012) Application of titanium dioxide in arsenic removal from water: a review. J Hazard Mater 215–216:1–16 Gupta A, Yunus M, Sankararamakrishnan N (2012) Zerovalent iron encapsulated chitosan nanospheres—a novel adsorbent for the removal of total inorganic arsenic from aqueous systems. Chemosphere 86:150–155 Gupta K, Maity A, Ghosh UC (2010) Manganese associated nanoparticles agglomerate of iron(III) oxide: synthesis, characterization and arsenic(III) sorption behavior with mechanism. J Hazard Mater 184: 832–842 Gupta K, Bhattacharya S, Chattopadhyay D, Mukhopadhyay A, Biswas H, Dutta J, Ray NR, Ghosh UC (2011) Ceria associated manganese oxide nanoparticles: synthesis, characterization and arsenic(V) sorption behavior. Chem Eng J 172:219–229 Gutierrez-Muñiz OE, García-Rosales G, Ordoñez-Regil E, Olguin MT, Cabral-Prieto A (2013) Synthesis, characterization and adsorptive properties of carbon with iron nanoparticles and iron carbide for the removal of As(V) from water. J Environ Manag 114:1–7 He F, Zhao D (2005) Preparation and characterization of a new class of starch-stabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons in water. Environ Sci Technol 39:3314–3320 Hristovski K, Baumgardner A, Westerhoff P (2007) Selecting metal oxide nanomaterials for arsenic removal in fixed bed columns: from nanopowders to aggregated nanoparticles media. J Hazard Mater 147(1–2):265–274 Jain CK, Ali I (2000) Arsenic: Occurrence, toxicity and speciation techniques. Water Res 34(17):4304–4312 Jegadeesan G, Al-Abed SA, Sundaram V, Choi H, Scheckel KG, Dionysiou DD (2010) Arsenic sorption on TiO2 nanoparticles: size and crystallinity effects. Water Res 44:965–973 Jekel RM (1994) Removal of arsenic in drinking water treatment, removal of arsenic in drinking water treatment. Arsenic in the environment: part 1: cycling and characterization. Wiley, New York Jézéquel H, Chu KH (2005) Enhanced adsorption of arsenate on titanium dioxide using Ca and Mg ions. Environ Chem Lett 3:132–135 Jin Y, Liu F, Tong M, Hou Y (2012) Removal of arsenate by cetyltrimethylammonium bromide modified magnetic nanoparticles. J Hazard Mater 227–228:461–468 Jing C, Meng X (2009) Nanotechnologies for water environment applications. ASCE Publications, Virginia Kanel SR, Manning B, Charlet L, Choi H (2005) Removal of arsenic(III) from groundwater by nanoscale zero-valent iron. Environ Sci Technol 39:1291–1298 Katsoyiannis IA, Zouboulis AI (2002) Removal of arsenic from contaminated water sources by sorption onto iron-oxide-coated polymeric materials. Water Res 36:5141–5155 Khan MMT, Yamamoto K, Ahmed MF (2002) A low cost technique of arsenic removal from drinking water by coagulation using ferric chloride salt and alum. Water Sci Technol Water Supply 2:281–288 Khin MM, Nair AS, Babu VJ, Murugan R, Ramakrishna S (2012) A review on nanomaterials for environmental remediation. Energy Environ Sci 5:8075–8109 Kilianová M, Prucek R, Filip J, Kolařík J, Kvítek L, Panáček A, Tuček J, Z b o ř i l R ( 2 0 1 3 ) R e m a r k a b l e e ff i c i e n c y o f u l t r a f i n e superparamagnetic iron(III) oxide nanoparticles toward arsenate removal from aqueous environment. Chemosphere 93:2690–2697 Kim H, Abdala AA, Macosko CW (2010) Graphene/polymer nanocomposites. Macromolecules 43(16):6515–6530 Korte NE, Fernando Q (1991) A review of arsenic(III) in groundwater. Crit Rev Environ Control 211:1–39
