J Mater Sci DOI 10.1007/s10853-015-9009-x

Preparation of nitrogen-functionalized mesoporous carbon and its application for removal of copper ions Zhiyun Li1,2 • Sili Ren1

Received: 10 February 2015 / Accepted: 3 April 2015 Ó Springer Science+Business Media New York 2015

Abstract Nitrogen-functionalized mesoporous carbon (NMC) materials with high nitrogen content were synthesized through a hard template method using ionic liquid of 1-cyanomethyl-3-methylimidazolium bromide as the precursor and LUDOX HS-40 colloidal silica as the template. The obtained NMCs were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption and desorption analysis, X-ray photoelectron spectroscopy, and elemental analysis. It was shown that the carbonization temperature played a critical role in determining the physiochemical properties and the nitrogen content of the carbon materials. The obtained nitrogen-functionalized mesoporous carbon carbonized at 800 °C possessed disordered mesoporous structure with very high specific surface area of 1028 m2 g-1, large pore volume of 0.94 cm3 g-1, and high nitrogen content of 21.0 wt%. The adsorption performance of the prepared NMCs was investigated by removing Cu2? from aqueous solutions and the adsorption capacity could attain 117.1 mg g-1 at an optimal condition. The kinetic and isothermal analysis revealed that the removal of Cu2? by the NMCs belongs to chemical monolayer adsorption, suggesting the strong interaction between Cu2? and the adsorbent. The XPS spectra of N1s before and after adsorption of Cu2? suggested that the pyridinic-type nitrogen was the dominant groups of the adsorbent in the adsorption process.

& Sili Ren [email protected] 1

State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, People’s Republic of China

2

University of Chinese Academy of Sciences, Beijing 100039, People’s Republic of China

Furthermore, the material was separated from solution by filtration and displayed a superior reusability in the recycling test.

Introduction Water is the source of all life. However, the serious water pollution from the heavy metal ions has threatened human health [1]. It is imperative to remove the heavy metal ions from the industrial effluents prior to disposal. Various techniques including chemical precipitation [2, 3], ion exchange [4, 5], membrane filtration [6, 7], and adsorption [8–11] have been developed for the removal of heavy metal ions from wastewater. Among these methods, adsorption is an attractive approach for its characteristics such as easy to handle, low cost, and highly efficient [12]. For this purpose, developing different kinds of effective adsorbents has attracted considerable attention. Mesoporous materials have been proved to be effective adsorbents due to their extremely high surface area and large porosity [13–16]. Mesoporous materials are widely used in many fields of science and technology, including catalysis [17, 18], separation [19–21], and energy storage/conversion [22, 23]. Heteroatom functionalization could profitably affect the physicochemical properties of the materials and then extend the range of application. For example, nitrogenfunctionalized mesoporous carbon could improve various performances such as the conductivity, basicity, oxidation stability, catalytic activity, and adsorption capacity. For the adsorption processes, N-containing functional groups could not only act as adsorption sites increasing the electrostatic interaction between the adsorbent and adsorbate, but also raise the hydrophilicity of the adsorbent to improve the adsorption capacity. However, the synthesis of NMCs is

123

J Mater Sci

often limited by the nitrogen-containing precursors. The most popular precursors are polyacrylonitrile (PAN) [24], polypyrrole (PPy) [25], polyaniline [26], poly(furfuryl alcohol) [27], and melamine [28]. However, these polymers and organic precursors are difficult to handle because organic compounds will completely evaporate or decompose to gaseous substance during high-temperature carbonization, while polymer precursors possess the drawbacks of low solubility, solid-state, and complex synthesis [29]. So the choice of a suitable nitrogen-rich carbon precursor is very important. Recently, ionic liquids (ILs) have been used as carbon precursors in the synthesis of carbon materials because of their thermal stabilities, intrinsic negligible vapor pressure, and the diversification of composition [30, 31]. Dai and coworkers successfully synthesized mesoporous carbon materials from nitrile-functionalized ionic liquids precursors [32]. The nitrogen-rich carbons exhibit high adsorption capacity for CO2 and selectivity for CO2/N2 separation. Antonietti and co-workers synthesized nitrogen-doped carbons from ionic liquids and poly(ionic liquid)s and the carbon materials were applied in a multitude of fields [31]. Recently, Chen et al. synthesized nitrogen-doped hollow tubular magnetically mesoporous carbon with SBA-15 as the template and the carbon was used as an absorbent for the removal of Cu2? [33]. It still needs much efforts on preparing nitrogen-functionalized mesoporous carbon as highly efficient copper adsorbent with large adsorption capacity. In this work, in order to improve the nitrogen content and surface area of materials, we report the synthesis method of nitrogen-functionalized mesoporous carbon using 1-cyanomethyl-3-methylimidazolium bromide as a precursor and LUDOX HS-40 as the hard template. The obtained materials exhibited highly efficient adsorption activity for the removal of Cu2? from the wastewater.

