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Synthesis of carbon nano- and microspheres using palm olein as the carbon source
Materials Letters 78 (2012) 205–208
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of carbon nano- and microspheres using palm olein as the carbon source S.A.M. Zobir a, b,⁎, S. Abdullah a, b, Z. Zainal d, S.H. Sarijo b, M. Rusop a, c a
NANO-SciTech Centre, Institute of Science, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia c NANO-Electronic Centre, Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia d Faculty of Science, Universiti Putra Malaysia (UPM), 43400 UPM Serdang, Selangor, Malaysia b
a r t i c l e
i n f o
Article history: Received 26 October 2011 Accepted 10 March 2012 Available online 22 March 2012 Keywords: Amorphous carbon Chemical vapor deposition Raman spectroscopy Micro- and nanospheres Field Emission Electron Microscopy (FESEM)
a b s t r a c t Carbon nano- and microspheres were synthesized using a dual-furnace chemical vapor deposition method at 800–1000 °C. Palm olein (PO) and zinc nitrate solution were used as a carbon source and catalyst precursor, respectively; with a PO to zinc nitrate ratio of 30:20 (v/v). At 800 °C, no regular microspheres were formed, while a more uniform structure was observed at 900 °C and 1000 °C. Generally, the size of the microspheres is temperature-dependent. The carbon spheres are composed of graphite and amorphous carbon phases and the formation of amorphous carbon was found to be the optimum at 850 °C. This study demonstrates a successful method of carbon nano- and microsphere preparation using PO, a renewable bioresource, as the carbon source for the production of carbon spheres with tailor-made properties. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
1000 oC
intensity/arbitrary units
Since the discovery of carbon onions, composed of concentric spherical graphene shells, intense research has focused on these novel materials, in order to understand their formation mechanism. Currently, several methods have been developed to synthesize carbon microspheres, such as carbon-arc method, high-energy electron irradiation, plasma torch process and the chemical vapor deposition method (CVD) [1–3]. The CVD method is well-established and was used for the infiltration of numerous carbon precursors, such as sucrose, glucose, xylose, furfuryl alcohol and benzene, for the synthesis of mesoporous carbon spheres [4]. Furthermore, it was reported that carbon spheres can be synthesized by direct pyrolysis of hydrocarbons using stryrene, toloune, benzene, cyclohexane and hexane as carbon precursors [5]. Morphological studies indicate that the optimum deposition temperature is 900 °C, resulting in an average diameter distribution of 100– 400 nm. In addition, it was found that the properties of carbon microspheres can be enhanced using boron as a doping agent [6]. Lately, the properties of microspheres have been stretched beyond conventional applications such as nanocomposites, wear-resistant and magnetic storage materials [7] and drug carriers [8]. Here, we describe our work on the synthesis and characterization of carbon nano- and microspheres using PO and zinc nitrate as the carbon and catalyst precursor, respectively.
900 oC
800 oC
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40
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80
2 /degrees ⁎ Corresponding author at: Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia. Tel.: + 60 133449392; fax: + 60 355443870. E-mail address: [email protected] (S.A.M. Zobir). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.032
Fig. 1. XRD patterns of carbon nano- and microspheres obtained by pyrolysis of palm olein (the carbon source) in the presence of zinc nitrate (the catalyst precursor) at 800, 900 and 1000 °C, (◊ = other types of carbon, ♦ = oxide of carbon, ∇ = zinc oxide).
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2. Materials and methods Zinc nitrate hexahydrate (Systerm) and hexamethyltetraamine (Riedel-de-Haen) were used without further purification. A silicon wafer (Polishing Corp of America) was used as a target substrate. The catalyst was prepared by mixing 0.05 M zinc nitrate with PO at a ratio of 30 PO:20 Zn(NO3)2 for 30 min (v/v). The synthesis was conducted using a dual furnace system, with 2 furnaces placed in parallel: Furnace 1 and Furnace 2. The substrate was placed at the center of Furnace 2, and the mixture solution was placed in Furnace 1, in a 3.5 cm diameter quartz tube. Stoppers
were inserted at both ends of the quartz tube. A gas carrier, nitrogen with optimized flow rate of 150 sccm/min was flushed into the tube to create an inert atmosphere. Furnace 2 was first switched on and heated to 800, 900 and 1000 °C, followed by heating Furnace 1 to 500 °C. Deposition was allowed to proceed for an hour, followed by a 30 min annealing. A Field Emission Scanning Electron Microscope (FESEM) (Zeiss, Supra 40VP), a Raman Spectrophotometer (Horiba Jobin Yvon DU420A-OE325) equipped with a 514 nm laser, a Shimadzu XRD-6000 diffractometer using CuKα radiation (λ =1.5405 Å) at 40 kV and 30 mA, at the rate of 2°min− 1 were used for the characterizations.
a
b
c
d
e
Fig. 2. Surface morphology of carbon nano- and microspheres synthesized at (a) 800, (b) 850, 900 and (d) 1000 °C using palm olein as the carbon source. Lower (right) and higher (left) magnification images, and a typical EDX analysis of the carbon spheres (e) are shown.
