Monatshefte für Chemie - Chemical Monthly https://doi.org/10.1007/s00706-018-2168-0 (0123456789().,-volV)(0123456789().,-volV)

ORIGINAL PAPER

b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its application for adsorption of organic dye Yunlong Wu1 • Zerun Zhao1 • Mingliang Chen1 • Zefeng Jing1 • Fengxian Qiu1 Received: 1 December 2016 / Accepted: 2 February 2018  Springer-Verlag GmbH Austria, part of Springer Nature 2018

Abstract In this work, a novel b-cyclodextrin–graphene oxide–diatomaceous earth material (b-CD-GO-DE) was prepared and its application as excellent adsorbent was carried out for adsorption of methylene blue in aqueous solution. The structure and morphology of b-CD-GO-DE material were evidenced using Fourier-transform-infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometer, and thermogravimetric analysis. The adsorption experiment for removal of methylene blue was investigated in detail. The highest adsorption efficiency can reach 98.5% at 0.02 g cm-3 dosage of b-CD-GO-DE, the temperature of 65 C, and time of 3 h. Adsorption kinetics and adsorption isotherm were investigated. Pseudo-second-order kinetics model can describe the adsorption process appropriately. The adsorption isotherm data were simulated using Langmuir and Freundlich isotherm models and the results showed that the equilibrium data were fitted well with Langmuir isotherm model, the maximum adsorption capacity of methylene blue reached 110.50 mg g-1. The adsorbent has good regeneration performance. The proposed method shows that the b-CDGO-DE could be applied to adsorb of methylene blue in wastewater with satisfactory result. Graphical abstract

Keywords Graphene oxide  b-Cyclodextrin  Diatomaceous earth  Adsorption  Methylene blue

Introduction Due to rapid textile industrial development, pollution of printing and dyeing wastewater is an issue of major concern. The presence of dyes in the wastewater which are & Fengxian Qiu [email protected] 1

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China

complex organic compounds containing azo bond and aromatic nucleus, even the low concentrations, is deleterious to human beings and microorganisms, influence the water self-purification, and reduce the light transmittance [1, 2]. Therefore, the governance of dyeing wastewater has great significance. At present, various technologies were developed for treatment of dye contaminants from wastewater, including physical method, chemical method, and biological method [3, 4]. However, adsorption method received a great deal of attention for removal of dye from

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wastewater own to effectiveness, economy, and simple operation. Various materials have been devoted into the researches of adsorption, including activated carbon [5], bentonite [6], sawdust [7], flyash [8], and so on. Methylene blue (MB) is an organic dye and widely used in many fields, including paper, food processing, plastics, and printing (Fig. 1). The toxicity of MB is not strong, but still has certain influence to health of human. In addition, it is known that strong adsorption ability on the solid surface, MB, often regarded as a model for removing dyes and organic pollution from solutions [9]. Recently, graphene received extensive attention due to its excellent physical and chemical properties and potential application value. The two-dimensional structure of graphene composed of carbon atoms in sp2 hybridization [10, 11], and this hybrid model made carbon atoms and the adjacent three carbon atoms form stable C–C bonds through r bond. On the perpendicular to the plane of the graphene, a large number of carbon atoms provide p electron, in which electrons can move freely, so the graphene usually has excellent electrical conductivity, high mechanical strength, and thermal performance [12, 13]. Graphene oxide (GO) is one of the important derivatives of graphene, and the structure of GO is approximately the same as the graphene which contains abundant oxygen functional groups, such as hydroxyl, carbonyl, and carboxyl groups, both on the basal planes and at the edges of GO sheets [14]. These functional groups are essential for adsorption and make GO can be better dispersed in water. In addition, the chemical functionalization of GO can disperse in variety of organic solvents stably to form GO suspension. It can be known that GO shows high adsorption performance, large surface area, and chemical stability [15]. Furthermore, GO with other chemically adsorbents will reduce the accumulation of GO and increase adsorption capacity of the composite material. b-Cyclodextrin (b-CD) is a cyclic oligosaccharide containing seven D-(?)-glucopyranose units connected by a1,4-glucose linkages with a hydrophobic inner cavity and a hydrophilic exterior [16, 17]. Due to the hydrophobic cavity structure, b-CD has capability to forming stable host–guest inclusion with various compounds such as dyes, heavy metal ions, and small organic and inorganic molecules by virtue of a series of weak intermolecular