Experimental section Materials 1-Methylimidazole was purified by distilling prior to use. Bromoacetonitrile was analytical purity grade and used as received. Mesoporous silica template (LUDOX HS-40) was purchased from Sigma-Aldrich. Ultrapure water was used through the experiments. Synthesis of the nitrogen-functionalized mesoporous carbon materials The ion liquid precursor of 1-cyanoethyl-3-methylimidazolium bromide ([MCNIm]Br) was first synthesized. Under

123

vigorous stirring, bromoacetonitrile (8.7 g, 73 mmol) was added dropwise to 1-methylimdazole (5 g, 61 mmol) solution in methanol at room temperature. Stirring was continued for 12 h, and precipitate was formed in the solution mixture, which was filtered under reduced pressure. After being washed with diethyl ether and dried under vacuum, the desired precursor of [MCNIm]Br was obtained in a 96 % yield. The synthetic route for preparation of the nitrogenfunctionalized mesoporous carbon is shown in Scheme 1. The carbon materials were obtained by carbonizing a mixture of the precursor of [MCNIm]Br and mesoporous silica template (LUDOX HS-40). In detail, 22 g of the colloidal silica and 10 g of the IL precursor were added into a 250 mL of round-bottom flask with 150 mL deionized water. The resultant mixture was heated to 100 °C to volatilize the solvent under stirring. The residual solid mixture was ground into powder to obtain IL@silica intermediate. Then, the solid mixture of IL@silica and ZnCl2 (1:1) was transferred into a tube furnace for carbonization. The temperature was raised from room temperature to a final temperature (500, 600, 700, or 800 °C) at a controllable ramping rate of 10 °C min-1, and maintained for an hour under argon. After cooling to room temperature, the obtained carbon@silica intermediate was treated by a 10 % HF solution at 65 °C for 12 h. This procedure was repeated twice to remove the silica template completely. Finally, the resultant powder was washed with water and dried under vacuum at 80 °C. As a result, the nitrogen-functionalized mesoporous carbon was obtained and denoted as NMC-X (X = 500, 600, 700, 800), respectively.

Characterization of the NMC-X X-ray diffraction (XRD) analysis of the NMCs was performed on a Rigaku D/max-2400 diffractometer operating at 40 kV and 150 mA. The mesoporous nature of the NMC materials was characterized with a transmission electron microscopy (TEM, FEI Tecnai G2 TF20) operating at 200 kV. Specific surface areas of the NMC materials were determined by nitrogen adsorption and desorption isotherms (BET isotherms) at 77 K using a Micromeritics ASAP 2020 HD surface area & pore size analyzer. Prior to measurement, all the samples were degassed at 350 °C for 4 h. The specific surface areas of the NMC materials were calculated using Brunanuer-Emmet-Teller (BET) method, while the pore size distribution plots were obtained using Barrett–Joyner–Halenda (BJH) method. The nitrogen amount adsorbed at a relative pressure of P/P0 = 0.9989 was used to estimate the total pore volume. X-ray photoelectron spectroscopy (XPS) characterization was conducted on a Thermo Fisher Scientific ESCALAB 25Xi

