- Email: [email protected]
Magnetic hierarchical porous carbon sphere prepared for removal of organic pollutants in water
Materials Letters 104 (2013) 64–67
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Magnetic hierarchical porous carbon sphere prepared for removal of organic pollutants in water Chengyang Yin n, Yijun Wei, Fengwu Wang, Yonghong Chen, Xia Bao Anhui Key Laboratory of Low Temperature Co-fired Materials, Department of Chemistry and Chemical Engineering, Huainan Normal University, Huainan 232001, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 January 2013 Accepted 30 March 2013 Available online 9 April 2013
A magnetic hierarchical porous carbon sphere was synthesized by a simple, facile and inexpensive ion exchange route, in which the magnetic Fe3O4 particles are dispersed in the sample. The magnetic hierarchical porous carbon sphere was characterized by combined techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption isotherms and the magnetization curve. This magnetic hierarchical porous carbon sphere has high surface area (986 m2/g), macroscopic sphere, hierarchical porosity (micropores, mesopores and macropores), and good magnetic separability properties. High surface area of this magnetic hierarchical porous carbon sphere showed an efficient adsorption capacity (152 mg/g) for organic pollutants (methyl orange) in water and can be easily separated from water by external magnetic field. & 2013 Elsevier B.V. All rights reserved.
Keywords: Porous materials Carbon materials Magnetic properties Macroscopic sphere Organic pollutants
1. Introduction With rapid developments of economics, water resources of the world are seriously contaminated. The dyes which are deeply colored and toxic have caused increasingly environmental problems [1,2]. Carbon materials with high surface area are widely used as adsorbents for treating organic pollutants in water [3,4]. However, it is difficult to separate them from the liquid medium because of their small particle sizes. Separation of carbon materials from the liquid phase needs complex and expensive steps such as filtration or centrifugation. To solve this problem, recent researchers have paid much attention on inducing magnetic particles into carbon materials. Magnetic carbon materials can be separated from the medium by a simple magnet. There are some methods to synthesize magnetic carbon materials [5–9]. For example, Sun et al. synthesized magnetically motive porous sphere composites consisting of iron carbide, iron and graphite [5]. Yang and coworkers that reported magnetic porous carbons can be prepared by γ-ray at room temperature [9]. However, there are still some disadvantages of these materials, such as complicated synthesis process and low magnetic property. The key problem is the surface area is not high enough to increase absorption capacity because of pore clogging. Carbon spheres, especially macroscopic carbon spheres [10–12], are often applied in carbon application areas because they are easily handled and can reduce diffusion limits. Recently, Wang et al.
n
Corresponding author. Tel.: +86 554 6672637; fax: +86 554 6672650. E-mail addresses: [email protected], [email protected] (C. Yin).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.03.143
synthesized macroscopic carbon spheres with commercial resin as carbon source [12]. To the best of our knowledge, high surface area magnetic macroscopic carbon sphere has not been reported previously. Herein, we report a simple and facile ion exchange route of synthesis for magnetic hierarchical porous carbon sphere (MHCS) with hierarchical porosity from an industrial anion-exchange resin. The simple and low-cost industrial resin is employed as a carbon source and aluminosilicate precursor as hard support. The resulting MHCS has high surface area, large pore volume and strong magnetic responsiveness, which make it display excellent performance in the removal of organic pollutants in water.
2. Material and methods Synthesis of magnetic hierarchical porous carbon sphere (MHCS): 3 g of industrial anion-exchange resin D201 was mixed with 20 ml of a solution (0.2 mol/L) of the ammonium iron (III) oxalate trihydrate to obtain the resin derivatives. Then 0.06 g of NaAlO2, 8 ml of TPAOH solution (20%) and 8 ml of tetraethyl orthosilicate were mixed and stirred at 90 1C for 20 h. Then the derivatives were was filtrated, washed and dried at 110 1C in the air and carbonized in 80 ml/min N2 at 750 1C for 5 h in steps of 1 1C/min. Afterward, the derivatives were washed three times with 15% hydrofluoric acid and then rinsed with water and ethanol. After drying at 110 1C in air for 6 h, MHCSs were obtained. For comparison, a sample without NaAlO2, TPAOH and tetraethyl orthosilicate under the similar conditions was synthesized.