forces [18]. The cavity of b-CD has certain rigidity, because the hydroxyl at the edge of cavity formed hydrogen bond. In addition, b-CD is also environmental friendly; it can improve the solubility and stability of composite materials [19] and could be attached on the surface of GO sheets by hydrogen bonds, so it can improve the adsorption capacity of materials. Diatomaceous earth (DE) or diatomite is naturally debris of diatoms, which growth in ocean or lake, in the bottom sediment. It typically consists of 87–91% silicon dioxide (SiO2), with significant quantities of (Al2O3) and ferric oxide (Fe2O3) [20]. Due to its specific properties, such as porous structure, low density, fine particle size, high melting point, and chemical stability, DE, often used in industrial production as filtration media [21]. These properties illustrate that DE is a potential adsorbent for removal pollutants found in industrial wastewater including dyes and expected to become the low-cost adsorbent instead of activated carbon [22]. Different from other adsorbents, the unique structure of DE surface has hydroxyl groups which make it present weak acid in aqueous solution. Usually, the particle surface of DE with a negative charge, it is advantage for adsorption of metal ion adsorption, cationic dyes, and polymers. In this work, a novel composite material (b-CD-GO-DE) was synthesized and used as adsorbents for removal of MB. Then, the structure and morphology of composite material were characterized by Fourier-transform-infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometer (XRD), and thermogravimetric analysis (TG). The influences of adsorption experiment such as the dosage of b-CD-GO-DE, temperature, and contact time were determined. The experimental equilibrium data were fitted to Langmuir and Freundlich adsorption models. In addition, the kinetic studied were also carried out to determine the characters of adsorption process. The reusability and regeneration experiment were also investigated. The results show that b-CD-GO-DE had excellent adsorption capacity and had good regeneration performance.

Results and discussion FT-IR characterization

Fig. 1 Structure of methylene blue (MB)

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FT-IR spectra of GO (a), b-CD (b), DE (c), and b-CD-GODE (d) are shown in Fig. 2. As can be seen from Fig. 2a, the peak located at 3409 cm-1 is strong stretching vibration adsorption peak of –OH. The characteristic adsorption peak at 1714 cm-1 is carbonyl (–C=O) stretching vibrations of the –COOH groups. The absorbance peak at 1628 cm-1 is attributed to graphite domain frame vibration

b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its…

Fig. 2 FT-IR spectra of GO (a), b-CD (b), DE (c), and b-CD-GO-DE (d)

which was not been oxidation of sp2 hybridization. Moreover, the peaks at 1056, 1382 cm-1 are C–O–C-stretching vibration of epoxy group and stretching vibration of hydroxyl, respectively. The above results illustrate that GO have been successfully prepared and a lot of the carboxyl, hydroxyl, and epoxy groups were contained in GO. From Fig. 2b, a strong stretching vibration adsorption peak of hydroxyl appears at 3430 cm-1, the stretching vibration peak of –CH2– appears at 2930 cm-1, the characteristic adsorption peak of C–O–C at 1034 cm-1, and the characteristic adsorption peak of a-1,4-glucose bonds in b-CD appears at 933 cm-1. All of these are characteristic peaks of b-CD. From Fig. 2c, the peak at 1085 cm-1 should be due to Si–O–Si in-plane vibration. Similar observations can be seen at 788 cm-1, which is also characteristic of silica. The weak adsorption peak at 614 cm-1 was attributed to Si–O deformation and Al–O stretching. As can be seen from Fig. 2d, the peak of stretching vibration of hydroxyl appeared 3409 cm-1 became broad, and it proved that the oxygen containing functional groups of GO has been reacted with the hydroxyl of b-CD formed a large number of hydrogen bonds. A stretching vibration peak of –CH2– in b-CD appeared at 2924 cm-1, and it explained that the skeleton of b-CD was not been damaged. In addition, the characteristic peak of silica also appeared at 788 cm-1, and it suggested that the DE was keep completely. From the above results, it can conclude that b-CD-GO-DE has been synthesized.

