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Hollow porous carbon sphere prepared by a facile activation method and its rapid phenol removal
Materials Letters 126 (2014) 13–16
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hollow porous carbon sphere prepared by a facile activation method and its rapid phenol removal Binbin Chang, Weiwei Shi, Daxiang Guan, Yiliang Wang, Baocheng Zhou, Xiaoping Dong n Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 928 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018, China
art ic l e i nf o
a b s t r a c t
Article history: Received 21 October 2013 Accepted 29 March 2014 Available online 12 April 2014
Hollow porous carbon spheres (HPCS) were prepared by a facile activation strategy. During the one-step activation treatment we could obtain the hollow and porous structures simultaneously. The HPCS materials possessed good monodispersity, uniform hollow morphology and very high surface area. Besides, these materials also exhibited excellent adsorption ability for the removal of phenol from the waste water. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Porous materials Hollow sphere Adsorption
1. Introduction Currently, nanotechnology depends importantly on the ability to prepare novel nanomaterials possessing unique structural and functional features. In this context, monodisperse hollow nanospheres with a controlled diameter have attracted much research and industrial interest. In the past decades, many hollow sphere materials, such as hollow sphere of silica [1], carbon [2], metal oxide [3], have been successfully synthesized using various methods, for instance template synthesis [4], self-assembly [5] and so on. The template method is undoubtedly one of the most used and well-developed route for fabrication of hollow spheres. In general, spherical particles are used as scarifying templates, on the surface of which a layer of the desired chemical matter is coated or deposited, followed by a removal of the spherical particles to leave behind a hollow structure. Among these hollow nanosphere materials, hollow carbon sphere materials, especially HPCS materials, have received considerable attention recently for applications in energy storage, catalysis and water treatment, owing to their unique structure and functional behavior, such as high surface area, low density and large controllable inner pore volume. Various approaches have been developed for preparing HPCS materials. The first major class of the synthesis methods is the hard template method, which has been demonstrated to produce monodisperse HPCS with controllable morphology and inner pore structure. For example, Arnal et al. reported the fabrication of HPCS materials with a template of spherical SiO2@ZrO2 core–shell structure [6]. In spite of the n
Corresponding author. Tel./fax: þ 86 571 86843228. E-mail address: [email protected] (X. Dong).
http://dx.doi.org/10.1016/j.matlet.2014.03.177 0167-577X/& 2014 Elsevier B.V. All rights reserved.
success of the hard template method in synthesis of HPCS materials, this route is a typical multiple step process, as it inevitably requires the fabrication of core–shell templates and the subsequent removal of these templates, which often involves the employment noxious chemical etching, such as hydrofluoric acid and concentrated alkali. Therefore, the soft template route is adopted to simplify the synthesis process of HPCS. Yang et al. successfully produced hollow porous carbon nanoparticles using F127 as a soft temple [7]. However, this method usually uses block copolymers and surfactants as the soft template, and these raw materials are costly, which immensely increase the cost of preparation. Furthermore, the soft template method is a timeconsuming process and it is difficult to precisely control the shell thickness, sphere diameter and overall morphology of the resultant HPCS materials [7]. In this paper, we investigate the use of inexpensive renewable carbohydrate precursor in combination with metal oxide template to produce HPCS via a simple chemical activation of ZnCl2.
2. Experimental section Materials synthesis: The dispersible Fe3O4 nanoparticles and Fe3O4@C microspheres were synthesized according to the method reported previously [8]. Subsequently, the dried Fe3O4@C materials were impregnated in ZnCl2 solution (the mass ratio of ZnCl2/ Fe3O4@C ¼4:1) for 6 h, and dried at 110 1C for 12 h and then was activated in a N2 atmosphere at 400 1C for 1 h. After cooling down, the activated samples were thoroughly washed with distilled water and HCl solution (0.5 M). Finally, the materials were dried under vacuum at 80 1C for 10 h to obtain HPCS.