Klimkova S, Cernik M, Lacinova L, Filip J, Jancik D, Zboril R (2011) Zero-valent iron nanoparticles in treatment of acid mine water from in situ uranium leaching. Chemosphere 82:1178–1184 Kumar V, Talreja N, Deva D, Sankararamakrishnan N, Sharma A, Verma N (2011) Development of bi-metal doped micro- and nano multifunctional polymeric adsorbents for the removal of fluoride and arsenic(V) from wastewater. Desalination 282:27–38 Li L, Zhou G, Wang Z, Shan X-Y, Li F, Cheng H-M (2014) Monolithic Fe2O3/graphene hybrid for highly efficient lithium storage and arsenic removal. Carbon 67:500–507 Li R, Li Q, Gao S, Shang JK (2012a) Exceptional arsenic adsorption performance of hydrous cerium oxide nanoparticles: part A. Adsorption capacity and mechanism. Chem Eng J 185–186:127– 135 Li X-q, Elliott DW, W-x Z (2006) Zero-valent iron nanoparticles for abatement of environmental pollutants: materials and engineering aspects. Crit Rev Solid State 31:111–122 Li Y, Liu JR, Jia SY, Guo JW, Zhuo J, Na P (2012b) TiO2 pillared montmorillonite as a photoactive adsorbent of arsenic under UV irradiation. Chem Eng J 191:66–74 Liang Q, An B, Zhao D (2013) Removal and immobilization of arsenic in water and soil using polysaccharide-modified magnetite nanoparticles, monitoring water quality. Pollution assessment, analysis, and remediation. Elsevier, Waltham Lin TF, Wu JK (2001) Adsorption of arsenite and arsenate within activated alumina grains: equilibrium and kinetics. Water Res 35:2049– 2057 Lin S, Lu D, Liu Z (2012) Removal of arsenic contaminants with magnetic γ-Fe2O3 nanoparticles. Chem Eng J 211–212:46–52 Litter MI, Morgada ME, Bundschuh J (2010) Possible treatments for arsenic removal in Latin American waters for human consumption. Environ Pollut 158:1105–1118 Lunge S, Singh S, Sinha A (2014) Magnetic iron oxide (Fe3O4) nanoparticles from tea waste for arsenic removal. J Magn Magn Mater 356: 21–31 Luo X, Wang C, Luo S, Dong R, Tu X, Zeng G (2012) Adsorption of As(III) and As(V) from water using magnetite Fe3O4-reduced graphite oxide-MnO2 nanocomposites. Chem Eng J 187:45–52 Luo X, Wang C, Wang L, Deng F, Luo S, Tu X, Au C (2013) Nanocomposites of graphene oxide-hydrated zirconium oxide for simultaneous removal of As(III) and As(V) from water. Chem Eng J 220:98–106 Luther S, Borgfeld N, Kim J, Parsons JG (2012) Removal of arsenic from aqueous solution: a study of the effects of pH and interfering ions using iron oxide nanomaterials. Microchem J 101:30–36 Mahmood I, Lopes CB, Lopes I, Ahmad I, Duarte AC, Pereira E (2013) Nanoscale materials and their use in water contaminants removal—a review. Environ Sci Pollut Res 20:1239–1260 Malana MA, Qureshi RB, Ashiq MN (2011) Adsorption studies of arsenic on nanoaluminium doped manganese copper ferrite polymer (MA, VA, AA) composite: kinetics and mechanism. Chem Eng J 172:721–727 Mak MSH, Rao P, Lo IMC (2009) Effects of hardness and alkalinity on the removal of arsenic(V) from humic acid-deficient and humic acid-rich groundwater by zero-valent iron. Water Res 43:4296–4304 Martinson CA, Reddy KJ (2009) Adsorption of arsenic(III) and arsenic(V) by cupric oxide nanoparticles. J Colloid Interface Sci 336:406–411 Matei E, Predescu C, Berbecaru A, Predescu A, Truşcă (2011) Leaching tests for synthesized magnetite nanoparticles used as adsorbent for metal ions from liquid solutions. Dig J Nanomater Bios 6(4):1701– 1708 Miller SM, Zimmerman JB (2010) Novel, bio-based, photoactive arsenic sorbent: TiO2-impregnated chitosan bead. Water Res 44:5722–5729