SEM and TEM analyses SEM images of GO (a), DE (b), b-CD-GO-DE (c), and TEM image of b-CD-GO-DE (d) are shown in Fig. 3. From

Fig. 3a, it can be seen clearly that the layer structure of GO, which has smooth surface and wrinkled edge. This layer structure is conducive to adsorption of dye later. From Fig. 3b, it is observed that disc-shaped structure of DE with highly developed macroporous. As can be seen from Fig. 3c, the GO wrapped on the surface of DE and block b-CD adhered on the surface of DE. The DE provided high porosity and permeability. The structure of DE still maintained, which provided a good possibility for dyes to be trapped and adsorbed. From TEM image of b-CD-GO-DE, it can also be seen clearly that the macroporous structure of DE and the thin layer of GO covered the surface of DE. From Fig. 3d, the cavity of bCD and layer of GO and DE are clearly observed. This phenomenon illustrates that the final composite materials, b-CD-GO-DE, have been synthesized and have large contact area, which are good possibility of dyes being adsorbed on its surface later.

XRD analysis XRD patterns of GO (a) and DE (b), b-CD-GO-DE (c), and b-CD (d) are shown in Fig. 4. As can be seen from Fig. 4a, a very sharp surface diffraction peak appears at 2h = 10.5 which is the characteristic diffraction peak of GO and the inter-layer spacing in the GO is 0.84 nm. This indicates that GO has crystallization and orderly structure. From Fig. 4b, it can be seen that the characteristic diffraction peak of DE appears at 2h = 21.8 with hole spacing of 0.407 nm. As can be seen from Fig. 4c, the composite material has the characteristic diffraction peaks of GO and DE at 2h = 10.5 and 21.8. From the XRD result of bCD-GO-DE, the diffraction peak characteristic of b-CD at 12.6 and 13.3 disappeared and shifted to 14.9, this is mainly because b-CD reacted with GO, and hydrogen bonds were formed between GO and b-CD, simultaneously. The results show that the b-CD-GO-DE has been synthesized.

TG analysis To examine the thermal stability of b-CD-GO-DE, TG analysis was performed. TG curve of b-CD-GO-DE is shown in Fig. 5. As can be seen from Fig. 5, the TG curve of b-CD-GO-DE has two weightlessness ladders (at T \ 150 C and 150–450 C, respectively). The first mass loss of 5.63% in the range of 50–150 C is attributed to the residual water. The second weight loss of 32.53% at 150–450 C might be attributed to the loss part of the hydroxyl (–OH) and carboxyl (–COOH) in GO, removal of weakly bonded between b-CD-GO and GE, and decompositions of b-CD and DE. According to the TG analysis, b-CD-GO-DE has better thermal stability; it is mainly

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Fig. 3 SEM images of GO (a), DE (b), b-CD-GO-DE (c), and TEM image of b-CD-GO-DE (d)

Fig. 4 XRD patterns of GO (a), DE (b), b-CD-GO-DE (c), and b-CD (d)

attributed to the molecular had large contact and produced interaction force easily.

Dye adsorption and mechanism To obtain the maximum adsorption quantity of MB by bCD-GO-DE, the dye adsorption experiment was performed to determine the best adsorption conditions. The effects of several parameters on the adsorption capacity of MB dye solution were investigated. The standard curve (kmax = 664 nm) of MB was obtained with the

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Fig. 5 TG curve of b-CD-GO-DE

concentration of MB range from 1 mg dm-3 to 10 mg dm-3 at temperature 25 C through visible spectrophotometer. The linear regression equation is y = 0.0928 ? 0.1767x, AND correlation coefficient R2 is 0.9959. In general, adsorption can be divided into two types, physical adsorption and chemical adsorption. In the physical adsorption, the force between adsorbate and the surface of adsorbent is intermolecular forces, which also named van der Waals force. While in the chemical adsorption, the valence bond force, which belongs to chemical bond,

b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its…

formed adsorption bonds between adsorbate and adsorbent. In addition, the same adsorption system may contain both physical adsorption and chemical adsorption; the adsorption type may also change with the change of the temperature. The adsorption process of adsorbed MB on b-CDGO-DE contained both physical adsorption and chemical adsorption. The surface of b-CD-GO-DE contains numerous of carboxyl and hydroxyl groups, which occurred ion exchange with MB dye molecules to form hydrogen bond. The adsorption mechanism of b-CD-GO-DE is shown in Fig. 6. The reaction route is shown in Route 1. Moreover, the b-CD-GO-DE material contains a large number of cavities of b-CD, and these cavities can parcel MB molecular to form host–guest inclusion compound. The process of adsorption is shown in Route 2.