14
B. Chang et al. / Materials Letters 126 (2014) 13–16
Characterization: The X-ray diffraction (XRD) patterns of powder samples were taken by a Bruker D8 Advance diffractometer using Cu Kα radiation (λ ¼0.15418 nm) as an X-ray source. N2 adsorption–desorption isotherms were carried out at 196 1C using a micromeritics ASAP 2020 analyzer. The specific surface area (SBET) was evaluated using the Brunauer–Emmett–Teller (BET) method. The pore size distributions were calculated according to the Density Functional Theory (DFT) method. Fourier transform infrared spectroscopy (FTIR) spectra of a sample in KBr pellet were recorded on a Nicolet Avatar 370 spectrometer. The morphology was observed from a JEOL JEM–2100 transmission electron microscope (TEM) with an accelerating voltage of 200 KV and a scanning electron microscope (SEM, Hitachi S-4800). Adsorption studies: The adsorption performance of as-prepared materials was evaluated by removing phenol. Typically, 20 mg of adsorbent was immersed into a 50 mL of certain phenol concentration under violent stirring at room temperature. The UV–vis spectra (Shimadzu, UV-2450PC) were used to estimate the adsorption process at a certain time interval.
3. Results and discussion XRD patterns of Fe3O4, Fe3O4@C and HPCS are shown in Fig. 1 to demonstrate the evolution of the material structure. The characteristic diffraction peaks of Fe3O4 are present in Fe3O4 and Fe3O4@C samples, which can be assigned to (220), (311), (400), (511) and (440) planes of a pure cubic Fe3O4 phase [9]. In comparison with pure Fe3O4 sample, an additional broad diffraction peak at 2θ ¼20 301 appears in Fe3O4@C sample. This weak diffraction of amorphous carbon verifies the successful coating of carbon layer onto the magnetic core. However, after activation with ZnCl2, the diffraction peaks of Fe3O4 disappear and only the diffraction peak of amorphous carbon is reserved in HPCS sample, which implies that the Fe3O4 magnetic core is dissolved in the process of activation and the hollow structure is subsequently formed. FTIR spectra also demonstrate the removal of Fe3O4 and the changing of surface functional groups after activation (Fig. 1b). Fe3O4 sample presents the characteristic bands of Fe–O appeared at 580 and 630 cm 1 [10]. After being coated with carbon shell, two additional adsorption bands at 1620 and 1710 cm 1 are found in Fe3O4@C sample, which are ascribed to CQC and CQO stretching vibrations [11], respectively, verifying the formation of carbon shell. The bands centered at 1000 1300 cm 1 are related to the C–O stretching vibration and –OH bending vibration. After activation, the characteristic bands of Fe–O disappear, and these evidences identify that the Fe3O4 magnetic core is indeed dissolved in the process of activation. Meanwhile, the absorption peaks of C–O and C–OH become illegible and even the characteristic absorption band of CQO at 1710 cm 1 disappears, which
should be due to the chemical activation with ZnCl2 by the release of H2O molecule. To reveal the morphology and structure of HPCS, SEM and TEM images of HPCS are shown in Fig. 2. As shown in Fig. 2a–b, these spheres are monodisperse and nearly uniform in dimension with particle diameters of ca. 300 nm. At high magnification of SEM images (Fig. 2b), some of carbon spheres are partially broken, which clearly shows the hollow sphere morphology. In the TEM images of HPCS (Fig. 2c and d), a hollow sphere structure is apparently displayed. The thickness of carbon shell is ca. 20 nm, and the size of the hollow carbon sphere is about 300 nm, which is identical with the result of SEM. To investigate the porosity of HPCS, the nitrogen sorption isotherm and pore size distribution of HPCS are shown in Fig. 3. The N2 adsorption–desorption isotherm of HPCS shows typical type IV curves with a hysteresis loop at relative pressure from 0.4 to 0.5, indicating the existence of mesopore. Very interestingly, the HPCS material possesses an extremely high surface area of 2012.3 m2 g 1 and a total pore volume of 1.34 cm3 g 1, which are much higher than those of other hollow porous carbon materials prepared by the hard template and the soft template routes [12,13]. In addition, as shown in Fig. 3b, the pore size distribution of HPCS calculated by the DFT method clearly suggests this HPCS material has a narrow distribution of pore size centered at 2.73–3.43 nm, which is comparable with ordered mesoporous carbons. The pore size distribution of HPCS shown in Fig. 3c demonstrates the presence of macropore, which should be related to the hollow sphere structure. The HPCS material possesses high surface area, large pore volume and suitable pore size, which makes it to be a good adsorbent for removal phenol from aqueous solution. Adsorption isotherms at room temperature under neutral conditions are shown in Fig. 4. Adsorption isotherms show that the HPCS has an impressive adsorption capacity, which is overwhelmingly higher than those of traditional adsorbents, such as CMK-3 and AC. The Langmuir isotherm model and Freundlich isotherm model are used to describe the adsorption behavior of phenol on HPCS. The adsorption isotherm data can be well-fitted by the Langmuir model (Fig. S1, Supporting information), indicating a monolayer adsorption behavior with excellently high adsorption capacity (Table S1). The calculated maximum adsorption capacity of phenol on HPCS is up to 277.1 mg g 1 which is much larger than 194.9 and 95.2 mg g 1 of the compared sample CMK-3 and AC, respectively, as well as larger than those of reported phenolic sorbents [14,15].