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207
however the presence of smaller size microspheres can still be observed. The surface morphology study shows that a more uniform size distribution can be obtained for carbon micro- and nanospheres prepared at 850–900 °C; demonstrating that the temperature is very critical in determining the shape and size distribution of the resulting carbon spheres. A typical EDX spectrum (Fig. 2e) shows the presence of carbon, oxygen and zinc elements in all of the samples, indicating that the samples are mainly composed of carbon. The presence of Zn is due to the Zn catalyst, while the Al and Si are due to the sample stub and sample target, respectively. The carbon spheres show an annular coaxial lamellar morphology with only a few nanometers thick (Fig. 3b). The presence of coaxial lamellae was also supported by HRTEM images (Fig. 3c–f), showing a multi-walled structure with a thickness of around 25–30 nm. The metal oxide plays an important role in releases lattice oxygen. As a result, the released atomic oxygen on the catalyst surface oxidises the carbon source and takes away the hydrogen atoms to form water vapor, resulting in the formation of various carbon ring structures; pentagon, heptagon and their combinations. Subsequently, the spheres are formed from a pentagon carbon ring as the nucleus followed by spiral shell growth. In addition, the sphere grows larger when graphitic flakes are nucleated on the surface due to the formation of various paired pentagonal–heptagonal carbon rings, and the combination produces various graphitic configurations for forming the sphere, as was proposed earlier [11]. Raman study revealing two peaks, a D and G band at approximately 1354 and 1583 cm− 1, respectively (Fig. 4). The G band is associated with graphitic nanocrystallites [9] while the D band is due to defects,
3. Results and discussion Fig. 1 shows the presence of zinc oxide together with various forms of carbon, indicating the formation of a carbon phase from the pyrolysis of PO. The XRD patterns exhibit reflections at approximately 26°, which is attributed to the (002) diffraction plane of hexagonal graphite; confirming the presence of a graphitic phase in the samples. However, based on Raman spectroscopy analysis, the presence of an amorphous carbon phase cannot be ruled out, as will be discussed later. FESEM analysis revealed that the carbon nano- and microspheres were successfully deposited on the silicon wafer substrate, at a pyrolysis temperature range of 800–1000 °C. This demonstrates that the size and shape of the resulting carbon spheres is temperature-dependent: no regular microspheres were formed at 800 °C (Fig. 2a), but a drastical transformation to micron scale diameters was observed at 850 °C. In addition, the diameter distribution of the carbon microspheres is more uniform at 850 °C, with an approximate size of 1–3 μm. A closer look at the surface of the microspheres reveals that it is composed of secondary growth of nanoparticles (Fig. 2b on the right). At 900 °C, the formation of a more uniform distribution of carbon nanospheres was observed with diameters between 25 and 35 nm (Fig. 2c). At this temperature, the smallest carbon spheres were also observed. Based on this observation, we hypothesize that the secondary growth of carbon nanoparticles on the surface of carbon microspheres prepared at 850 °C was transformed into carbon nanospheres when the deposition temperature was increased to 900 °C. Interestingly, at 1000 °C the formation of larger carbon microspheres was observed again, but with a uniform particle size distribution,
b
a
c
d
200 nm
50 nm
Fig. 3. FESEM micrograph of carbon spheres prepared by pyrolysis of palm olein (a) at 850 °C, revealing an annular coaxial lamellar morphology, (b) the same FESEM micrograph at higher magnification. HRTEM images of the carbon spheres (c–f).
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Fig. 4. (a) Raman D (left) and G bands (right) (b) the wavenumber shift of the D band, (c) and G band and (d) ID/IG ratios of samples prepared at various pyrolysis temperatures.