J Mater Sci Scheme 1 Schematic diagram of the preparation of NMCs

N

N

CN

LUDOX HS-40

Br IL

SiO2

1. Carbonization 2. Template Removal

IL@SiO2

NMC

spectrometer. Elemental analysis (EA) was performed on a Vario EL elemental analyzer. Copper adsorption The copper adsorption tests were carried out in the shaking table at 160 rpm and 30 ± 1 °C using 100 mL flasks containing the Cu2? solutions with different initial concentration. The effects of temperature, pH value, contact time, and adsorption isotherms were investigated. The pH values of the solutions were adjusted by 0.1 mol L-1 HCl or NaOH solutions. After adsorption, the mixture was separated by centrifugation and the concentration of the residual Cu2? in the solution was measured by flame atomic absorption spectrometry (Varian AA240). The adsorption capacity qe (mg g-1) was calculated according to the following equation: ðC0  Ce Þ V; qe ¼ m

Fig. 1 XRD patterns of NMC-X

ð1Þ

where C0 (mg L-1) and Ce (mg L-1) are the initial and equilibrium concentration of Cu2?, respectively, V (L) is the volume of the solution, and m (g) is the mass of the adsorbent.

Results and discussion Characterization of the NMC-X The XRD patterns of the NMC-X were characterized and the results are shown in Fig. 1. Peaks at about 22.5° and 40.7° were assigned to the (002) and (100) planes of the graphite crystal, respectively, indicating the graphitic structure of the materials. The TEM images of the NMCs are shown in Fig. 2. It was observed that the materials possessed highly disordered interconnected mesoporous network. The size of these pores resulted from the monodispersed colloidal silica particles was relatively uniform. Under low carbonization temperature, only small size of pores was observed. The mesoporous characteristics were analyzed by N2 adsorption–desorption isotherms shown in Fig. 3a. The NMC-700 and NMC-800 displayed representative type-IV curves with H1/H3-type hysteresis loop at a wide P/P0 range from 0.4 to 1.0, indicating the

existence of mesoporous structure [34]. However, the isotherms of NMC-500 and NMC-600 were assigned to typeIV curves with a pronounced H4-type hysteresis loop. The pore size distributions derived from the desorption branch of isotherms using BJH method showed that the pores on NMCs usually possess two sizes. For example, the pore sizes for NMC-800 are centered at about 3.5 and 9.4 nm, respectively (Fig. 3b). However, for NMC-500 and NMC600, mainly small size of pores was obtained centered at about 3.5 nm, which was consistent with the observed TEM images. The BET surface area and pore volume of the NMCs are shown in Table 1. It confirmed that carbonization temperature clearly affected pore architecture. Below 600 °C, pore structures are apparently not developed. The BET surface area and pore volume of NMC-500 are 10 m2 g-1 and 0.03 cm3 g-1, respectively. However, they increased sharply up to 1028 m2 g-1 and 0.94 cm3 g-1 when the carbonization temperature reached 800 °C. Compared with other N-functionalized mesoporous carbon materials using ionic liquids as precursors but different templates such as SBA-15 [35] or by the method of direct carbonization [29], the BET surface area and pore volume are relatively high. Elemental analysis revealed that the nitrogen content of the NMC-X (X = 500, 600, 700, 800) materials was as high as 19.4, 25.2, 23.1, and 21.0 wt%, respectively. The nitrogen

123

J Mater Sci

Fig. 3 The N2 adsorption/desorption isotherms (a) and BJH pore size distributions (b) of NMC-X

[26], and melamine [28], which indicating a high adsorption capacity. The XPS spectra of the NMCs showed strong signals from carbon, nitrogen, and oxygen elements. Especially, the N1s peak of NMCs could be well fitted to two peaks (Fig. 4), in which the lower energy peak near 398.4 eV was assigned to pyridinic-type nitrogen and the peak centered at about 400.2 eV was attributed to pyrrolictype nitrogen [36]. The quantitative analysis of XPS revealed that the nitrogen content on the surface of NMCs was well consistent with the corresponding EA results, which is shown in Table 1. Such result indicates that the nitrogen elements are distributed homogeneously in the framework of NMCs. Fig. 2 The TEM images of NMC-600 (a), NMC-700 (b), and NMC800 (c)

content was much higher than mesoporous carbon materials obtained by carbonizing other nitrogen-rich precursors such as polyacrylonitrile [24], polypyrrole [25], polyaniline