C. Yin et al. / Materials Letters 104 (2013) 64–67
Characterization: X-ray powder diffraction (XRD) was obtained with a Siemens D5005 diffractometer. Scanning electron microscopy (SEM) was performed on Hitachi S-4000 electron microscopes. Transmission electron microscopy (TEM) images were obtained on a JSM-3010. Nitrogen isotherms were measured at 77 K using a Micrometeritics ASAP 2010. The surface area was calculated using the Brunauer–Emmett–Teller (BET) method. The magnetization curve was measured on a Quantum Design MPMS-7 SQUID magnetometer at room temperature under a varying magnetic field. Water treatment experiments: 50 ml of methyl orange (MO) solution (0.1 g/L) was mixed with 0.1 g of MHCS. The suspension was then stirred continuously at room temperature. Analytical samples were taken from the suspension after various adsorption times. The MHCS with adsorbed MO was separated by a magnet and then immersed into 50 mL ethanol to release MO at room temperature. After almost complete desorption of MO in ethanol, the regenerated MHCS was separated by a magnet and used once more to adsorb MO. The MO concentration was determined spectrophotometrically using a model UV–vis spectrophotometer.
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3. Result and discussion Characterization of MHCS: Fig. 1a shows powder XRD pattern of MHCS. The XRD pattern of MHCS shows a broad diffraction peak at 231 assigned to amorphous carbon. The obtained material presents the characteristic peaks associated with cubic Fe3O4 which are in good agreement with JCPDS No. 19-0629. Fig. 1b shows the room temperature magnetization curve of MHCS. A magnetic hysteresis loop implies a strong magnetic response to a varying magnetic field. The saturation magnetization value of the sample is 14.7 emu/g. The magnetic separability of MHCS is tested in ethanol by placing a magnet near the bottle. The black particles are attracted toward the magnet within 15 s, confirming that the sample possesses magnetic properties. This will provide an easy way to separate MHCS from a suspension under an external magnetic field. Fig. 2a shows an optical image of MHCS; the sample presents spherical morphology with sizes of several 100 mm (diameters of 300–600 mm), which are the dimensions of the original resin.
Fig. 1. (a) XRD pattern of MHCS and (b) the room temperature magnetization curve of MHCS.
Fig. 2. (a) Optical image of MHCS, (b) SEM image of MHCS, and (c) TEM image of MHCS.
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C. Yin et al. / Materials Letters 104 (2013) 64–67
Further, from scanning electron microscopy (SEM), hierarchical pores can be clearly identified on MHCS sample (Fig. 2b), indicating that the high porosity of the original resin is well conserved. Transmission electron microscopy (TEM) image (Fig. 2c) gives a direct insight into the structure properties and distribution of Fe3O4 particles on MHCS sample. The Fe3O4 particles (black dots in TEM image) are highly dispersed on MHCS sample with 80– 120 nm diameter. TEM image also shows that MHCS samples contain hierarchical mesoporous and macropores (white in TEM image). The N2 isotherms of MHCS (Fig. 3a) exhibit a steep increase in the curve at relative pressure o0.02, which is due to the filling of the micropores [13]. The Horvath–Kawazoe (HK) analysis of the pore size distribution of MHCS shows narrow uniform micropores with a mean value of 0.82 nm (Fig. 3b). A broad hysteresis loop appears at the relative pressure of 0.40–0.99, which is in agreement with the mesoporosity and macroporosity of the sample identified using SEM and TEM. The Barrett–Joyner–Halenda (BJH) analysis of the pore size distribution of MHCS confirms the presence of hierarchical mesopores and macropores in the range of 20–120 nm (Fig. 3c). The presence of porosity in the sample may result from expanding gases such as carbon dioxide and water vapor that are formed through the interaction between the carbon and oxides in the sample at high