4. Conclusion In summary, a facile synthesis strategy has been successfully developed for preparing HPCS materials by one-step activation treatment to obtain hollow and porous structure simultaneously. The HPCS materials possess very high surface area, large pore
Fig. 1. The XRD patterns (a) and FTIR spectra of (b) Fe3O4, Fe3O4@C and HPCS materials.
B. Chang et al. / Materials Letters 126 (2014) 13–16
15
Fig. 2. SEM (a and b) and TEM (c and d) images of HPCS material.
Fig. 3. N2 adsorption–desorption isotherm (a) and the pore size distribution (b and c) of HPCS material.
volume and narrow pore size distribution, and meanwhile the batch adsorption tests indicate that HPCS has an excellent adsorption capacity for phenol, and its equilibrated adsorption amount is much higher than those of the conventional adsorbents. Consequently, the HPCS material can be used as a good adsorbent to remove phenol from waste water. Furthermore, the synthesis method is quite facile and economical for preparing other hollow porous carbon materials. These materials will find many applications in sorption, catalysis and energy storage.
Acknowledgments
Fig. 4. Adsorption isotherm curve of phenol over different adsorbents material at room temperature.
The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (21001093), 521 talent project of ZSTU, the project-sponsored by the Scientific
16
B. Chang et al. / Materials Letters 126 (2014) 13–16
Research Foundation (SRF) for the Returned Overseas Chinese Scholars (ROCS), State Education Ministry (SEM), Zhejiang Provincial Natural Science Foundation of China (No. LQ13B020006).
[3] [4] [5] [6] [7]
Appendix A. Supporting information
[8]
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2014.03. 177.
[9] [10] [11] [12] [13]
References
[14]
[1] Chen M, Wu L, Zhou S, You B. Adv Mater 2006;18:801–6. [2] Wang Q, Yan J, Wang YB, Ning GD, Fang ZJ, Wei T, et al. 2013;52:209–18.
[15] Carbon
Titirici MM, Antonietti M, Thomas A. Chem Mater 2006;18:3808–12. Yang S, Feng X, Zhi L, Cao Q, Maier J, Mullen K. Adv Mater 2010;22:838–42. Liu B, Zeng HC. Small 2005;1:566–71. Arnal PM, Schuth F, Kleitz F. Chem Commun 2006:1203–5. Yang ZC, Zhang Y, Kong JH, Wong SY, Li X, Wang J. Chem Mater 2013;25:704–10. Chang BB, Tian YL, Shi WW, Liu JY, Xi FN, Dong XP. RSC Adv 2013;3:20999–1006. Shuter B, Li X, Wang J. Adv Funct Mater 2010;20:722–31. Chen FH, Gao Q, Ni JZ. Nanotechnology 2008;19:1–9. Chang BB, Fu J, Tian YL, Dong XP. J. Phys Chem C 2013;117:6252–8. Yang ZC, Tang CH, Gong H, Li X, Wang J. J. Power Sources 2013;240:713–20. Tian WQ, Wu XY, Wang KX, Jiang YM, Wang JF, Chen JS. RSC Adv 2013;3:10823–7. Mohanty K, Jha M, Meikap BC, Biswas MN. Ind Eng Chem Res 2005;44:4128–38. Senturk HB, Ozdes D, Gundogdu A, Duran C, Soylak M. J. Hazard Mater 2009;172:353–62.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hollow porous carbon sphere prepared by a facile activation method and its rapid phenol removal Binbin Chang, Weiwei Shi, Daxiang Guan, Yiliang Wang, Baocheng Zhou, Xiaoping Dong n Department of Chemistry, School of Sciences, Zhejiang Sci-Tech University, 928 Second Avenue, Xiasha Higher Education Zone, Hangzhou 310018, China
art ic l e i nf o
a b s t r a c t
Article history: Received 21 October 2013 Accepted 29 March 2014 Available online 12 April 2014
Hollow porous carbon spheres (HPCS) were prepared by a facile activation strategy. During the one-step activation treatment we could obtain the hollow and porous structures simultaneously. The HPCS materials possessed good monodispersity, uniform hollow morphology and very high surface area. Besides, these materials also exhibited excellent adsorption ability for the removal of phenol from the waste water. & 2014 Elsevier B.V. All rights reserved.
