- Email: [email protected]
The exploration of a new adsorbent as MnO2 modified expanded graphite
Materials Letters 110 (2013) 69–72
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
The exploration of a new adsorbent as MnO2 modified expanded graphite Hongyun Jin a,b,n, Jiao Yuan a, Hongyan Hao a, Zhengjia Ji a, Min Liu a, Shuen Hou a,b,n a b
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 May 2013 Accepted 10 July 2013 Available online 27 July 2013
MnO2-modified Expanded Graphite (MnO2/EG) nano-composites were prepared through redoxprecipitation reaction between EG, MnSO4 solution and KMnO4 solution at 40 1C. The X-ray powder diffraction (XRD) results showed that the surface of EG was grafted with γ-MnO2. Meanwhile, a Field Scanning Electron Microscope (FSEM) was employed to analyze the morphology of the as-modified expanded graphite. Nano spindles (with a length of 30–80 nm and a diameter of 10–30 nm) were observed on the surface and interspaces of EG. Fourier transform infrared (FTIR) spectra verified the presence of new functional groups on the surface of the MnO2/EG which were not seen on EG. The superior adsorbent properties of the as-synthesized MnO2/EG proved highly effective in absorbing Cr(VI), where the removal rate reached 90.35% and the absorbed amount reached about 0.3011 mg/g. Improved properties for adsorbing Cr(VI) from polluted water were observed in MnO2/EG, and the absorbed amount at equilibrium was more than twice as much as that of EG. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nanoparticles MnO2-modified expanded graphite FTIR Chromium (VI) Adsorption
1. Introduction Discarded pollutant materials, such as heavy metal ions from industrial effluents, threaten both the environment and public health. Among heavy metals, the toxic pollutant chromium has become increasingly present in natural water [1]. Heavy metal ions can be removed through various methods [2–4]. Compared with other conventional methods for removing heavy metals from polluted water, the adsorption method has shown various advantages [5]. Among the wide-range of adsorbents available [6,7], EG and their composites have been demonstrated as one of the most effective and reliable due to their porous structure, high surface area and presence of surface functional groups [8]. So it is used for purification, decolorization and the removal of heavy metal ions in the treatment of wastewater. Manganese oxide with different nanostructures has also been widely used as a selective heterogeneous adsorbent, in particular mesoporous [9], urchins [10] and nanorods [11] are well-known for their ability to efficiently remove heavy metal ions from polluted water. In this work, a MnO2/EG composite was obtained using a facile and efficient method. This sample was subsequently used to adsorb Cr(VI). The experimental parameters for adsorption were
n Corresponding authors at: Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China. Tel.: +86 134 761 18841. E-mail addresses: [email protected] (H. Jin), [email protected] (S. Hou).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.07.042
optimized and the adsorption mechanism was elucidated using XRD, FSEM and FTIR results. 2. Experimental section Materials: The MnO2/EG nano-composites were synthesized by the redox-precipitation method. Firstly, a mixture of 60 mL MnSO4 solution (0.1 mol/L) and 0.25 g EG was placed in a thermostatic bath at 40 1C for 10 min. Then, 15 mL KMnO4 (0.1 mol/L) was added to the above solution mixture and stirred for 20 min. The resulting products were then heated for 2 h at 40 1C. Finally, the products were filtered and washed several times with deionized water and dried at 60 1C for 8 h in a vacuum oven. Characterization: The crystalline phases of the samples were determined by XRD (D8-FOCUS) with Cu Kα radiation (λ ¼0.15406 nm). FSEM (SU8010) was used to analyze the morphology of the samples, where the composite particles were coated with gold and the images were then taken at 15.0 kV. The FTIR spectra were recorded in KBr pellets with a Bruker Vertex 70 instrument in a range between 400 and 4000 cm 1. Adsorption experiments: Batch adsorption experiments were performed in 250 mL flasks, each containing a 50 mL Cr(VI) ions solution. A standard solution of Chromium (VI) (100 mg/L) was prepared by dissolving 0.2829 g K2Cr2O7 in 1000 mL of distilled water. The experiments were executed at the adsorbent dose of EG and MnO2/EG ranged from 0.1 to 0.6 g in an initial metal
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H. Jin et al. / Materials Letters 110 (2013) 69–72
concentration of 2 mg/L Cr(VI) at pH of 5.0, the mixture were shaken in a controlled shaker (THZ-82) at 200 rpm at 30 1C for 90 min.. Afterwards, EG and MnO2/EG were separated from the solution using filter paper, and the amount of remaining metal ion concentration was determined using an ultraviolet spectrophotometer (A UV-7504). The amount of metal ions adsorbed on the
adsorbent at adsorption equilibrium was calculated according to: qt ¼
ðC o C t ÞV m
ð1Þ
where, qt (mg/g) is the adsorbed amounts at contact time t (min) and Co and Ct (mg/L) are the initial and equilibrium concentrations of metal ion in the solution, respectively. V (L) is the volume of the solution. Finally, m (g) is the amount of adsorbent added to the solution.