temperatures (750 1C) [14]. The MHCS has a high BET surface area (986 m2/g) and pore volume (0.87 cm3/g), which are helpful for the adsorption of organic pollutants in water. The N2 adsorption isotherms of the sample synthesized without NaAlO2, TPAOH and tetraethyl orthosilicate (Fig. S1) show porosity, but this sample has a surface area of 293 m2/g and pore volume of 0.39 cm3/g which are lower than those of MHCS. The higher surface area of MHCS was conserved using an aluminosilicate precursor, forming a hard support to prevent the structural collapse during the carbonization. MHCS in the pollutants removal: as a model pollutant, methyl orange (MO) was chosen as an adsorbate for the adsorption experiment. When MHCS is put into the water wasted by MO after a period of time, the color of water changes from orange to colorless which shows that MO has been adsorbed by MHCS. After MHCS is separated by a magnet, clean water is obtained. From Fig. 4a, we can see that the adsorption capacity of MHCS sample is high. The reason is that MHCS has a high surface area which is the key factor of the adsorption capacity. Interestingly, comparing the adsorption capacity of MHCS with that of previous works [5,9], we find that the MHCS has higher adsorption capacity due to the
Fig. 4. (a) Adsorption curve of MO in water on MHCS and (b) recycles of MHCS for adsorption of MO in water.
higher surface area. MHCS with adsorbed MO was transferred into ethanol to release MO. The MHCS was easily regenerated by desorption of MO in ethanol and separated by a magnet. After five cycles (Fig. 4b), the MHCS still shows almost the same adsorption capacity for the MO pollutants. The regenerated MHCS also was characterized by the magnetization curve (Fig. S2) and TEM (Fig. S3). The regenerated MHCS was still magnetic and had as high saturation magnetization (Fig. S2) as that of the MHCS. Fig S3 shows that the Fe3O4 particles were highly dispersed on regenerated MHCS. The Fe3O4 particles in MHCS did not fall off from the MHCS sample after five adsorption cycles.
4. Conclusions In summary, we synthesize a magnetic hierarchical porous carbon sphere by a simple and inexpensive method. This material has high surface area, hierarchical porous, macroscopic sphere and good magnetic separability properties. It shows an efficient adsorption capacity for organic pollutants in water and can be easily separated from the water by a simple magnetic process. This material could potentially be used in industrial applications.
Acknowledgments
Fig. 3. (a) Nitrogen adsorption isotherm, (b) HK pore size distribution and (c) BJH pore size distribution of MHCS.
The authors thank the Natural Science Foundation of the Education Office of Anhui Province (KJ2011B158), Youth Foundation of Huainan Normal University (2010QNL07) and Dr. Scientific Research Foundation of Huainan Normal University for financial support. We thank the anonymous reviewers for their invaluable comments.
C. Yin et al. / Materials Letters 104 (2013) 64–67
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.03.143.
References [1] Epstein SS, Joshi S, Andrea J, Mantel N, Sawick E, Stanley T, et al. Carcinogenicity of organic particulate pollutants in urban air after administration of trace quantities to neonatal mice. Nature 1966;212:1305–7. [2] Lewis DL, Garrison AW, Wommack KE, Whittemore A, Steudler P, Melillo J. Influence of environmental changes on degradation of chiral pollutants in soils. Nature 1999;401:898–901. [3] Lee J, Kim J, Hyeon T. Recent progress in the synthesis of porous carbon materials. Adv Mater 2006;18:2073–94. [4] Zhao N, Wu S, He C, Shi C, Liu E, Du X, et al. Hierarchical porous carbon with graphitic structure synthesized by a water soluble template method. Mater Lett 2012;87:77–9. [5] Sun ZH, Wang LF, Liu PP, Wang SC, Sun B, Jiang DZ, et al. Magnetically motive porous sphere composite and its excellent properties for the removal of pollutants in water by adsorption and desorption cycles. Adv Mater 2006;18:1968–71.