123

Effect of solution pH on the Cu21 adsorption by NMC-800 The removal of Cu2? from aqueous solution by adsorption is highly dependent on the pH of the solution, which considerably affects the surface charge of the adsorbent

J Mater Sci Table 1 The pore characteristics and nitrogen content of NMC-X Sample

Surface area (m2 g-1)

Pore volume (cm3 g-1)

Nitrogen content (wt%)

Surface nitrogen content (at.%)

NMC-800

1028

0.94

21.0

19.3

NMC-700

1018

0.87

23.1

17.6

NMC-600

532

0.37

25.2

19.4

NMC-500

10

0.03

19.4

25.3

and the copper speciation [37]. As shown in Fig. 5, the Cu2? removal efficiency of the NMC-800 was poor when the pH value was very low such as less than 2. Such result was attributed to the fact that the nitrogen element in the carbon materials could be easily protonated at a low pH solution, leading to an electrostatic repulsion of the carbon material with the Cu2?. With the increase in solution pH from 1.4 to 4.0, the protonation of the nitrogen atoms would be decreased, resulting in a reduction of the electrostatic repulsive force and an increase of the adsorption capacity of the adsorbents. However, as the solution pH increased from 4.0 to 6.0, the adsorption capacity of the NMC-800 had no obvious variation, indicating that the adsorption sites on the surface of the adsorbent had been fully taken up by Cu2? [38]. When the pH value was further increased over 6.0, the adsorption capacity had a sharp increase, which was attributed to the formation of metalhydroxide and did not represent a true adsorption capacity of the NMC-800.

As shown in Fig. 6b, the pseudo-second order is more suitable for depicting the adsorption kinetics, suggesting that the adsorption process might be controlled by chemical adsorption involving valence forces through sharing or exchanging electrons between adsorbent and adsorbate [39, 40].

Kinetic study of copper removal

qe ¼

Investigation on the adsorption kinetics is essential to evaluate the performance of the adsorbent and gain insight into the underlying mechanisms. The time dependence of Cu2? adsorption by the NMC-800 was studied at pH 5.6 with initial Cu2? concentration of 50 ppm. As shown in Fig. 6a, the adsorption rate was relatively fast within 60 min and then slowed down till the adsorption reached an equilibrium state after 360 min. To have a deep understanding on the adsorption kinetics, pseudo-first-order and pseudo-second-order kinetic models were employed to fit the experimental data, respectively. The equations are described as follows:

qe ¼ Kf Ce1=n ;

lnðqe  qt Þ ¼ ln qe  k1 t

ð2Þ

t 1 t ¼ þ ; qt k2 q2e qe

ð3Þ

where qt and qe (mg g-1) are the amount of metal ions adsorbed on the material at time t (min) and at equilibrium, respectively, and k1 (min-1) and k2 (mg g-1 min-1) are the pseudo-first-order and pseudo-second-order rate constants.

Adsorption isotherm The equilibrium adsorption isotherm provides useful information on the capacity of the adsorbent, surface properties, and the affinity between the adsorbent and adsorbate, which helps to improve the adsorption system [12]. The Cu2? adsorption isotherm was obtained via stepwise variation of the initial Cu2? concentration from 5 to 100 ppm at 30 °C and pH 5.6. As shown in Fig. 7, Langmuir [41] and Freundlich [42] adsorption isotherms were used to describe the adsorption process. The equations are described as follows: Qmax bCe 1 þ bCe

ð4Þ ð5Þ

where qe (mg g-1) is the equilibrium adsorption capacity, Ce (mg L-1) is the equilibrium concentration of ions in solution, Qmax (mg g-1) is the maximum adsorption capacity per gram of adsorbent, b (L mg-1) is the Langmuir constant related to the energy of adsorption, Kf (mg g-1), and n are the Freundlich constants related to adsorption capacity and heterogeneity factor, respectively. Comparing the correlation coefficients, it was shown that the Langmuir isotherm (R2 [ 0.99) could better describe the adsorption process (Fig. 7b), implying that a chemical monolayer adsorption occurred between the Cu2? and the adsorbent of NMC-800 [43]. The maximum adsorption capacity (Qmax) for NMCs adsorbing the Cu2? derived from the Langmuir model is 117.1 mg g-1. A comparison between the sorption capacity of the synthetic NMC-800 and reported literature is summarized in Table 2. Compared with the reported adsorbents, the NMC-800 possesses much higher adsorption capacity for Cu2? due to the high nitrogen content, large BET surface area, and pore volumes.