3. Results and discussion
Fig. 1. XRD patterns of EG, γ-MnO2 and MnO2/EG.
XRD analysis: As seen in Fig. 1, the XRD analyses exhibited the same location for the diffraction peaks of both EG and MnO2/EG, which was at 2θ around 26.81and 54.71, which could be indexed to EG. In the EG samples treated by KMnO4 and MnSO4 solution, four diffraction peaks were found in the same location for MnO2/EG and MnO2, they could be indexed to γ-MnO2. It was found that no new diffraction peaks were appeared by XRD after EG samples treated by KMnO4 and MnSO4 solution, proving that MnO2 and EG were joined together by physical bonding. Moreover, the line broadening observed in the XRD patterns suggested that these samples were in a poor crystalline state with a short-range crystal form. Such a low degree of crystallization could be attributed to the reaction. As KMnO4 was added at a relatively low temperature (about 40 1C) and the reaction rate was relatively high. The morphology of MnO2/EG: Fig. 2 shows FSEM images of MnO2/EG nano-composites. As illustrated, EG surface was relatively smooth (Fig. 2a). After EG was treated with KMnO4 and MnSO4 solution, it could be seen that MnO2 nano particles not only grafted on the surface, but also grafted in the interspaces of EG. Furthermore, the MnO2 nano particles grafted on the EG composite showed good dispersion properties (Fig. 2b). Fig. 2d shows that the detected elements on the surface of MnO2/EG are Mn, and O. The element of Mn indicated that MnO2 oxide nanoparticles were coated on the surface of EG. It was also observed that MnO2 dispersed on the EG surface showing
Fig. 2. FSEM images of EG, MnO2/EG and EDS of MnO2/EG.
H. Jin et al. / Materials Letters 110 (2013) 69–72
71
Fig. 3. FTIR spectra of EG and MnO2/EG.
spindle-like morphologies with a diameter of 10–30 nm and a length of 30–80 nm (Fig. 2c, d). The length–diameter ratio of the nano spindle was calculated at approximately 3:1. The nano size MnO2 particles could therefore offer a larger specific surface area, providing easier access for electrolyte ions and electrons. FTIR analysis: To elucidate the adsorption mechanism, FTIR spectra of EG and MnO2/EG are presented in Fig. 3. The broad band at 3450 cm 1 and the band at 1634 cm 1 found in each sample could be attributed to the stretching vibrations of intra and intermolecular hydrogen bonded –OH and CQC, respectively. Furthermore, the bands around 2924 and 2854 cm 1 corresponded to the CH2 stretching vibrations, while the characteristic peaks appeared for CQO group at 1758 cm 1. The bands between 1461–1300 cm 1 indicated the presence of C–H bending in the –CH3 group, while the bands at 1124 were attributed to the –CO stretching for secondary alcohol. As EG was prepared by a KMnO4 oxidation process (Fig. 3), the EG showed an absorption peak at 526 cm 1, which was characteristic for Mn–O undergoing stretching vibration. The changes occurred on EG after the samples were treated by KMnO4 and MnSO4. Compared with the EG sample, the adsorption band of MnO2/EG at 1758 cm 1 and 1500–1200 cm 1 disappeared completely, indicating that one-end of MnO2 had been grafted on the surface of EG through CQO groups and the C– H bending of –CH3 groups. The bands at 570 and 526 cm 1 were also ascribed to the stretching vibration of Mn–O. The effect of adsorbent dose: The effect of EG and MnO2/EG dose on the adsorption of Cr(VI) from aqueous solutions was investigated. As shown in Fig. 4, the removal efficiency of Cr(VI) by MnO2/EG increased sharply as the sorbent dose increased from 0.1 g (53.57%) to 0.3 g (90.35%). As the adsorbent additive amount increased further, the removal rate of Cr(VI) rose slowly and then reached an almost constant value of 95.9% at 0.6 g. However, as expected, the adsorption capacities decreased with increasing adsorbent mass. When the adsorbent doses were at 0.1, 0.3 and 0.6 g EG and the MnO2/EG adsorbed amounts at equilibrium were at 0.2785, 0.1583, 0.1136 and 0.5357, 0.3011, 0.1648 mg/g, respectively. Considering the factors of adsorbed amounts and removal efficiency, the optimum amount of adsorbent dose was selected as 0.3 g. Compared with MnO2/EG, EG exhibited much lower removal efficiency and adsorbed amounts for Cr(VI). However, impregnation with MnO2 significantly enhanced the adsorption capacity of the EG toward Cr(VI). I think there are two main reasons for this phenomenon. Firstly, this improvement could be attributed to the larger surface area of MnO2/EG that provides higher micropore and mesopore volumes. Secondly, MnO2 impregnation may have
Fig. 4. The effect of adsorbent dose on the adsorption of Cr(VI) by MnO2/EG and EG. (The dotted lines and solid lines correspond to qt and Cr(VI) removal efficiency, respectively.)