Keywords: Carbon materials Porous materials Hollow sphere Adsorption
1. Introduction Currently, nanotechnology depends importantly on the ability to prepare novel nanomaterials possessing unique structural and functional features. In this context, monodisperse hollow nanospheres with a controlled diameter have attracted much research and industrial interest. In the past decades, many hollow sphere materials, such as hollow sphere of silica [1], carbon [2], metal oxide [3], have been successfully synthesized using various methods, for instance template synthesis [4], self-assembly [5] and so on. The template method is undoubtedly one of the most used and well-developed route for fabrication of hollow spheres. In general, spherical particles are used as scarifying templates, on the surface of which a layer of the desired chemical matter is coated or deposited, followed by a removal of the spherical particles to leave behind a hollow structure. Among these hollow nanosphere materials, hollow carbon sphere materials, especially HPCS materials, have received considerable attention recently for applications in energy storage, catalysis and water treatment, owing to their unique structure and functional behavior, such as high surface area, low density and large controllable inner pore volume. Various approaches have been developed for preparing HPCS materials. The first major class of the synthesis methods is the hard template method, which has been demonstrated to produce monodisperse HPCS with controllable morphology and inner pore structure. For example, Arnal et al. reported the fabrication of HPCS materials with a template of spherical SiO2@ZrO2 core–shell structure [6]. In spite of the n
Corresponding author. Tel./fax: þ 86 571 86843228. E-mail address: [email protected] (X. Dong).
http://dx.doi.org/10.1016/j.matlet.2014.03.177 0167-577X/& 2014 Elsevier B.V. All rights reserved.
success of the hard template method in synthesis of HPCS materials, this route is a typical multiple step process, as it inevitably requires the fabrication of core–shell templates and the subsequent removal of these templates, which often involves the employment noxious chemical etching, such as hydrofluoric acid and concentrated alkali. Therefore, the soft template route is adopted to simplify the synthesis process of HPCS. Yang et al. successfully produced hollow porous carbon nanoparticles using F127 as a soft temple [7]. However, this method usually uses block copolymers and surfactants as the soft template, and these raw materials are costly, which immensely increase the cost of preparation. Furthermore, the soft template method is a timeconsuming process and it is difficult to precisely control the shell thickness, sphere diameter and overall morphology of the resultant HPCS materials [7]. In this paper, we investigate the use of inexpensive renewable carbohydrate precursor in combination with metal oxide template to produce HPCS via a simple chemical activation of ZnCl2.
2. Experimental section Materials synthesis: The dispersible Fe3O4 nanoparticles and Fe3O4@C microspheres were synthesized according to the method reported previously [8]. Subsequently, the dried Fe3O4@C materials were impregnated in ZnCl2 solution (the mass ratio of ZnCl2/ Fe3O4@C ¼4:1) for 6 h, and dried at 110 1C for 12 h and then was activated in a N2 atmosphere at 400 1C for 1 h. After cooling down, the activated samples were thoroughly washed with distilled water and HCl solution (0.5 M). Finally, the materials were dried under vacuum at 80 1C for 10 h to obtain HPCS.