123

J Mater Sci

Fig. 5 Effect of the solution pH on Cu2? adsorption capacity by NMC-800

Effect of temperature on the Cu21 adsorption by NMC-800 Temperature is also an important factor to affect the performance of the adsorbent. Effect of temperature on the adsorption capacity of NMC-800 was investigated by placing 10 mg adsorbent in 25 mL solution of 50 mg L-1 Cu2? shaking at 160 rpm for 12 h. As shown in Fig. 8, the Cu2? removal efficiency increased when the temperature was raised from 20 to 40 °C. However, with the further increase in temperature, the adsorption capacity dramatically reduced. This might attribute to the fact that Cu2? have an increasing tendency to escape from the solid surface to the bulk solution with the temperature rising [48]. Obviously, 40 °C is an optimal temperature for the adsorption of Cu2? with the NMC-800. The Cu21 adsorption capacity of NMC-X and possible adsorption mechanism

Fig. 4 XPS high-resolution spectra for N1s of various samples: a NMC-500, b NMC-600, c NMC-700, and d NMC-800

123

As shown in Table 3, with the increase in carbonization temperature, the adsorption capacity of NMC-X for Cu2? becomes gradually smaller, which is corresponding with the change of the content of pyridinic-type nitrogen. It is possible that the removal of Cu2? is associated with pyridinic-type nitrogen. To further investigate the adsorption mechanism, XPS spectra of NMC-800 before and after Cu2? adsorption were conducted. As shown in Fig. 9, the two peaks at binding energies of 398.4 and 400.2 eV were assigned to pyridinic-type and pyrrolic-type nitrogen, respectively. After Cu2? adsorption, the peak at 398.4 eV was shifted to 398.6 eV, which indicates that the Cu2? adsorption process took place on the pyridinic-type

J Mater Sci

Fig. 6 Kinetic study of Cu2? adsorption by NMC-800: a the adsorption amount as a function of time, b, c linear fitting by the pseudo-first-order and the pseudo-second-order model

Fig. 7 a Adsorption isotherm plot, b, c linear fitting of the equilibrium data using Langmuir and Freundlich model

123

J Mater Sci Table 2 Comparison of Cu2? sorption capacity from the literature by various adsorbents

Sorption capacity (mg g-1)

Adsorbent

Reference

Chitosan–tripolyphosphate beads

26.06

[8]

Natural bentonite

44.48

[44] [45]

Biosorbents

87.05

Hydrolyzed polyacrylonitrile fiber

29.64

[38]

Polymeric adsorbent

74.29

[46]

Functionalized SBA-16 Functionalized mesoporous adsorbent N-doped ordered mesoporous carbon-Fe Nitrogen-functionalized mesoporous carbon

36.38

[47]

145.98

[16]

23.6

[33]

117.1

This study

The co-existing cations may have effects on the sorption capacity. To investigate the selectivity of the NMCs, multimixture metal ions (Na?, Ca2?, Mg2?, Pb2?, Ni2?, and Zn2?) were added equally to the Cu2? solution, and the sorption efficiency of NMC-800 is shown in Fig. 10. The Cu2? gave the best sorption efficiency up to 97 % and the

Pb2? followed with 65 %, indicating that the NMC-800 possessed high removal efficiency even in the existing competing metal ions. To evaluate desorption and regeneration of the NMCs, the NMC-800 after adsorption of Cu2? was eluted with 2 mol L-1 HCl elution twice, and then applied to adsorption. Figure 11 indicates that the adsorption capacity of NMC-800 for Cu2? was still high after 5 cycles (86 % of initial adsorption capacity) although the removal efficiency declined with the cycles. This demonstrates that the NMC materials could be regenerated effectively and thus be used repeatedly. Therefore, the synthetic NMC materials may be the potential adsorbent for removal of Cu2? from polluted environmental effluents.