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[6] Liu J, Qiao SZ, Hu QH, Lu GQM. Magnetic nanocomposites with mesoporous structures: synthesis and applications. Small 2011;7:425–43. [7] Zhang YX, Xu SC, Luo YY, Pan SS, Ding HL, Li GH. Synthesis of mesoporous carbon capsules encapsulated with magnetite nanoparticles and their application in wastewater treatment. J Mater Chem 2011;21:3664–71. [8] Wu ZX, Li W, Webley PA, Zhao DY. General and controllable synthesis of novel mesoporous magnetic iron oxide at carbon encapsulates for efficient arsenic removal. Adv Mater 2012;24:485–91. [9] Yang S, Wang Y, Nie C, Liu H, Liu H. A facile approach to superparamagnetic porous carbons and its high capability for the removal of pollutants in water. Mater Lett 2013;92:14–6. [10] Deshmukh AA, Mhlanga SD, Coville NJ. Carbon spheres. Mater Sci Eng R 2010;70:1–28. [11] Tosheva L, Parmentier J, Saadallah S, Vix-Guterl C, Valtchev V, Patarin J. SiC macroscopic beads from ion-exchange resin templates. J Am Chem Soc 2004;126:13624–5. [12] Wang L, Delgado JJ, Frank B, Zhang Z, Shan Z, Su DS, et al. Resin-derived hierarchical porous carbon spheres with high catalytic performance in the oxidative dehydrogenation of ethylbenzene. ChemSusChem 2012;5:687–93. [13] Sing KSW, Everett DH, Raw Haul, Moscou L, Pierotti RA, Rouquerol J, et al. Reporting physisorption data for gas/solid systems. Pure Appl Chem 1985;57:603–19. [14] Hummelshøj JS, Sørensen RZ, Kustova MY, Johannessen T, Nørskov JK, Christensen CH. Generation of nanopores during desorption of NH3 from Mg (NH3)6Cl2. J Am Chem Soc 2006;128:16–7.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Magnetic hierarchical porous carbon sphere prepared for removal of organic pollutants in water Chengyang Yin n, Yijun Wei, Fengwu Wang, Yonghong Chen, Xia Bao Anhui Key Laboratory of Low Temperature Co-fired Materials, Department of Chemistry and Chemical Engineering, Huainan Normal University, Huainan 232001, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 4 January 2013 Accepted 30 March 2013 Available online 9 April 2013
A magnetic hierarchical porous carbon sphere was synthesized by a simple, facile and inexpensive ion exchange route, in which the magnetic Fe3O4 particles are dispersed in the sample. The magnetic hierarchical porous carbon sphere was characterized by combined techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption desorption isotherms and the magnetization curve. This magnetic hierarchical porous carbon sphere has high surface area (986 m2/g), macroscopic sphere, hierarchical porosity (micropores, mesopores and macropores), and good magnetic separability properties. High surface area of this magnetic hierarchical porous carbon sphere showed an efficient adsorption capacity (152 mg/g) for organic pollutants (methyl orange) in water and can be easily separated from water by external magnetic field. & 2013 Elsevier B.V. All rights reserved.
Keywords: Porous materials Carbon materials Magnetic properties Macroscopic sphere Organic pollutants
1. Introduction With rapid developments of economics, water resources of the world are seriously contaminated. The dyes which are deeply colored and toxic have caused increasingly environmental problems [1,2]. Carbon materials with high surface area are widely used as adsorbents for treating organic pollutants in water [3,4]. However, it is difficult to separate them from the liquid medium because of their small particle sizes. Separation of carbon materials from the liquid phase needs complex and expensive steps such as filtration or centrifugation. To solve this problem, recent researchers have paid much attention on inducing magnetic particles into carbon materials. Magnetic carbon materials can be separated from the medium by a simple magnet. There are some methods to synthesize magnetic carbon materials [5–9]. For example, Sun et al. synthesized magnetically motive porous sphere composites consisting of iron carbide, iron and graphite [5]. Yang and coworkers that reported magnetic porous carbons can be prepared by γ-ray at room temperature [9]. However, there are still some disadvantages of these materials, such as complicated synthesis process and low magnetic property. The key problem is the surface area is not high enough to increase absorption capacity because of pore clogging. Carbon spheres, especially macroscopic carbon spheres [10–12], are often applied in carbon application areas because they are easily handled and can reduce diffusion limits. Recently, Wang et al.