Environ Sci Pollut Res Miller SM, Spaulding ML, Zimmerman JB (2011) Optimization of capacity and kinetics for a novel bio based arsenic sorbent, TiO2-impregnated chitosan bead. Water Res 45:5745–5754 Mondal P, Bhowmick S, Chatterjee D, Figoli A, Van der Bruggen, B (2013) Remediation of inorganic arsenic in groundwater for safe water supply: a critical assessment of technological solutions. Chemosphere, 92:157–170 Mohan D, Pittman CU Jr (2007) Arsenic removal from water/wastewater using adsorbents—a critical review. J Hazard Mater 142:1–53 Monárez-Cordero B, Amézaga-Madrid P, Antúnez-Flores W, LeyvaPorras C, Pizá-Ruiz P, Miki-Yoshida M (2014) Highly efficient removal of arsenic metal ions with high superficial area hollow magnetite nanoparticles synthetized by AACVD method. J Alloys Compd 586:S520–S525 Morgada ME, Levy IK, Salomone V, Farías SS, López G, Litter MI (2009) Arsenic(V) removal with nanoparticulate zerovalent iron: effect of UV light and humic acids. Catal Today 143:261–268 Mólgora CC, Domínguez AM, Avila EM, Drogui P, Buelna G (2013) Removal of arsenic from drinking water: a comparative study between electrocoagulation-microfiltration and chemical coagulationmicrofiltration processes. Sep Purif Technol 118:645–651 Muñiz G, Fierro V, Celzard A, Furdin G, Gonzalez-Sánchez G, Ballinas ML (2009) Synthesis, characterization and performance in arsenic removal of iron-doped activated carbons prepared by impregnation with Fe(III) and Fe(II). J Hazard Mater 165:893–902 Nabi D, Aslam I, Qazi IA (2009) Evaluation of the adsorption potential of titanium dioxide nanoparticles for arsenic removal. J Environ Sci 21: 402–408 Ng JC, Wang J, Shraim A (2003) A global health problem caused by arsenic from natural sources. Chemosphere 52:1353–1359 Nguyen Thanh D, Singh M, Ulbrich P, Strnadova N, Štěpánek F (2011) Perlite incorporating γ-Fe2O3 and α-MnO2 nanomaterials: preparation and evaluation of a new adsorbent for As(V) removal. Sep Purif Technol 82:93–101 Nieto-Delgado C, Rangel-Mendez JR (2012) Anchorage of iron hydro(oxide) nanoparticles onto activated carbon to remove As(V) from water. Water Res 46:2973–2982 Ning RY (2002) Arsenic removal by reverse osmosis. Desalination 143: 237–241 Nowack B (2008) Pollution prevention and treatment using nanotechnology, nanotechnology. Volume 2: environmental aspects. Wiley, Weinheim Olyaie E, Banejad H, Afkhami A, Rahmani A, Khodaveisi J (2012) Development of a cost-effective technique to remove the arsenic contamination from aqueous solutions by calcium peroxide nanoparticles. Sep Purif Technol 95:10–15 Önnby L, Pakade V, Mattiasson B, Kirsebom H (2012) Polymer composite adsorbents using particles of molecularly imprinted polymers or aluminium oxide nanoparticles for treatment of arsenic contaminated waters. Water Res 46:4111–4120 Özlem Kocabaş-Ataklı Z, Yürüm Y (2013) Synthesis and characterization of anatase nanoadsorbent and application in removal of lead, copper and arsenic from water. Chem Eng J 225:625–635 Pal P, Chakrabortty S, Linnanen L (2014) A nanofiltration–coagulation integrated system for separation and stabilization of arsenic from groundwater. Sci Total Environ 476–477:601–610 Patel HA, Byun J, Yavuz CT (2012) Arsenic removal by magnetic nanocrystalline barium hexaferrite. J Nanopart Res 14:881 Patra AK, Dutta A, Bhaumik A (2012) Self-assembled mesoporous γAl2O3 spherical nanoparticles and their efficiency for the removal of arsenic from water. J Hazard Mater 201–202:170–177 Pena M, Korfiatis GP, Patel M, Lippincott L, Meng X (2005) Adsorption of As(V) and As(III) by nanocrystalline titanium dioxide. Water Res 39(11):2327–2337
Peng X, Luan Z, Ding J, Di Z, Li Y, Tian B (2005) Ceria nanoparticles supported on carbon nanotubes for the removal of arsenate from water. Mater Lett 59:399–403 Pillewan P, Mukherjee S, Roychowdhury T, Das S, Bansiwal A, Rayalu S (2011) Removal of As(III) and As(V) from water by copper oxide incorporated mesoporous alumina. J Hazard Mater 186:367–375 Pirilä M, Martikainen M, Ainassaari K, Kuokkanen T, Keiski RL (2011) Removal of aqueous As(III) and As(V) by hydrous titanium dioxide. J Colloid Interface Sci 353:257–262 Prasad B, Ghosh C, Chakraborty A, Bandyopadhyay N, Ray RK (2011) Adsorption of arsenite (As3+) on nano-sized Fe2O3 waste powder from the steel industry. Desalination 274:105–112 Prasse C, Ternes T (2010) Removal of organic and inorganic pollutants and pathogens from wastewater and drinking water using nanoparticles—a review. Nanoparticles in the water cycle. Springer, Berlin Qu X, Alvarez PJJ, Li Q (2013a) Applications of nanotechnology in water and wastewater treatment. Water Res 47:3931–3946 Qu X, Brame J, Li Q, Alvarez PJJ (2013b) Nanotechnology for a safe and sustainable water supply: enabling integrated water treatment and reuse. Acc Chem Res 46(3):834–843 Ramos MAV, Yan W, X-q L, Koel BE, W-x Z (2009) Simultaneous oxidation and reduction of arsenic by zero-valent iron nanoparticles: understanding the significance of the core-shell structure. J Phys Chem C 113:14591–14594 Reddy KJ, McDonald KJ, King H (2013) A novel arsenic removal process for water using cupric oxide nanoparticles. J Colloid Interf Sci 397:96–102 Romić Ž, Habuda-Stanić M, Kalajdžić B, Kuleš M (2011) Arsenic distribution, concentration and speciation in groundwater of the Osijek area, eastern Croatia. Appl Geochem 26:37–44 Rowland HAL, Omoregie EO, Millot R, Jimenez C, Mertens J, Baciu C, Hug SJ, Berg M (2011) Geochemistry and arsenic behavior in groundwater resources of the Pannonian Basin (Hungary and Romania). Appl Geochem 26:1–17 Saha S, Sarkar P (2012) Arsenic remediation from drinking water by synthesized nano-alumina dispersed in chitosan-grafted polyacrylamide. J Hazard Mater 227–228:68–78 Sahiner N, Ozay O, Aktas N, Blake DA, John VT (2011) Arsenic (V) removal with modifiable bulk and nano p(4-vinylpyridine)-based hydrogels: the effect of hydrogel sizes and quarternization agents. Desalination 279:344–352 Saikia J, Saha B, Das G (2011) Efficient removal of chromate and arsenate from individual and mixed system by malachite