Fig. 8 Effect of temperature on Cu2? adsorption capacity by NMC800

Fig. 9 XPS spectra of N1s for NMC-800 before and after Cu2? adsorption

nitrogen [49]. As a result, the electrostatic interaction between Cu2? and pyridinic-type nitrogen is the possible mechanism. Effect of competing ions and regeneration of the adsorbent

Table 3 Quantitative analysis of the two types of nitrogen from the XPS spectra and adsorption capacity of NMC-X

123

Sample

Pyridinic N (wt%)

Pyrrolic N (wt%)

Adsorption capacity (mg g-1)

NMC-500

48.0

52.0

84.13

NMC-600

39.5

60.5

82.70

NMC-700

36.3

63.7

80.75

NMC-800

30.0

70.0

68.34

J Mater Sci

adsorbent. The XPS spectra of N1s before and after adsorption of Cu2? suggested that the pyridinic-type nitrogen was the dominant groups of the adsorbent in the adsorption process. Moreover, the material was separated from solution by filtration and displayed a superior reusability in the recycling test. Acknowledgements The authors acknowledge the financial support from the National Natural Science Foundation of China (Grant 51374195) and the ‘‘100 Talents Program’’ held by the Chinese Academy of Science (CAS).

References Fig. 10 Competitive Cu2? removal by NMC-800 in the presence of multi-metal ions

Fig. 11 Recycling test of Cu2? adsorption on NMC-800

Conclusion The NMCs with high nitrogen content were successfully synthesized through a hard template method using ionic liquid of 1-cyanomethyl-3-methylimidazolium bromide as the precursor and LUDOX HS-40 colloidal silica as the template. Carbonization temperature determined the physiochemical properties such as BET surface area, pore volume, and nitrogen content of the carbon materials. The obtained material of NMC-800 possessed disordered mesoporous structure with very high specific surface area, large pore volume, and high nitrogen content and presented excellent adsorption capacity for removal of Cu2? up to 117.1 mg g-1 at an optimal condition. The kinetic and isothermal analysis revealed that the removal of Cu2? by the NMCs belongs to chemical monolayer adsorption, suggesting the strong interaction between Cu2? and the

1. Hill MK (2010) Understanding environmental pollution. Cambridge University Press, Cambridge 2. Matlock MM, Howerton BS, Atwood DA (2002) Chemical precipitation of lead from lead battery recycling plant wastewater. Ind Eng Chem Res 41(6):1579–1582 3. Matlock MM, Howerton BS, Atwood DA (2002) Chemical precipitation of heavy metals from acid mine drainage. Water Res 36(19):4757–4764 4. Verbych S, Hilal N, Sorokin G, Leaper M (2005) Ion exchange extraction of heavy metal ions from wastewater. Separ Sci Technol 39(9):2031–2040 5. Dabrowski A, Hubicki Z, Podkos´cielny P, Robens E (2004) Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 56(2):91–106 6. Zeng G-M, Xu K, Huang J-H, Li X, Fang Y-Y, Qu Y-H (2008) Micellar enhanced ultrafiltration of phenol in synthetic wastewater using polysulfone spiral membrane. J Membr Sci 310(1):149–160 7. Borbe´ly G, Nagy E (2009) Removal of zinc and nickel ions by complexation–membrane filtration process from industrial wastewater. Desalination 240(1):218–226 8. Ngah W, Fatinathan S (2010) Adsorption characterization of Pb(II) and Cu (II) ions onto chitosan-tripolyphosphate beads: kinetic, equilibrium and thermodynamic studies. J Environ Manage 91(4):958–969 9. Wen Y, Ma J, Chen J, Shen C, Li H, Liu W (2015) Carbonaceous sulfur-containing chitosan–Fe(III): a novel adsorbent for efficient removal of copper (II) from water. Chem Eng J 259:372–380 10. Tian H, Feng Q, Chen Y, Yang H, Li X, Lu P (2015) Synthesis of amino-functionalized mesoporous materials with environmentally friendly surfactants by evaporation-induced self-assembly and their application to the adsorption of lead(II) ions. J Mater Sci 50(7):2768–2778. doi:10.1007/s10853-015-8832-4 11. Awual MR, Hasan MM (2015) Colorimetric detection and removal of copper(II) ions from wastewater samples using tailormade composite adsorbent. Sens Actuat B 206:692–700 12. Rajurkar NS, Gokarn AN, Dimya K (2011) Adsorption of chromium (III), nickel (II), and copper (II) from aqueous solution by activated alumina. CLEAN–Soil, Air Water 39(8):767–773 13. Wu Z, Li W, Webley PA, Zhao D (2012) General and controllable synthesis of novel mesoporous magnetic iron oxide@carbon encapsulates for efficient arsenic removal. Adv Mater 24(4):485– 491 14. Wang X, Pei Y, Lu M, Lu X, Du X (2015) Highly efficient adsorption of heavy metals from wastewaters by graphene oxideordered mesoporous silica materials. J Mater Sci 50(5):2113– 2121. doi:10.1007/s10853-014-8773-3