n
Corresponding author. Tel.: +86 554 6672637; fax: +86 554 6672650. E-mail addresses: [email protected], [email protected] (C. Yin).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.03.143
synthesized macroscopic carbon spheres with commercial resin as carbon source [12]. To the best of our knowledge, high surface area magnetic macroscopic carbon sphere has not been reported previously. Herein, we report a simple and facile ion exchange route of synthesis for magnetic hierarchical porous carbon sphere (MHCS) with hierarchical porosity from an industrial anion-exchange resin. The simple and low-cost industrial resin is employed as a carbon source and aluminosilicate precursor as hard support. The resulting MHCS has high surface area, large pore volume and strong magnetic responsiveness, which make it display excellent performance in the removal of organic pollutants in water.
2. Material and methods Synthesis of magnetic hierarchical porous carbon sphere (MHCS): 3 g of industrial anion-exchange resin D201 was mixed with 20 ml of a solution (0.2 mol/L) of the ammonium iron (III) oxalate trihydrate to obtain the resin derivatives. Then 0.06 g of NaAlO2, 8 ml of TPAOH solution (20%) and 8 ml of tetraethyl orthosilicate were mixed and stirred at 90 1C for 20 h. Then the derivatives were was filtrated, washed and dried at 110 1C in the air and carbonized in 80 ml/min N2 at 750 1C for 5 h in steps of 1 1C/min. Afterward, the derivatives were washed three times with 15% hydrofluoric acid and then rinsed with water and ethanol. After drying at 110 1C in air for 6 h, MHCSs were obtained. For comparison, a sample without NaAlO2, TPAOH and tetraethyl orthosilicate under the similar conditions was synthesized.
C. Yin et al. / Materials Letters 104 (2013) 64–67
Characterization: X-ray powder diffraction (XRD) was obtained with a Siemens D5005 diffractometer. Scanning electron microscopy (SEM) was performed on Hitachi S-4000 electron microscopes. Transmission electron microscopy (TEM) images were obtained on a JSM-3010. Nitrogen isotherms were measured at 77 K using a Micrometeritics ASAP 2010. The surface area was calculated using the Brunauer–Emmett–Teller (BET) method. The magnetization curve was measured on a Quantum Design MPMS-7 SQUID magnetometer at room temperature under a varying magnetic field. Water treatment experiments: 50 ml of methyl orange (MO) solution (0.1 g/L) was mixed with 0.1 g of MHCS. The suspension was then stirred continuously at room temperature. Analytical samples were taken from the suspension after various adsorption times. The MHCS with adsorbed MO was separated by a magnet and then immersed into 50 mL ethanol to release MO at room temperature. After almost complete desorption of MO in ethanol, the regenerated MHCS was separated by a magnet and used once more to adsorb MO. The MO concentration was determined spectrophotometrically using a model UV–vis spectrophotometer.
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3. Result and discussion Characterization of MHCS: Fig. 1a shows powder XRD pattern of MHCS. The XRD pattern of MHCS shows a broad diffraction peak at 231 assigned to amorphous carbon. The obtained material presents the characteristic peaks associated with cubic Fe3O4 which are in good agreement with JCPDS No. 19-0629. Fig. 1b shows the room temperature magnetization curve of MHCS. A magnetic hysteresis loop implies a strong magnetic response to a varying magnetic field. The saturation magnetization value of the sample is 14.7 emu/g. The magnetic separability of MHCS is tested in ethanol by placing a magnet near the bottle. The black particles are attracted toward the magnet within 15 s, confirming that the sample possesses magnetic properties. This will provide an easy way to separate MHCS from a suspension under an external magnetic field. Fig. 2a shows an optical image of MHCS; the sample presents spherical morphology with sizes of several 100 mm (diameters of 300–600 mm), which are the dimensions of the original resin.