also introduced more functional groups such as carboxyls and phenols to the carbon surface, which could provide more adsorption sites for Cr(VI).
4. Conclusions In this work, MnO2-modified Expanded Graphite has been prepared by the reaction between Expanded Graphite, MnSO4 solution and KMnO4 solution. The XRD, FSEM and FTIR results demonstrated that the surface of the EG flakes was successfully modified. Some nano spindle-like MnO2 (with a length of 30–80 nm and a diameter of 10–30 nm) were dispersed on the surface and interspaces of EG. The obtained material possessed a much larger surface area and more functional groups such as carboxyls and phenols, which could provide more adsorption sites for Cr(VI) and enhance the adsorbed amounts. Under the optimum parameters of the adsorption experiment (Co ¼2 mg/L, pH ¼ 5, T¼ 30 1C, t¼90 min and m¼ 0.3 g) the removal rate and the adsorbed amounts reached 90.35% and 0.3011 mg/g, respectively.
Acknowledgment The work was carried out under the financial of China (No: NSFC51102218), the Wuhan Scientific and technological project (No: 201210321099) and the Fundamental Research Funds for the Central Universities (Nos: CUG120402 and CUG120118). References [1] Wu Y, Luo H, Wang H, Wang C, Zhang J, Zhang Z. Adsorption of hexavalent chromium from aqueous solutions by graphene modified with cetyltrimethylammonium bromide. Journal of Colloid and Interface Science 2013;394: 183–91. [2] Kim J, Benjamin MM. Modeling a novel ion exchange process for arsenic and nitrate removal. Water Research 2004;38:2053–62. [3] Teychene B, Collet G, Gallard H, Croue J-P. A comparative study of boron and arsenic (III) rejection from brackish water by reverse osmosis membranes. Desalination 2013;310:109–14. [4] Zaw M, Emett MT. Arsenic removal from water using advanced oxidation processes. Toxicology Letters 2002;133:113–8. [5] Pattanayak J, Mondal K, Mathew S, Lalvani SB. A parametric evaluation of the removal of As(V) and As(III) by carbon-based adsorbents. Carbon 2000;38: 589–96. [6] Das NN, Konar J, Mohanta MK, Upadhaya AK. Synthesis, characterization and adsorptive properties of hydrotalcite-like compounds derived from titanium rich bauxite. Reaction Kinetics Mechanisms and Catalysis 2010;99:167–76.
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H. Jin et al. / Materials Letters 110 (2013) 69–72
[7] Guedidi H, Reinert L, Leveque J-M, Soneda Y, Bellakhal N, Duclaux L. The effects of the surface oxidation of activated carbon, the solution pH and the temperature on adsorption of ibuprofen. Carbon 2013;54:432–43. [8] Zhu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, et al. Graphene and graphene oxide: synthesis, properties, and applications. Advanced Materials 2010;22: 3906–24. [9] Yu J, Zhao T, Zeng B. Mesoporous MnO2 as enzyme immobilization host for amperometric glucose biosensor construction. Electrochemistry Communications 2008;10:1318–21.