nanoparticles. J Hazard Mater 186:575–582 Sandoval R, Cooper AM, Aymar K, Jain A, Hristovski K (2011) Removal of arsenic and methylene blue from water by granular activated carbon media impregnated with zirconium dioxide nanoparticles. J Hazard Mater 193:296–303 Savage N, Diallo MS (2005) Nanomaterials and water purification: opportunities and challenges. J Nanopart Res 7:331–342 Savina IN, English CJ, Whitby RLD, Zheng Y, Leistner A, Mikhalovsky SV, Cundy AB (2011) High efficiency removal of dissolved As(III) using iron nanoparticle-embedded macroporous polymer composites. J Hazard Mater 192:1002–1008 Selvakumar R, Arul Jothi N, Jayavignesh V, Karthikaiselvi K, Immanual Antony G, Sharmila PR, Kavitha S, Swaminathan K (2011) As(V) removal using carbonized yeast cells containing silver nanoparticles. Water Res 45:583–592 Shan C, Tong M (2013) Efficient removal of trace arsenite through oxidation and adsorption by magnetic nanoparticles modified with FeMn binary oxide. Water Res 47:3411–3421 Shan G, Surampalli RY, Tyagi RD, Zhang TC (2009) Nanomaterials for environmental burden reduction, waste treatment, and nonpoint source pollution control: a review. Front Environ Sci Eng China 3(3):249–264
Environ Sci Pollut Res Sharma YC, Srivastava V, Singh VK, Kaul SN, Weng CH (2009) Nano‐ adsorbents for the removal of metallic pollutants from water and wastewater. Environ Technol 30(6):583–609 Sharma A, Verma N, Sharma A, Deva D, Sankararamakrishnan N (2010) Iron doped phenolic resin based activated carbon micro and nanoparticles by milling: synthesis, characterization and application in arsenic removal. Chem Eng Sci 65:3591–3601 Sharma VK, Sohn M (2009) Aquatic arsenic: toxicity, speciation, transformations, and remediation. Environ Int 35:743–759 Shih MC (2005) An overview of arsenic removal by pressure-driven membrane process. Desalination 172:85–97 Shipley HJ, Engates KE, Guettner AM (2011) Study of iron oxide nanoparticles in soil for remediation of arsenic. J Nanopart Res 13:2387– 2397 Shipley HJ, Yean S, Kan AT, Tomson MB (2009) Adsorption of arsenic to magnetite nanoparticles: effect of particle concentration, pH, ionic strength, and temperature. Environ Toxicol Chem 28(3):509–515 Shipley HJ, Yean S, Kan AT, Tomson MB (2010) A sorption kinetics model for arsenic adsorption to magnetite nanoparticles. Environ Sci Pollut Res 17:1053–1062 Shwe WM, Oo MM, Hlaing SS (2012) Preparation of iron oxide nanoparticles mixed with calcinated laterite for arsenic removal, International Conference on Chemical Engineering and its Applications (ICCEA’2012) September 8-9. Bangkok, Thailand Simeonidis K, Gkinis T, Tresintsi S, Martinez-Boubeta C, Vourlias G, Tsiaoussis I, Stavropoulos G, Mitrakas M, Angelakeris M (2011) Magnetic separation of hematite-coated Fe3O4 particles used as arsenic adsorbents. Chem Eng J 168:1008–1015 Smedley PL, Kinniburg DG (2002) A review of the source, behavior and distribution of arsenic in natural waters. Appl Geochem 17:517–568 Song K, Kim W, Suh C-Y, Shin D, Ko K-S, Ha K (2013) Magnetic iron oxide nanoparticles prepared by electrical wire explosion for arsenic removal. Powder Technol 246:572–574 Sun W, Li Q, Gao S, Shang JK (2012) Exceptional arsenic adsorption performance of hydrous cerium oxide