Fig. 1. (a) XRD pattern of MHCS and (b) the room temperature magnetization curve of MHCS.
Fig. 2. (a) Optical image of MHCS, (b) SEM image of MHCS, and (c) TEM image of MHCS.
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C. Yin et al. / Materials Letters 104 (2013) 64–67
Further, from scanning electron microscopy (SEM), hierarchical pores can be clearly identified on MHCS sample (Fig. 2b), indicating that the high porosity of the original resin is well conserved. Transmission electron microscopy (TEM) image (Fig. 2c) gives a direct insight into the structure properties and distribution of Fe3O4 particles on MHCS sample. The Fe3O4 particles (black dots in TEM image) are highly dispersed on MHCS sample with 80– 120 nm diameter. TEM image also shows that MHCS samples contain hierarchical mesoporous and macropores (white in TEM image). The N2 isotherms of MHCS (Fig. 3a) exhibit a steep increase in the curve at relative pressure o0.02, which is due to the filling of the micropores [13]. The Horvath–Kawazoe (HK) analysis of the pore size distribution of MHCS shows narrow uniform micropores with a mean value of 0.82 nm (Fig. 3b). A broad hysteresis loop appears at the relative pressure of 0.40–0.99, which is in agreement with the mesoporosity and macroporosity of the sample identified using SEM and TEM. The Barrett–Joyner–Halenda (BJH) analysis of the pore size distribution of MHCS confirms the presence of hierarchical mesopores and macropores in the range of 20–120 nm (Fig. 3c). The presence of porosity in the sample may result from expanding gases such as carbon dioxide and water vapor that are formed through the interaction between the carbon and oxides in the sample at high temperatures (750 1C) [14]. The MHCS has a high BET surface area (986 m2/g) and pore volume (0.87 cm3/g), which are helpful for the adsorption of organic pollutants in water. The N2 adsorption isotherms of the sample synthesized without NaAlO2, TPAOH and tetraethyl orthosilicate (Fig. S1) show porosity, but this sample has a surface area of 293 m2/g and pore volume of 0.39 cm3/g which are lower than those of MHCS. The higher surface area of MHCS was conserved using an aluminosilicate precursor, forming a hard support to prevent the structural collapse during the carbonization. MHCS in the pollutants removal: as a model pollutant, methyl orange (MO) was chosen as an adsorbate for the adsorption experiment. When MHCS is put into the water wasted by MO after a period of time, the color of water changes from orange to colorless which shows that MO has been adsorbed by MHCS. After MHCS is separated by a magnet, clean water is obtained. From Fig. 4a, we can see that the adsorption capacity of MHCS sample is high. The reason is that MHCS has a high surface area which is the key factor of the adsorption capacity. Interestingly, comparing the adsorption capacity of MHCS with that of previous works [5,9], we find that the MHCS has higher adsorption capacity due to the
Fig. 4. (a) Adsorption curve of MO in water on MHCS and (b) recycles of MHCS for adsorption of MO in water.
higher surface area. MHCS with adsorbed MO was transferred into ethanol to release MO. The MHCS was easily regenerated by desorption of MO in ethanol and separated by a magnet. After five cycles (Fig. 4b), the MHCS still shows almost the same adsorption capacity for the MO pollutants. The regenerated MHCS also was characterized by the magnetization curve (Fig. S2) and TEM (Fig. S3). The regenerated MHCS was still magnetic and had as high saturation magnetization (Fig. S2) as that of the MHCS. Fig S3 shows that the Fe3O4 particles were highly dispersed on regenerated MHCS. The Fe3O4 particles in MHCS did not fall off from the MHCS sample after five adsorption cycles.