[10] Zhang J, Chu W, Jiang J, Zhao XS. Synthesis, characterization and capacitive performance of hydrous manganese dioxide nanostructures. Nanotechnology 2011;22:125703. [11] Jia Y, Xu J, Zhou L, Liu H, Hu Y. A simple one step approach to preparation of gamma-MnOOH multipods and beta-MnO2 nanorods. Materials Letters 2008;62:1336–8.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
The exploration of a new adsorbent as MnO2 modified expanded graphite Hongyun Jin a,b,n, Jiao Yuan a, Hongyan Hao a, Zhengjia Ji a, Min Liu a, Shuen Hou a,b,n a b
Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 May 2013 Accepted 10 July 2013 Available online 27 July 2013
MnO2-modified Expanded Graphite (MnO2/EG) nano-composites were prepared through redoxprecipitation reaction between EG, MnSO4 solution and KMnO4 solution at 40 1C. The X-ray powder diffraction (XRD) results showed that the surface of EG was grafted with γ-MnO2. Meanwhile, a Field Scanning Electron Microscope (FSEM) was employed to analyze the morphology of the as-modified expanded graphite. Nano spindles (with a length of 30–80 nm and a diameter of 10–30 nm) were observed on the surface and interspaces of EG. Fourier transform infrared (FTIR) spectra verified the presence of new functional groups on the surface of the MnO2/EG which were not seen on EG. The superior adsorbent properties of the as-synthesized MnO2/EG proved highly effective in absorbing Cr(VI), where the removal rate reached 90.35% and the absorbed amount reached about 0.3011 mg/g. Improved properties for adsorbing Cr(VI) from polluted water were observed in MnO2/EG, and the absorbed amount at equilibrium was more than twice as much as that of EG. & 2013 Elsevier B.V. All rights reserved.
Keywords: Nanoparticles MnO2-modified expanded graphite FTIR Chromium (VI) Adsorption
1. Introduction Discarded pollutant materials, such as heavy metal ions from industrial effluents, threaten both the environment and public health. Among heavy metals, the toxic pollutant chromium has become increasingly present in natural water [1]. Heavy metal ions can be removed through various methods [2–4]. Compared with other conventional methods for removing heavy metals from polluted water, the adsorption method has shown various advantages [5]. Among the wide-range of adsorbents available [6,7], EG and their composites have been demonstrated as one of the most effective and reliable due to their porous structure, high surface area and presence of surface functional groups [8]. So it is used for purification, decolorization and the removal of heavy metal ions in the treatment of wastewater. Manganese oxide with different nanostructures has also been widely used as a selective heterogeneous adsorbent, in particular mesoporous [9], urchins [10] and nanorods [11] are well-known for their ability to efficiently remove heavy metal ions from polluted water. In this work, a MnO2/EG composite was obtained using a facile and efficient method. This sample was subsequently used to adsorb Cr(VI). The experimental parameters for adsorption were
n Corresponding authors at: Faculty of Material Science and Chemistry, China University of Geosciences, Wuhan 430074, PR China. Tel.: +86 134 761 18841. E-mail addresses: [email protected] (H. Jin), [email protected] (S. Hou).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.07.042
optimized and the adsorption mechanism was elucidated using XRD, FSEM and FTIR results. 2. Experimental section Materials: The MnO2/EG nano-composites were synthesized by the redox-precipitation method. Firstly, a mixture of 60 mL MnSO4 solution (0.1 mol/L) and 0.25 g EG was placed in a thermostatic bath at 40 1C for 10 min. Then, 15 mL KMnO4 (0.1 mol/L) was added to the above solution mixture and stirred for 20 min. The resulting products were then heated for 2 h at 40 1C. Finally, the products were filtered and washed several times with deionized water and dried at 60 1C for 8 h in a vacuum oven. Characterization: The crystalline phases of the samples were determined by XRD (D8-FOCUS) with Cu Kα radiation (λ ¼0.15406 nm). FSEM (SU8010) was used to analyze the morphology of the samples, where the composite particles were coated with gold and the images were then taken at 15.0 kV. The FTIR spectra were recorded in KBr pellets with a Bruker Vertex 70 instrument in a range between 400 and 4000 cm 1. Adsorption experiments: Batch adsorption experiments were performed in 250 mL flasks, each containing a 50 mL Cr(VI) ions solution. A standard solution of Chromium (VI) (100 mg/L) was prepared by dissolving 0.2829 g K2Cr2O7 in 1000 mL of distilled water. The experiments were executed at the adsorbent dose of EG and MnO2/EG ranged from 0.1 to 0.6 g in an initial metal
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H. Jin et al. / Materials Letters 110 (2013) 69–72
concentration of 2 mg/L Cr(VI) at pH of 5.0, the mixture were shaken in a controlled shaker (THZ-82) at 200 rpm at 30 1C for 90 min.. Afterwards, EG and MnO2/EG were separated from the solution using filter paper, and the amount of remaining metal ion concentration was determined using an ultraviolet spectrophotometer (A UV-7504). The amount of metal ions adsorbed on the
adsorbent at adsorption equilibrium was calculated according to: qt ¼
ðC o C t ÞV m
ð1Þ
where, qt (mg/g) is the adsorbed amounts at contact time t (min) and Co and Ct (mg/L) are the initial and equilibrium concentrations of metal ion in the solution, respectively. V (L) is the volume of the solution. Finally, m (g) is the amount of adsorbent added to the solution.