nanoparticles: part B. Integration with silica monoliths and dynamic treatment. Chem Eng J 185:136–143 Tajuddin Sikder M, Tanaka S, Saito T, Kurasaki M (2014) Application of zerovalent iron impregnated chitosan-carboxymethyl-βcyclodextrin composite beads as arsenic sorbent. J Environ Chem Eng 2:370–376 Tanboonchuy V, Grisdanurak N, Liao C-H (2012) Background species effect on aqueous arsenic removal by nano zero-valent iron using fractional factorial design. J Hazard Mater 205–206:40–46 Tandon PK, Shukla RC, Singh SB (2013) Removal of arsenic(III) from water with clay-supported zerovalent iron nanoparticles synthesized with the help of tea liquor. Ind Eng Chem Res 52:10052–10058 Tang SCN, Lo IMC (2013) Magnetic nanoparticles: essential factors for sustainable environmental applications. Water Res 47:2613–2632 Tang W, Li Q, Gao S, Shang JK (2011a) Arsenic (III, V) removal from aqueous solution by ultrafine α-Fe2O3 nanoparticles synthesized from solvent thermal method. J Hazard Mater 192:131–138 Tang W, Li Q, Li C, Gao S, Shang JK (2011b) Ultrafine α-Fe2O3 nanoparticles grown in confinement of in situ self-formed Bcage^ and their superior adsorption performance on arsenic(III). J Nanopart Res 13:2641–2651 Tang W, Su Y, Li Q, Gao S, Shang JK (2013) Superparamagnetic magnesium ferrite nanoadsorbent for effective arsenic (III, V) removal and easy magnetic separation. Water Res 47:3624–3634 Tresintsi S, Simeonidis K, Pliatsikas N, Vourlias G, Patsalas P, Mitrakas M (2014) The role of SO42− surface distribution in arsenic removal by iron oxy-hydroxides. J Solid State Chem 213:145–151 Tresintsi S, Simeonidis K, Vourlias G, Stavropoulos G, Mitrakas M (2012) Kilogram-scale synthesis of iron oxy-hydroxides with improved arsenic removal capacity: study of Fe(II) oxidationprecipitation parameters. Water Res 46:5255–5267
Tresintsi S, Simeonidis K, Estradé S, Martinez-Boubeta C, Vourlias G, Pinakidou F, Katsikini M, Paloura EC, Stavropoulos G, Mitrakas M (2013) Tetravalent manganese feroxyhyte: a novel nanoadsorbent equally selective for As(III) and As(V) removal from drinking water. Environ Sci Technol 47:9699–9705 Tuutijärvi T, Lu J, Sillanpää M, Chen G (2009) As(V) adsorption on maghemite nanoparticles. J Hazard Mater 66:1415–1420 Van Dorn D, Ravalli MT, Small MM, Hillery B, Andreescu S (2011) Adsorption of arsenic by iron oxide nanoparticles: a versatile, inquiry-based laboratory for a high school or college science course. J Chem Educ 88:1119–1122 Van Halem D (2011) Subsurface Iron and Arsenic Removal for drinking water treatment in Bangladesh Water Management Academic Press, Delft Vaclavikova M, Gallios G, Stefusova K, Jakabsky S, Hredzak S (2008) Application of Fe-nanoscale materials useful in the removal of arsenic from waters, functionalized nanoscale materials, devices and systems. Springer, Dordrecht Vitela-Rodriguez AV, Rangel-Mendez JR (2013) Arsenic removal by modified activated carbons with iron hydro(oxide) nanoparticles. J Environ Manag 114:225–231 Vunain E, Mishra AK, Krause RW (2013) Fabrication, characterization and application of polymer nanocomposites for arsenic(III) removal from water. J Inorg Organomet Polym 23:293–305 Wang C, Luo H, Zhang Z, Wu Y, Zhang J, Chen S (2014) Removal of As(III) and