Effect of the dosage of b-CD-GO-DE on the adsorption efficiency of MB solution Fixed at temperature of 25 C, adsorption time of 6 h, and 100 mg dm-3 of MB solution, effect of the dosage of bCD-GO-DE on the adsorption efficiency of MB solution is shown in Fig. 7. From Fig. 7, adsorption efficiency of MO increases constantly with increasing of dosage of composite materials. When the dosage of b-CD-GO-DE is 0.020 g cm-3, the removal efficiency of MO is the maximum and the value can be obtained at 95.90%. This is mainly attributed to that the number of available adsorption sites increases and the contact area also increases, which leads to the surface of b-CD-GO-DE providing more hydroxyl groups, and they occurred ion exchange with MB dye molecules to form hydrogen bond. Meanwhile, b-CD provides numerous cavities to parcel MB molecules.

Fig. 7 Effect of the dosage of b-CD-GO-DE on the adsorption efficiency of MB

However, with increasing of b-CD-GO-DE dosage, the adsorption efficiency of MB tends to horizontal. It might be attributed to increase that adsorbent dose leads to the adsorption site occurred aggregating or overlapping. Therefore, 0.020 g cm-3 was chosen to be the optimum dosage in this work.

Effect of the temperature on the adsorption efficiency of MB solution The experimental conditions were: 0.020 g cm-3 of dosage of b-CD-GO-DE, adsorption time of 6 h, and 100 mg dm-3 of MB solution. Effect of temperature on the adsorption efficiency of MB solution is shown in Fig. 8. As can be seen from Fig. 8, initially, the MB adsorption

Fig. 6 Adsorption mechanism of b-CD-GO-DE

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Fig. 8 Effect of temperature on the adsorption efficiency of MB solution

Fig. 9 Effect of the contact time on the adsorption efficiency of MB solution

efficiency increases little with increasing of temperature from 25 to 55 C. However, the adsorption efficiency of MB sudden increases obviously when the temperature rises to 65 C. This is mainly due to MB molecular motion increased with the temperature increased, so the adsorbent adsorption efficiency is accelerated. With increasing temperature up to the 85 C, the adsorption efficiency of MB tends to horizontal. It is attributed to the molecular disorder weakened and weak of intermolecular attraction. It also indicated that the process of adsorption system is endothermic. The maximum adsorption efficiency was obtained at 65 C. Therefore, 65 C was chosen to be the optimum temperature for further study.

mainly due to that the adsorbent has reached the saturated adsorption. Therefore, 3 h is selected as the optimum contact time in this study.

Effect of contact time on the adsorption efficiency of MB solution The experimental conditions were: 0.020 g cm-3 of dosage of b-CD-GO-DE, temperature of 65 C, and 100 mg dm-3 of MB solution. Effect of contact time on the adsorption efficiency of MB was investigated and result is shown in Fig. 9. As can be seen from Fig. 9, at initial adsorption stage, the adsorption efficiency increases rapidly with time prolonging and then increases slowly, and when time reached 3 h, the adsorption system reaches adsorption equilibrium eventually. The initial rapid adsorb is mainly because the surface of b-CD-GO-DE provide void adsorption sites and this can make MB molecules attached on the adsorbent. Meanwhile, The surface of b-CD-GO-DE contains numerous of carboxyl and hydroxyl groups, which occurred ion exchange with MB dye molecules to form hydrogen bond and b-CD has a large number of cavities; these cavities can parcel MB molecular to form host–guest inclusion compound. When the adsorption of time is more than 3 h, the adsorption equilibrium is reached. It might be

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Adsorption kinetics Kinetic models were used to examine the rate of the adsorption process and propose potential rate-controlling step. To investigate the mechanism and dynamic characteristic of adsorption process, pseudo-second-order [23] kinetic model was used to fit the experimental data. Because it provides a more appropriate illustrate. The adsorption kinetics curve of MB dyes onto b-CD-CMC-GO at the optimal conditions is the same, as shown in Fig. 9. The pseudo-second-order kinetic model is described as in the following equation: t 1 t ¼ þ ; 2 Qt K2 Qe Qe