3. Results and discussion
Fig. 1. XRD patterns of EG, γ-MnO2 and MnO2/EG.
XRD analysis: As seen in Fig. 1, the XRD analyses exhibited the same location for the diffraction peaks of both EG and MnO2/EG, which was at 2θ around 26.81and 54.71, which could be indexed to EG. In the EG samples treated by KMnO4 and MnSO4 solution, four diffraction peaks were found in the same location for MnO2/EG and MnO2, they could be indexed to γ-MnO2. It was found that no new diffraction peaks were appeared by XRD after EG samples treated by KMnO4 and MnSO4 solution, proving that MnO2 and EG were joined together by physical bonding. Moreover, the line broadening observed in the XRD patterns suggested that these samples were in a poor crystalline state with a short-range crystal form. Such a low degree of crystallization could be attributed to the reaction. As KMnO4 was added at a relatively low temperature (about 40 1C) and the reaction rate was relatively high. The morphology of MnO2/EG: Fig. 2 shows FSEM images of MnO2/EG nano-composites. As illustrated, EG surface was relatively smooth (Fig. 2a). After EG was treated with KMnO4 and MnSO4 solution, it could be seen that MnO2 nano particles not only grafted on the surface, but also grafted in the interspaces of EG. Furthermore, the MnO2 nano particles grafted on the EG composite showed good dispersion properties (Fig. 2b). Fig. 2d shows that the detected elements on the surface of MnO2/EG are Mn, and O. The element of Mn indicated that MnO2 oxide nanoparticles were coated on the surface of EG. It was also observed that MnO2 dispersed on the EG surface showing
Fig. 2. FSEM images of EG, MnO2/EG and EDS of MnO2/EG.
H. Jin et al. / Materials Letters 110 (2013) 69–72
71
Fig. 3. FTIR spectra of EG and MnO2/EG.
spindle-like morphologies with a diameter of 10–30 nm and a length of 30–80 nm (Fig. 2c, d). The length–diameter ratio of the nano spindle was calculated at approximately 3:1. The nano size MnO2 particles could therefore offer a larger specific surface area, providing easier access for electrolyte ions and electrons. FTIR analysis: To elucidate the adsorption mechanism, FTIR spectra of EG and MnO2/EG are presented in Fig. 3. The broad band at 3450 cm 1 and the band at 1634 cm 1 found in each sample could be attributed to the stretching vibrations of intra and intermolecular hydrogen bonded –OH and CQC, respectively. Furthermore, the bands around 2924 and 2854 cm 1 corresponded to the CH2 stretching vibrations, while the characteristic peaks appeared for CQO group at 1758 cm 1. The bands between 1461–1300 cm 1 indicated the presence of C–H bending in the –CH3 group, while the bands at 1124 were attributed to the –CO stretching for secondary alcohol. As EG was prepared by a KMnO4 oxidation process (Fig. 3), the EG showed an absorption peak at 526 cm 1, which was characteristic for Mn–O undergoing stretching vibration. The changes occurred on EG after the samples were treated by KMnO4 and MnSO4. Compared with the EG sample, the adsorption band of MnO2/EG at 1758 cm 1 and 1500–1200 cm 1 disappeared completely, indicating that one-end of MnO2 had been grafted on the surface of EG through CQO groups and the C– H bending of –CH3 groups. The bands at 570 and 526 cm 1 were also ascribed to the stretching vibration of Mn–O. The effect of adsorbent dose: The effect of EG and MnO2/EG dose on the adsorption of Cr(VI) from aqueous solutions was investigated. As shown in Fig. 4, the removal efficiency of Cr(VI) by MnO2/EG increased sharply as the sorbent dose increased from 0.1 g (53.57%) to 0.3 g (90.35%). As the adsorbent additive amount increased further, the removal rate of Cr(VI) rose slowly and then reached an almost constant value of 95.9% at 0.6 g. However, as expected, the adsorption capacities decreased with increasing adsorbent mass. When the adsorbent doses were at 0.1, 0.3 and 0.6 g EG and the MnO2/EG adsorbed amounts at equilibrium were at 0.2785, 0.1583, 0.1136 and 0.5357, 0.3011, 0.1648 mg/g, respectively. Considering the factors of adsorbed amounts and removal efficiency, the optimum amount of adsorbent dose was selected as 0.3 g. Compared with MnO2/EG, EG exhibited much lower removal efficiency and adsorbed amounts for Cr(VI). However, impregnation with MnO2 significantly enhanced the adsorption capacity of the EG toward Cr(VI). I think there are two main reasons for this phenomenon. Firstly, this improvement could be attributed to the larger surface area of MnO2/EG that provides higher micropore and mesopore volumes. Secondly, MnO2 impregnation may have
Fig. 4. The effect of adsorbent dose on the adsorption of Cr(VI) by MnO2/EG and EG. (The dotted lines and solid lines correspond to qt and Cr(VI) removal efficiency, respectively.)