14
B. Chang et al. / Materials Letters 126 (2014) 13–16
Characterization: The X-ray diffraction (XRD) patterns of powder samples were taken by a Bruker D8 Advance diffractometer using Cu Kα radiation (λ ¼0.15418 nm) as an X-ray source. N2 adsorption–desorption isotherms were carried out at 196 1C using a micromeritics ASAP 2020 analyzer. The specific surface area (SBET) was evaluated using the Brunauer–Emmett–Teller (BET) method. The pore size distributions were calculated according to the Density Functional Theory (DFT) method. Fourier transform infrared spectroscopy (FTIR) spectra of a sample in KBr pellet were recorded on a Nicolet Avatar 370 spectrometer. The morphology was observed from a JEOL JEM–2100 transmission electron microscope (TEM) with an accelerating voltage of 200 KV and a scanning electron microscope (SEM, Hitachi S-4800). Adsorption studies: The adsorption performance of as-prepared materials was evaluated by removing phenol. Typically, 20 mg of adsorbent was immersed into a 50 mL of certain phenol concentration under violent stirring at room temperature. The UV–vis spectra (Shimadzu, UV-2450PC) were used to estimate the adsorption process at a certain time interval.
3. Results and discussion XRD patterns of Fe3O4, Fe3O4@C and HPCS are shown in Fig. 1 to demonstrate the evolution of the material structure. The characteristic diffraction peaks of Fe3O4 are present in Fe3O4 and Fe3O4@C samples, which can be assigned to (220), (311), (400), (511) and (440) planes of a pure cubic Fe3O4 phase [9]. In comparison with pure Fe3O4 sample, an additional broad diffraction peak at 2θ ¼20 301 appears in Fe3O4@C sample. This weak diffraction of amorphous carbon verifies the successful coating of carbon layer onto the magnetic core. However, after activation with ZnCl2, the diffraction peaks of Fe3O4 disappear and only the diffraction peak of amorphous carbon is reserved in HPCS sample, which implies that the Fe3O4 magnetic core is dissolved in the process of activation and the hollow structure is subsequently formed. FTIR spectra also demonstrate the removal of Fe3O4 and the changing of surface functional groups after activation (Fig. 1b). Fe3O4 sample presents the characteristic bands of Fe–O appeared at 580 and 630 cm 1 [10]. After being coated with carbon shell, two additional adsorption bands at 1620 and 1710 cm 1 are found in Fe3O4@C sample, which are ascribed to CQC and CQO stretching vibrations [11], respectively, verifying the formation of carbon shell. The bands centered at 1000 1300 cm 1 are related to the C–O stretching vibration and –OH bending vibration. After activation, the characteristic bands of Fe–O disappear, and these evidences identify that the Fe3O4 magnetic core is indeed dissolved in the process of activation. Meanwhile, the absorption peaks of C–O and C–OH become illegible and even the characteristic absorption band of CQO at 1710 cm 1 disappears, which
should be due to the chemical activation with ZnCl2 by the release of H2O molecule. To reveal the morphology and structure of HPCS, SEM and TEM images of HPCS are shown in Fig. 2. As shown in Fig. 2a–b, these spheres are monodisperse and nearly uniform in dimension with particle diameters of ca. 300 nm. At high magnification of SEM images (Fig. 2b), some of carbon spheres are partially broken, which clearly shows the hollow sphere morphology. In the TEM images of HPCS (Fig. 2c and d), a hollow sphere structure is apparently displayed. The thickness of carbon shell is ca. 20 nm, and the size of the hollow carbon sphere is about 300 nm, which is identical with the result of SEM. To investigate the porosity of HPCS, the nitrogen sorption isotherm and pore size distribution of HPCS are shown in Fig. 3. The N2 adsorption–desorption isotherm of HPCS shows typical type IV curves with a hysteresis loop at relative pressure from 0.4 to 0.5, indicating the existence of mesopore. Very interestingly, the HPCS material possesses an extremely high surface area of 2012.3 m2 g 1 and a total pore volume of 1.34 cm3 g 1, which are much higher than those of other hollow porous carbon materials prepared by the hard template and the soft template routes [12,13]. In addition, as shown in Fig. 3b, the pore size distribution of HPCS calculated by the DFT method clearly suggests this HPCS material has a narrow distribution of pore size centered at 2.73–3.43 nm, which is comparable with ordered mesoporous carbons. The pore size distribution of HPCS shown in Fig. 3c demonstrates the presence of macropore, which should be related to the hollow sphere structure. The HPCS material possesses high surface area, large pore volume and suitable pore size, which makes it to be a good adsorbent for removal phenol from aqueous solution. Adsorption isotherms at room temperature under neutral conditions are shown in Fig. 4. Adsorption isotherms show that the HPCS has an impressive adsorption capacity, which is overwhelmingly higher than those of traditional adsorbents, such as CMK-3 and AC. The Langmuir isotherm model and Freundlich isotherm model are used to describe the adsorption behavior of phenol on HPCS. The adsorption isotherm data can be well-fitted by the Langmuir model (Fig. S1, Supporting information), indicating a monolayer adsorption behavior with excellently high adsorption capacity (Table S1). The calculated maximum adsorption capacity of phenol on HPCS is up to 277.1 mg g 1 which is much larger than 194.9 and 95.2 mg g 1 of the compared sample CMK-3 and AC, respectively, as well as larger than those of reported phenolic sorbents [14,15].