123

J Mater Sci 15. Wu Z, Zhao D (2011) Ordered mesoporous materials as adsorbents. Chem Commun 47(12):3332–3338 16. Awual MR, Yaita T, El-Safty SA, Shiwaku H, Suzuki S, Okamoto Y (2013) Copper(II) ions capturing from water using ligand modified a new type mesoporous adsorbent. Chem Eng J 221:322–330 17. Li Z, Liu J, Xia C, Li F (2013) Nitrogen-functionalized ordered mesoporous carbons as multifunctional supports of ultrasmall pd nanoparticles for hydrogenation of phenol. ACS Catalysis 3(11):2440–2448 18. Goettmann F, Fischer A, Antonietti M, Thomas A (2006) Chemical synthesis of mesoporous carbon nitrides using hard templates and their use as a metal-free catalyst for friedel-crafts reaction of benzene. Angew Chem Int Ed 45(27):4467–4471 19. Awual MR (2015) A novel facial composite adsorbent for enhanced copper(II) detection and removal from wastewater. Chem Eng J 266:368–375 20. Awual MR, Yaita T, Okamoto Y (2014) A novel ligand based dual conjugate adsorbent for cobalt(II) and copper(II) ions capturing from water. Sens Actuat B 203:71–80 21. Awual MR, Ismael M, Yaita T, El-Safty SA, Shiwaku H, Okamoto Y, Suzuki S (2013) Trace copper(II) ions detection and removal from water using novel ligand modified composite adsorbent. Chem Eng J 222:67–76 22. Wang J, Xin HL, Wang D (2014) Recent progress on mesoporous carbon materials for advanced energy conversion and storage. Part Part Syst Char 31(5):515–539 23. Li Q, Jiang R, Dou Y, Wu Z, Huang T, Feng D, Yang J, Yu A, Zhao D (2011) Synthesis of mesoporous carbon spheres with a hierarchical pore structure for the electrochemical double-layer capacitor. Carbon 49(4):1248–1257 24. Lu A, Kiefer A, Schmidt W, Schu¨th F (2004) Synthesis of polyacrylonitrile-based ordered mesoporous carbon with tunable pore structures. Chem Mater 16(1):100–103 25. Fuertes AB, Centeno TA (2005) Mesoporous carbons with graphitic structures fabricated by using porous silica materials as templates and iron-impregnated polypyrrole as precursor. J Mater Chem 15(10):1079–1083 26. Vinu A, Anandan S, Anand C, Srinivasu P, Ariga K, Mori T (2008) Fabrication of partially graphitic three-dimensional nitrogen-doped mesoporous carbon using polyaniline nanocomposite through nanotemplating method. Micropor Mesopor Mat 109(1–3):398–404 27. Park I-S, Choi M, Kim T-W, Ryoo R (2006) Synthesis of magnetically separable ordered mesoporous carbons using furfuryl alcohol and cobalt nitrate in a silica template. J Mater Chem 16(33):3409–3416 28. Chen H, Sun F, Wang J, Li W, Qiao W, Ling L, Long D (2013) Nitrogen Doping Effects on the Physical and Chemical Properties of Mesoporous Carbons. J Phys Chem C 117(16):8318–8328 29. Zhang S, Dokko K, Watanabe M (2014) Direct synthesis of nitrogen-doped carbon materials from protic ionic liquids and protic salts: structural and physicochemical correlations between precursor and carbon. Chem Mater 26(9):2915–2926 30. Lee JS, Wang X, Luo H, Baker GA, Dai S (2009) Facile ionothermal synthesis of microporous and mesoporous carbons from task specific ionic liquids. J Am Chem Soc 131(13): 4596–4597 31. Yuan J, Giordano C, Antonietti M (2010) Ionic liquid monomers and polymers as precursors of highly conductive, mesoporous, graphitic carbon nanostructures. Chem Mater 22(17):5003–5012