also introduced more functional groups such as carboxyls and phenols to the carbon surface, which could provide more adsorption sites for Cr(VI).
4. Conclusions In this work, MnO2-modified Expanded Graphite has been prepared by the reaction between Expanded Graphite, MnSO4 solution and KMnO4 solution. The XRD, FSEM and FTIR results demonstrated that the surface of the EG flakes was successfully modified. Some nano spindle-like MnO2 (with a length of 30–80 nm and a diameter of 10–30 nm) were dispersed on the surface and interspaces of EG. The obtained material possessed a much larger surface area and more functional groups such as carboxyls and phenols, which could provide more adsorption sites for Cr(VI) and enhance the adsorbed amounts. Under the optimum parameters of the adsorption experiment (Co ¼2 mg/L, pH ¼ 5, T¼ 30 1C, t¼90 min and m¼ 0.3 g) the removal rate and the adsorbed amounts reached 90.35% and 0.3011 mg/g, respectively.
Acknowledgment The work was carried out under the financial of China (No: NSFC51102218), the Wuhan Scientific and technological project (No: 201210321099) and the Fundamental Research Funds for the Central Universities (Nos: CUG120402 and CUG120118). References [1] Wu Y, Luo H, Wang H, Wang C, Zhang J, Zhang Z. Adsorption of hexavalent chromium from aqueous solutions by graphene modified with cetyltrimethylammonium bromide. Journal of Colloid and Interface Science 2013;394: 183–91. [2] Kim J, Benjamin MM. Modeling a novel ion exchange process for arsenic and nitrate removal. Water Research 2004;38:2053–62. [3] Teychene B, Collet G, Gallard H, Croue J-P. A comparative study of boron and arsenic (III) rejection from brackish water by reverse osmosis membranes. Desalination 2013;310:109–14. [4] Zaw M, Emett MT. Arsenic removal from water using advanced oxidation processes. Toxicology Letters 2002;133:113–8. [5] Pattanayak J, Mondal K, Mathew S, Lalvani SB. A parametric evaluation of the removal of As(V) and As(III) by carbon-based adsorbents. Carbon 2000;38: 589–96. [6] Das NN, Konar J, Mohanta MK, Upadhaya AK. Synthesis, characterization and adsorptive properties of hydrotalcite-like compounds derived from titanium rich bauxite. Reaction Kinetics Mechanisms and Catalysis 2010;99:167–76.
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H. Jin et al. / Materials Letters 110 (2013) 69–72
[7] Guedidi H, Reinert L, Leveque J-M, Soneda Y, Bellakhal N, Duclaux L. The effects of the surface oxidation of activated carbon, the solution pH and the temperature on adsorption of ibuprofen. Carbon 2013;54:432–43. [8] Zhu Y, Murali S, Cai W, Li X, Suk JW, Potts JR, et al. Graphene and graphene oxide: synthesis, properties, and applications. Advanced Materials 2010;22: 3906–24. [9] Yu J, Zhao T, Zeng B. Mesoporous MnO2 as enzyme immobilization host for amperometric glucose biosensor construction. Electrochemistry Communications 2008;10:1318–21.
[10] Zhang J, Chu W, Jiang J, Zhao XS. Synthesis, characterization and capacitive performance of hydrous manganese dioxide nanostructures. Nanotechnology 2011;22:125703. [11] Jia Y, Xu J, Zhou L, Liu H, Hu Y. A simple one step approach to preparation of gamma-MnOOH multipods and beta-MnO2 nanorods. Materials Letters 2008;62:1336–8.