ð1Þ

where Qt is the adsorption quantity at time t (mg g-1); K2 is the pseudo-second-order adsorption rate constant (g mg-1 min-1); and Qe is the adsorption quantity when adsorption process achieve equilibrium (mg g-1). Potting of t/Qt versus t gives a linear relationship, as shown in Fig. 10. The values of K2 and Qe were obtained from the slope and intercept of the line, respectively. The kinetic parameters are listed in Table 1. From Table 1, it can be obviously seen that it can be obviously seen that the correlation coefficient R2 = 0.9901 and pseudo-second-order rate constant -1 -1 K = 0.0035 g mg min . It indicates that the adsorption data are well represented by pseudo-second-order kinetic model and the rate-limiting step might be due to chemical adsorption. Meanwhile, the theoretical measured Qe = 5.90 mg g-1 is more agree with the actual calculated

b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its…

adsorption. Plotting 1/Qe against 1/Ce gives a straight line with intercept and slope equal to 1/Qm and 1/(bQm), as shown in Fig. 11a. Freundlich isotherm is an empirical equation describing that the adsorption surface becomes heterogeneous during the adsorption process. The linear form of the Freundlich model could be represented as follows [25]: 1 log Qe ¼ log Kf þ log Ce ; n

Fig. 10 Pseudo-second-order adsorption kinetic Table 1 Pseudo-second-order kinetic parameters for MB adsorption onto b-CD-GO-DE K/g mg-1 min-1

Qe/mg g-1

R2

Qcal/mg g-1

0.0035

5.90

0.9901

6.12

Qcal = 6.12 mg g-1. It also illustrates that pseudo-secondorder kinetics model can reflect the adsorption mechanism more appropriately and contains all the process of adsorption, such as occurred ion exchange to form hydrogen bond between adsorbent and adsorbate.

Adsorption isotherm Adsorption isotherms are generally to describe how adsorbates interact with adsorbents. Some specific parameters can instructions adsorption system. The adsorption of MB by b-CD-GO-DE was carried out at the optimum conditions and at different initial concentrations. The two well-known adsorption isotherm equations, Langmuir and Freundlich isotherm models were selected to fit the equilibrium adsorption data, respectively. The adsorption amount of MB is increased with increasing the initial concentrations of MB solution. The linear form of the Langmuir isotherm equation could be expressed as follows [24]: 1 1 1 ¼ þ ; Qe Qm bQm Ce

ð2Þ

where Qe is the adsorption quantity at adsorption equilibrium (mg g-1), Qm is maximum adsorption capacity (mg g-1), Ce is the equilibrium concentration of MB dye solution (mg dm-3), and b is the Langmuir binding constant (dm3 mg-1), which is related to the energy of

ð3Þ

where Kf and n are Freundlich constants related to adsorption capacity and the adsorption intensity, respectively. Plotting logQe against logCe gives a straight line with intercept and slope equal to logKf and 1/n. It is described in Fig. 11b. The value of Freundlich constant 1/ n predicts the applicability of the adsorbent for a particular adsorbate. The Freundlich constant 1/n between 0 and 1 is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero. If the value of 1/n is smaller than 1, it indicates that the adsorption system can be well represented by Langmuir isotherm. While the value of 1/n higher than 1 is indicative of cooperative adsorption [26]. The entire isotherm fitted parameters and the theory data were calculated and also summarized in Table 2. From Table 2, it can be seen that the Langmuir isotherm model with correlation coefficient R2 = 0.9952 matches experimental data better than the Freundlich isotherm model with correlation coefficient R2 = 0.9647; it indicated that Langmuir isotherm model fits the experimental data more suitable to describe the adsorption system. The maximum adsorption capacity Qm of MB on b-CD-GO-DE from Langmuir isotherm model is 110.50 mg g-1. It explains that the b-CD-GO-DE has well adsorbed ability to MB. At this time, the value of 1/n is also found to be lower than 1, indicating that the adsorption intensity of the system and adsorption of MB on b-CD-GO-DE can also be fitted to Langmuir isotherm model. The adsorption process of MB on b-CD-GO-DE contains a variety of ways, such as on the surface of b-CD-GO-DE contains numerous of carboxyl and hydroxyl groups, which occurred ion exchange with MB dye molecules to form hydrogen bond. Moreover, the b-CD-GO-DE material contains a large number of cavities of b-CD; these cavities can parcel MB molecular to form host–guest inclusion compound. Therefore, b-CD-GO-DE composite materials can be adsorbed MB dye molecular effectively.