123

32. Fulvio PF, Lee JS, Mayes RT, Wang X, Mahurin SM, Dai S (2011) Boron and nitrogen-rich carbons from ionic liquid precursors with tailorable surface properties. Phys Chem Chem Phys 13(30):13486–13491 33. Chen A, Yu Y, Zhang Y, Xing T, Wang Y, Zhang Y, Zhang J (2014) Solid–solid grinding/templating route to magnetically separable nitrogen-doped mesoporous carbon for the removal of Cu2? ions. J Hazard Mater 279:280–288 34. Kruk M, Jaroniec M (2001) Gas adsorption characterization of ordered organic-inorganic nanocomposite materials. Chem Mater 13(10):3169–3183 35. Paraknowitsch JP, Zhang J, Su D, Thomas A, Antonietti M (2010) Ionic liquids as precursors for nitrogen-doped graphitic carbon. Adv Mater 22(1):87–92 36. Biniak S, Szyman´ski G, Siedlewski J, S´wiatkowski A (1997) The characterization of activated carbons with oxygen and nitrogen surface groups. Carbon 35(12):1799–1810 37. Madhava Rao M, Ramesh A, Purna Chandra Rao G, Seshaiah K (2006) Removal of copper and cadmium from the aqueous solutions by activated carbon derived from Ceiba pentandra hulls. J Hazard Mater 129(1–3):123–129 38. Deng S, Bai R, Chen JP (2003) Behaviors and mechanisms of copper adsorption on hydrolyzed polyacrylonitrile fibers. J Colloid Interf Sci 260(2):265–272 39. Ho YS, McKay G (1999) Pseudo-second order model for sorption processes. Process Biochem 34(5):451–465 40. Huang Y, Li S, Chen J, Zhang X, Chen Y (2014) Adsorption of Pb(II) on mesoporous activated carbons fabricated from water hyacinth using H3PO4 activation: adsorption capacity, kinetic and isotherm studies. Appl Surf Sci 293:160–168 41. Langmuir I (1918) The adsorption of gases on plane surfaces of glass, mica and platinum. J Am Chem Soc 40(9):1361–1403 ¨ ber die adsorption in lo¨sungen. Zeitschrift 42. Freundlich H (1906) U fu¨r Physikalische 43. Gu¨nay A, Arslankaya E, Tosun ˙I (2007) Lead removal from aqueous solution by natural and pretreated clinoptilolite: adsorption equilibrium and kinetics. J Hazard Mater 146(1–2):362– 371 44. Veli S, Alyu¨z B (2007) Adsorption of copper and zinc from aqueous solutions by using natural clay. J Hazard Mater 149(1):226–233 45. Mohan D, Pittman CU Jr, Steele PH (2006) Single, binary and multi-component adsorption of copper and cadmium from aqueous solutions on Kraft lignin—a biosorbent. J Colloid Interf Sci 297(2):489–504 46. Liu C, Bai R, San Ly Q (2008) Selective removal of copper and lead ions by diethylenetriamine-functionalized adsorbent: behaviors and mechanisms. Water Res 42(6–7):1511–1522 47. Xue X, Li F (2008) Removal of Cu(II) from aqueous solution by adsorption onto functionalized SBA-16 mesoporous silica. Micropor Mesopor Mat 116(1–3):116–122 48. Kula I, Ug˘urlu M, Karaog˘lu H, C¸elik A (2008) Adsorption of Cd(II) ions from aqueous solutions using activated carbon prepared from olive stone by ZnCl2 activation. Bioresource Technol 99(3):492–501 49. Chen H, Yan T, Jiang F (2014) Adsorption of Cr(VI) from aqueous solution on mesoporous carbon nitride. J Taiwan Inst Chem E 45(4):1842–1849