4. Conclusion In summary, a facile synthesis strategy has been successfully developed for preparing HPCS materials by one-step activation treatment to obtain hollow and porous structure simultaneously. The HPCS materials possess very high surface area, large pore
Fig. 1. The XRD patterns (a) and FTIR spectra of (b) Fe3O4, Fe3O4@C and HPCS materials.
B. Chang et al. / Materials Letters 126 (2014) 13–16
15
Fig. 2. SEM (a and b) and TEM (c and d) images of HPCS material.
Fig. 3. N2 adsorption–desorption isotherm (a) and the pore size distribution (b and c) of HPCS material.
volume and narrow pore size distribution, and meanwhile the batch adsorption tests indicate that HPCS has an excellent adsorption capacity for phenol, and its equilibrated adsorption amount is much higher than those of the conventional adsorbents. Consequently, the HPCS material can be used as a good adsorbent to remove phenol from waste water. Furthermore, the synthesis method is quite facile and economical for preparing other hollow porous carbon materials. These materials will find many applications in sorption, catalysis and energy storage.
Acknowledgments
Fig. 4. Adsorption isotherm curve of phenol over different adsorbents material at room temperature.
The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China (21001093), 521 talent project of ZSTU, the project-sponsored by the Scientific
16
B. Chang et al. / Materials Letters 126 (2014) 13–16
Research Foundation (SRF) for the Returned Overseas Chinese Scholars (ROCS), State Education Ministry (SEM), Zhejiang Provincial Natural Science Foundation of China (No. LQ13B020006).
[3] [4] [5] [6] [7]
Appendix A. Supporting information
[8]
Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2014.03. 177.
[9] [10] [11] [12] [13]
References
[14]
[1] Chen M, Wu L, Zhou S, You B. Adv Mater 2006;18:801–6. [2] Wang Q, Yan J, Wang YB, Ning GD, Fang ZJ, Wei T, et al. 2013;52:209–18.
[15] Carbon
Titirici MM, Antonietti M, Thomas A. Chem Mater 2006;18:3808–12. Yang S, Feng X, Zhi L, Cao Q, Maier J, Mullen K. Adv Mater 2010;22:838–42. Liu B, Zeng HC. Small 2005;1:566–71. Arnal PM, Schuth F, Kleitz F. Chem Commun 2006:1203–5. Yang ZC, Zhang Y, Kong JH, Wong SY, Li X, Wang J. Chem Mater 2013;25:704–10. Chang BB, Tian YL, Shi WW, Liu JY, Xi FN, Dong XP. RSC Adv 2013;3:20999–1006. Shuter B, Li X, Wang J. Adv Funct Mater 2010;20:722–31. Chen FH, Gao Q, Ni JZ. Nanotechnology 2008;19:1–9. Chang BB, Fu J, Tian YL, Dong XP. J. Phys Chem C 2013;117:6252–8. Yang ZC, Tang CH, Gong H, Li X, Wang J. J. Power Sources 2013;240:713–20. Tian WQ, Wu XY, Wang KX, Jiang YM, Wang JF, Chen JS. RSC Adv 2013;3:10823–7. Mohanty K, Jha M, Meikap BC, Biswas MN. Ind Eng Chem Res 2005;44:4128–38. Senturk HB, Ozdes D, Gundogdu A, Duran C, Soylak M. J. Hazard Mater 2009;172:353–62.