Desorption and reuse The regeneration and recycling ability are significant for the practical application of adsorbents. Adsorbents have excellent adsorption capacity as well as high desorption

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Fig. 11 Langmuir isotherm model (a) and Freundlich isotherm model (b) Table 2 Adsorption isotherms parameters for MB dye adsorption onto b-CD-GO-DE composite Langmuir -1

Freundlich 3

Qm/mg g

B/dm mg

110.50

0.0443

-1

R

2

0.9952

Kf

1/n

R2

0.8402

0.9382

0.9647

property will reduce the overall cost and economic and environmental protection. To evaluate the possibility of desorption and reusability of b-CD-GO-DE as an adsorbent, five consecutive adsorption–desorption cycle experiments were performed. The results are shown in Fig. 12.

From Fig. 12, it can be seen obviously that the adsorption capacity of MB dye decreased with increasing cycle number. The adsorption capacity changed from 110.50 to 59.41 mg g-1. The adsorption is reduced after regeneration, which attributes to slow dissolution of b-CD-GO-DE in acidic or alkali solution during the process of elution. The results show that b-CD-GO-DE can be economically and effectively recycled for removal of MB dye solutions and the adsorbents can be reused.

Comparison with various adsorbents for removal of MB The maximum adsorption capacities (Qm) of MB onto bCD-GO-DE were compared with other adsorbents [27–31] for removal of MB. The results are given in Table 3. It can be seen that b-CD-GO-DE shows higher adsorption capacity than other adsorbents. It reflected that the b-CDGO-DE materials can be considered as an ideal adsorbent for removal of MB from dye solution.

Table 3 Comparison with other adsorbent for removal of MB Adsorbent

Fig. 12 Effect of recycle times of b-CD-GO-DE on the adsorption efficiency

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Qm/ mg g-1

References

Magnetic rectorite

31.18

[27]

Raw ball clay

34.65

[28]

Fe3O4/C core–shell particles Magnetic chitosan

44.38 60.40

[29] [30]

Montmorillonite modified with iron oxide

69.11

[4]

Chitosan/bentonite

95.24

[31]

b-CD-GO-DE

110.50

This work

b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its…

Conclusion On the whole, a novel b-cyclodextrin–graphene oxide–diatomaceous earth material (b-CD-GO-DE) was prepared and its application as excellent adsorbents was carried out for adsorption of MB in aqueous solution. The adsorption experiment for removal of MB was investigated in detail. The highest adsorption efficiency can reach 98.5% at 0.02 g cm-3 dosage of b-CD-GO-DE, the temperature of 65 C, and time of 3 h. Adsorption kinetics and adsorption isotherm were researched to analysis the adsorption system. Pseudo-second-order kinetics model can describe the adsorption process appropriately. The equilibrium data were fitted well with Langmuir isotherm model, and the maximum adsorption capacity of MB reached 110.50 mg g-1. The adsorbent has good regeneration performance. The proposed method shows that the b-CD-GODE could be considered as an ideal adsorbent for adsorb of MB in wastewater with satisfactory result.

Experimental Graphite powder, concentrated sulfuric acid (H2SO4), sodium nitrate (NaNO3), hydrogen chloride (HCl), dibutyl tin laurate (T-12), N,N-dimethylformamide (DMF), isophorone diisocyanate (IPDI, purity C 99.5% and –NCO content C 37.5%), concentration of 30% hydrogen peroxide (H2O2), potassium permanganate (KMnO4), b-cyclodextrin (b-CD), and diatomaceous earth (DE) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China). Sodium hydroxide (NaOH), hydrogen chloride (HCl), and methylene blue (MB) were obtained from three-reagent factory in Shanghai. FT-IR spectra of samples were recorded at the range from 4000 to 400 cm-1 on a KBr powder with Madison– Nicolet spectrometer (AVATAR 360, Nicolet, Madison, USA). A minimum of 32 scans was signal-averaged with a resolution of 2 cm-1 in the above ranges. The fracture surface of sample was investigated using a Hitachi S-4800 with a 15-kV accelerating voltage with a field emission Scanning Electron Microscope (SEM) (S-4800, Hitachi Corp., Tokyo, Japan). Transmission electron microscopy (TEM) was operated on a Philips TECNAI-12 with an acceleration voltage of 120 kV. X-ray diffraction (XRD) patterns were recorded by the reflection scan with nickelfiltered Cu-Ka radiation (D8, Bruker-AXS, Germany). The X-ray generator was operated at 40 kV and 70 mA. The scanning speed was 4 min-1 over the range from 5 to 80. Thermogravimetric analysis (TG) was recorded on a Netzsch (Germany) STA 449C instrument. The air flow is 50 cm3 min-1. The programmed heating range was from

room temperature to 800 C at a heating rate of 10 C min-1 under a nitrogen atmosphere. The measurement was taken with 6–10-mg sample. The concentration of dye solution was determined using visible spectrophotometer (722 s, Edge light technology co., LTD, Shanghai, China).