4. Conclusions In summary, we synthesize a magnetic hierarchical porous carbon sphere by a simple and inexpensive method. This material has high surface area, hierarchical porous, macroscopic sphere and good magnetic separability properties. It shows an efficient adsorption capacity for organic pollutants in water and can be easily separated from the water by a simple magnetic process. This material could potentially be used in industrial applications.
Acknowledgments
Fig. 3. (a) Nitrogen adsorption isotherm, (b) HK pore size distribution and (c) BJH pore size distribution of MHCS.
The authors thank the Natural Science Foundation of the Education Office of Anhui Province (KJ2011B158), Youth Foundation of Huainan Normal University (2010QNL07) and Dr. Scientific Research Foundation of Huainan Normal University for financial support. We thank the anonymous reviewers for their invaluable comments.
C. Yin et al. / Materials Letters 104 (2013) 64–67
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.03.143.
References [1] Epstein SS, Joshi S, Andrea J, Mantel N, Sawick E, Stanley T, et al. Carcinogenicity of organic particulate pollutants in urban air after administration of trace quantities to neonatal mice. Nature 1966;212:1305–7. [2] Lewis DL, Garrison AW, Wommack KE, Whittemore A, Steudler P, Melillo J. Influence of environmental changes on degradation of chiral pollutants in soils. Nature 1999;401:898–901. [3] Lee J, Kim J, Hyeon T. Recent progress in the synthesis of porous carbon materials. Adv Mater 2006;18:2073–94. [4] Zhao N, Wu S, He C, Shi C, Liu E, Du X, et al. Hierarchical porous carbon with graphitic structure synthesized by a water soluble template method. Mater Lett 2012;87:77–9. [5] Sun ZH, Wang LF, Liu PP, Wang SC, Sun B, Jiang DZ, et al. Magnetically motive porous sphere composite and its excellent properties for the removal of pollutants in water by adsorption and desorption cycles. Adv Mater 2006;18:1968–71.
67
[6] Liu J, Qiao SZ, Hu QH, Lu GQM. Magnetic nanocomposites with mesoporous structures: synthesis and applications. Small 2011;7:425–43. [7] Zhang YX, Xu SC, Luo YY, Pan SS, Ding HL, Li GH. Synthesis of mesoporous carbon capsules encapsulated with magnetite nanoparticles and their application in wastewater treatment. J Mater Chem 2011;21:3664–71. [8] Wu ZX, Li W, Webley PA, Zhao DY. General and controllable synthesis of novel mesoporous magnetic iron oxide at carbon encapsulates for efficient arsenic removal. Adv Mater 2012;24:485–91. [9] Yang S, Wang Y, Nie C, Liu H, Liu H. A facile approach to superparamagnetic porous carbons and its high capability for the removal of pollutants in water. Mater Lett 2013;92:14–6. [10] Deshmukh AA, Mhlanga SD, Coville NJ. Carbon spheres. Mater Sci Eng R 2010;70:1–28. [11] Tosheva L, Parmentier J, Saadallah S, Vix-Guterl C, Valtchev V, Patarin J. SiC macroscopic beads from ion-exchange resin templates. J Am Chem Soc 2004;126:13624–5. [12] Wang L, Delgado JJ, Frank B, Zhang Z, Shan Z, Su DS, et al. Resin-derived hierarchical porous carbon spheres with high catalytic performance in the oxidative dehydrogenation of ethylbenzene. ChemSusChem 2012;5:687–93. [13] Sing KSW, Everett DH, Raw Haul, Moscou L, Pierotti RA, Rouquerol J, et al. Reporting physisorption data for gas/solid systems. Pure Appl Chem 1985;57:603–19. [14] Hummelshøj JS, Sørensen RZ, Kustova MY, Johannessen T, Nørskov JK, Christensen CH. Generation of nanopores during desorption of NH3 from Mg (NH3)6Cl2. J Am Chem Soc 2006;128:16–7.