As(V) from aqueous solutions using nanoscale zero valent iron-reduced graphite oxide modified composites. J Hazard Mater 268:124–131 Wickramasinghe SR, Han B, Zimbron J, Shen Z, Karim MN (2004) Arsenic removal by coagulation and filtration: comparison of ground waters from the United States and Bangladesh. Desalination 169:231–244 World Health Organization, WHO (2001) Environmental health criteria 224: arsenic and arsenic compounds, 2nd edn. WHO, Geneva World Health Organization, WHO (2011) Guidelines for drinking-water quality, 4th edn. World Health Organization, Geneva Xu P, Zeng GM, Huang DL, Feng CL, Hu S, Zhao MH, Lai C, Wei Z, Huang C, Xie GX, Liu ZF (2012) Use of iron oxide nanomaterials in wastewater treatment: a review. Sci Tot Environ 424:1–10 Xu W, Wang J, Wang L, Sheng G, Liu J, Yu H, Huang X-J (2013) Enhanced arsenic removal from water by hierarchically porous CeO2–ZrO2 nanospheres: role of surface- and structure-dependent properties. J Hazard Mater 260:498–507 Xu Z, Li Q, Gao S, Shang JK (2010) As(III) removal by hydrous titanium dioxide prepared from one-step hydrolysis of aqueous TiCl4 solution. Water Res 44:5713–5721 Yan W, Ramos MAV, Koel BE, W-x Z (2010) Multi-tiered distributions of arsenic in iron nanoparticles: observation of dual redox functionality enabled by a core–shell structure. Chem Commun 46:6995–6997 Yang W, Kan AT, Chen W, Tomson MB (2010) pH-dependent effect of zinc on arsenic adsorption to magnetite nanoparticles. Water Res 44: 5693–5701 Yantasee W, Warner CL, Sangvanich T, Addleman RS, Carter TG, Wiacek RJ, Frywell GE, Timchalk C, Warner MG (2007) Removal of heavy metals from aqueous systems with thiol functionalized superparamagnetic nanoparticles. Environ Sci Technol 4: 5114–5119 Yamani JS, Miller SM, Spaulding ML, Zimmerman JB (2012) Enhanced arsenic removal using mixed metal oxide impregnated chitosan beads. Water Res 46:4427–4434 Yu J-G, Zhao X-H, Yu L-Y, Jiao F-P, Jiang J-H, Chen X-Q (2014) Removal, recovery and enrichment of metals from aqueous solutions using carbon nanotubes. J Radioanal Nucl Chem 299:1155– 1163 Yu L, Peng X, Ni F, Li J, Wang D, Luan Z (2013a) Arsenite removal from aqueous solutions by γ-Fe2 O 3–TiO 2 magnetic nanoparticles
Environ Sci Pollut Res through simultaneous photocatalytic oxidation and adsorption. J Hazard Mater 246–247:10–17 Yu X, Tong S, Ge M, Zuo J, Cao C, Song W (2013b) One-step synthesis of magnetic composites of cellulose@iron oxide nanoparticles for arsenic removal. J Mater Chem A 1:959–965 Yürüm A, Kocabaş-Ataklı ZÖ, Sezen M, Semiat R, Yürüm Y (2014) Fast deposition of porous iron oxide on activated carbon by microwave heating and arsenic (V) removal from water. Chem Eng J 242:321– 332
Zhang G, Ren Z, Zhang X, Chen J (2013) Nanostructured iron(III)copper(II) binary oxide: a novel adsorbent for enhanced arsenic removal from aqueous solutions. Water Res 47:4022–4031 Zhang M, Gao B (2013) Removal of arsenic, methylene blue, and phosphate by biochar/AlOOH nanocomposite. Chem Eng J 226:286–292 Zeng L (2003) A method for preparing silica-containing iron(III) oxide adsorbents for arsenic removal. Water Res 37:4351–4358 U.S. EPA (1992) 40 Codes of Regulations 261; U.S. Environmental Protection Agency: Washington, DC, Part 261, 31