Preparation of graphene oxide (GO) GO was prepared by a modification of Hummers’ method [32]. Thus, 1 g graphite powder and 0.5 g NaNO3 were dissolved in 98% H2SO4 (23 cm3) in a 250 cm3 three-necked flask kept below 4 C using an ice-water bath. The solution was stirred vigorously and 3 g KMnO4 powder was added slowly and uniformly over 1 h whilst the temperature was kept below 15 C. After addition of all the KMnO4 powder, the reaction temperature was increased to 35 C with constant stirring. After 2 h, 46 cm3 distilled water was added gradually; the solution was brown at this time. The reaction temperature was increased to 98 C for 30 min, during which the solution changed color to bright yellow. The solution was diluted with 140 cm3 of distilled water and then 30% H2O2 (10 cm3) was added. The mixture was left to stand for 1 h and, after centrifugal separation of the supernatant, the precipitate was washed with 5% hydrochloric acid solution (10 cm3) until the pH value of the washings was 5 or 6. The solid was dried at 60 C, ground, and sieved to afford GO.

Synthesis of b-CD-GO-DE composite material The b-CD-GO-DE was prepared in three steps: 1.

2.

3.

GO (0.50 g) was dispersed in dry 50 cm3 DMF in an ultrasound bath. After centrifugal separation, the supernatant was transferred to a 250 cm3 three-necked flask. Then, 7.5 cm3 IPDI and 2 drops of T-12 catalyst were added and the mixture was heated for 3 h under nitrogen protection at 80 C. b-CD (8.28 g) was dispersed in 50 cm3 DMF and the solution was added to the above reaction mixture. After reaction for 3.5 h in a water bath at 70 C, the resultant product was washed and dried at 50 C in a vacuum drying oven. The b-CD-GO obtained was ground ready for use. Diatomite (DE, 15.5 g) in 120 cm3 NaOH solution (2.5 mol dm-3) was stirred magnetically for 2 h at 100 C. The supernatant was removed and the residue was centrifuged and washed with distilled water several times. The solid was ground to afford activated diatomite solid, which was then dispersed in deionized water. b-CD-GO (5.15 g) and cetyltrimethylammonium bromide (CTMAB, 0.5 g) were added. After reaction for 5 h, the final composite material b-CD-GO-DE was obtained. The synthetic route is shown in Fig. 13.

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Fig. 13 Synthetic route of b-CD-GO-DE

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b-Cyclodextrin–graphene oxide–diatomaceous earth material: preparation and its…

Dye adsorption experiments

References

To test the performance of b-CD-GO-DE as a dye adsorbent, adsorption experiments were carried out with of MB. Thus, a suitable amount of b-CD-GO-DE in 10 cm3 of 100 mg dm-3 MB aqueous solution was left a certain period of time to allow static adsorption. After centrifugal separation, the supernatant solution was subjected to visible spectrophotometry at kmax = 664 nm. The concentration of supernatant solution was then obtained via the standard curve of MB. The adsorption efficiency (D) of adsorbed MB on b-CD-GO-DE was calculated using the following equation:

1. Weng CH, Pan YF (2007) J Hazard Mater 144:355 2. Al-Degs Y, Khraisheh MAM, Allen SJ, Ahmad MN (2000) Water Res 34:927 3. Peng YG, Chen DJ, Ji JL, Kong Y, Wan HX, Yao C (2013) Appl Clay Sci 74:81 4. Cottet L, Almeida CAP, Naidek N, Viante MF, Lopes MC, Debacher NA (2014) Appl Clay Sci 95:25 5. Dabrowski A, Podkoscielny P, Hubicki Z, Barczak M (2005) Chemosphere 58:1049 6. Hong S, Wen C, He J, Gan FX, Ho YS (2009) J Hazard Mater 167:630 7. Ozacar M, Sengil IA (2005) Bioresour Technol 96:791 8. Wang SB, Boyjoo Y, Choueib A, Zhu ZH (2005) Water Res 39:129 9. Zhao H, Qiu F, Yan J, Wang J, Li X, Yang D (2016) Appl Clay Sci 121–122:137 10. Yan J, Zhu Y, Qiu F, Zhao H, Yang D, Wang J, Wen W (2016) Chem Eng Res Des 106:168 11. Yan J, Li X, Qiu F, Zhao H, Yang D, Wang J, Wen W (2016) Mater Technol 31:406 12. Lee CG, Wei SD, Kysar JW, Hone J (2008) Science 321:385 13. Balandin AA, Ghosh S, Bao WZ, Calizo I, Teweldebrhan D, Miao F, Lau CN (2008) Nano Lett 8:902 14. Chen Y, Qi YY, Tai ZX, Yan XB, Zhu FL, Xue QJ (2012) Eur Polym J 48:1026 15. Compton OC, Jain B, Dikin DA, Abouimrane A, Amine K, Nguyen ST (2011) ACS Nano 5:4380 16. He K, Qiu F, Qin J, Yan J, Yang D (2014) J Ind Eng Chem 20:1293 17. Yuan J, Qiu F, Li P (2017) J Iran Chem Soc 14:1827 18. Wang J, Qiu F, Wu H, Li X, Zhang T, Niu X, Yang D (2017) Spectrochim Acta A 179:163 19. Guo YJ, Guo SJ, Ren JT, Zhai YM, Dong SJ, Wang EK (2010) ACS Nano 4:4001 20. Sljivic M, Smiciklas I, Pejanovic S, Plecas I (2009) Appl Clay Sci 43:33 21. Tsai WT, Hsien KJ, Chang YM, Lo CC (2005) Bioresource Technol 96:657 22. Khraisheh MAM, Al-Degs YS, Mcminn WAM (2004) Chem Eng J 99:177 23. Ho YS, McKay G (1999) Process Biochem 34:451 24. Langmuir I (1916) J Am Chem Soc 38:2221 25. Freundlich H (1928) Colloid and capillary chemistry. E.P. Dutton and Co., New York 26. Fytianos K, Voudrias E, Kokkalis E (2000) Chemosphere 40:3 27. Wu DL, Zheng PW, Chang PR, Ma XF (2011) Chem Eng J 174:489 28. Auta M, Hameed B (2012) Chem Eng J 198:219 29. Zhang ZY, Kong JL (2011) J Hazard Mater 193:325 30. Fan LL, Luo CN, Li XJ, Lu FG, Qiu HM, Sun M (2012) J Hazard Mater 215:272 31. Bulut Y, Karaer H (2015) J Dispers Sci Technol 36:61 32. Hummers WS Jr, Offeman RE (1958) J Am Chem Soc 80:1339

D¼

C0  Ct  100%; C0

ð4Þ

where D is the adsorption efficiency of MB on b-CD-GODE (%); C0 is the initial concentration of the MB dye solution; and Ct is the concentration of the MB dye solution at time t (mg dm-3). The adsorption capacity (Qt) of adsorbed MB on b-CDGO-DE (mg g-1) was calculated using the following equation: Qt ¼

ðC0  Ct Þ  V; M

ð5Þ

where Qt is the adsorption capacity of adsorbed MB dye on b-CD-GO-DE (mg g-1); M is the mass of b-CD-GO-DE (g); and V is the volume of the MB dye solution (dm3).

Desorption and regeneration experiment An excellent adsorbent not only has good adsorption performance but also has a better desorption and regeneration performance. The desorption experiment aimed to assess the potential reusability of the b-CD-GO-DE composite material. After adsorption of MB, the b-CD-GO-DE was separated from the aqueous solution by centrifugal separation and washed with 60 cm3 of 1 mol dm-3 HCl three times, 60 cm3 of 1 mol dm-3 NaOH three times, and 50 cm3 of ethanol two times, respectively. The adsorbent was then dried in an oven. The b-CD-CMC-GO composite material was subjected to the above experiment five times under the same adsorption conditions. Acknowledgements This project was supported by the National Natural Science Foundation of China (U1507115) and the Innovation Program for Graduate Education of Jiangsu Province (KYLX_1063).

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