attributed to the presence of a non-graphitic, amorphous carbon phase in the structure (Fig. 3a). The D band is quite broad, indicating that an amorphous phase co-exists in the resulting materials. The D and G bands were generally red shifted from 1350 to 1358 cm− 1 and 1568 to 1593 cm− 1, respectively when the deposition temperature was increased from 800 to 1000 °C (Fig. 3b and c); in agreement with previous observations [6]. The ID/IG ratio can be used to indicate the structural ratio of the non-graphitic phase to the graphitic structure [1], and as an indication of the quality and crystallinity of the resulting carbon spheres [10]. A plot of ID/IG (Fig. 4d) and FESEM study (Fig. 2b) suggests that the optimum pyrolysis temperature is 850 °C for the formation of less graphitic content of carbon microspheres but with better size distribution. However, more graphitic content of the carbon spheres was observed at 800 and 1000 °C. This strongly indicates that deposition temperature plays an important role in the formation of either less- or rich-graphitic content of the carbon spheres. Under our experimental condition, the higher ID/IG ratio correlates with carbon spheres with a more uniform particle size distribution. In addition, carbon nanospheres with a diameter of approximately 25–35 nm were observed at 900 °C, with an ID/IG ratio of 1.027. 4. Conclusion Carbon nano- and microspheres were successfully synthesized by pyrolysis of PO between 850 and 1000 °C and their shapes, size
distribution and graphitic content are temperature-dependent. This study demonstrates that PO, a renewable bioresource, can be used as a cheap carbon source for the production of carbon spheres. Acknowledgements The authors would like to thank the Malaysian Government for the funding of the project, Mr. Abdul Karim Ishak, The Microscopy Imaging Centre, Faculty of Pharmacy, UiTM Puncak Alam Campus for HRTEM, and UiTM and Faculty of Applied Science for SKS assistantship for SAMZ. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Gao F, Zhang L, Huang S. Appl Surf Sci 2010;256:232. Qian H, Han F, Zhang B, Guo Y, Yue J, Peng B. Carbon 2004;42:761. Yang Y, Liu X, Guo M, Li S, Liu W, Xu B. Colloid Surf A 2011;377:379. Li Y, Yang Y, Shi J, Ruan M. Microporous Mesoporous Mater 2008;112:597. Jin YZ, Gao C, Hsu WK, Zhu Y, Huczko A, Bystrzejewski M, et al. Carbon 2005;43:1944. Mondal KC, Strydom AM, Tetana Z, Mhlanga SD, Witcomb MJ, Havel J, et al. Mater Chem Phys 2009;114:973. Shu K, Qin Y, Luo H, Zhang P, Guo Z. Mater Lett 2011;65:1510. Zhang X, Hui Z, Wan D, Huang H, Huang J, Yuan H, et al. Int J Biol Macromol 2010;47:389. Lupu D, Biris AR, Watanabe F, Li Z, Dervishi E, Saini V, et al. Chem Phys Lett 2009;473:299. Xie Y, Huang Q, Huang B. Carbon 2010;48:2023. Wang ZL, Kang ZC. J Phys Chem 1996;100:17725.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis of carbon nano- and microspheres using palm olein as the carbon source S.A.M. Zobir a, b,⁎, S. Abdullah a, b, Z. Zainal d, S.H. Sarijo b, M. Rusop a, c a
NANO-SciTech Centre, Institute of Science, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia c NANO-Electronic Centre, Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia d Faculty of Science, Universiti Putra Malaysia (UPM), 43400 UPM Serdang, Selangor, Malaysia b
a r t i c l e
i n f o
Article history: Received 26 October 2011 Accepted 10 March 2012 Available online 22 March 2012 Keywords: Amorphous carbon Chemical vapor deposition Raman spectroscopy Micro- and nanospheres Field Emission Electron Microscopy (FESEM)
a b s t r a c t Carbon nano- and microspheres were synthesized using a dual-furnace chemical vapor deposition method at 800–1000 °C. Palm olein (PO) and zinc nitrate solution were used as a carbon source and catalyst precursor, respectively; with a PO to zinc nitrate ratio of 30:20 (v/v). At 800 °C, no regular microspheres were formed, while a more uniform structure was observed at 900 °C and 1000 °C. Generally, the size of the microspheres is temperature-dependent. The carbon spheres are composed of graphite and amorphous carbon phases and the formation of amorphous carbon was found to be the optimum at 850 °C. This study demonstrates a successful method of carbon nano- and microsphere preparation using PO, a renewable bioresource, as the carbon source for the production of carbon spheres with tailor-made properties. © 2012 Elsevier B.V. All rights reserved.
1. Introduction
1000 oC
intensity/arbitrary units
Since the discovery of carbon onions, composed of concentric spherical graphene shells, intense research has focused on these novel materials, in order to understand their formation mechanism. Currently, several methods have been developed to synthesize carbon microspheres, such as carbon-arc method, high-energy electron irradiation, plasma torch process and the chemical vapor deposition method (CVD) [1–3]. The CVD method is well-established and was used for the infiltration of numerous carbon precursors, such as sucrose, glucose, xylose, furfuryl alcohol and benzene, for the synthesis of mesoporous carbon spheres [4]. Furthermore, it was reported that carbon spheres can be synthesized by direct pyrolysis of hydrocarbons using stryrene, toloune, benzene, cyclohexane and hexane as carbon precursors [5]. Morphological studies indicate that the optimum deposition temperature is 900 °C, resulting in an average diameter distribution of 100– 400 nm. In addition, it was found that the properties of carbon microspheres can be enhanced using boron as a doping agent [6]. Lately, the properties of microspheres have been stretched beyond conventional applications such as nanocomposites, wear-resistant and magnetic storage materials [7] and drug carriers [8]. Here, we describe our work on the synthesis and characterization of carbon nano- and microspheres using PO and zinc nitrate as the carbon and catalyst precursor, respectively.
900 oC
800 oC
20
40
60
80
2 /degrees ⁎ Corresponding author at: Universiti Teknologi MARA (UiTM), 40450 Shah Alam, Selangor, Malaysia. Tel.: + 60 133449392; fax: + 60 355443870. E-mail address: [email protected] (S.A.M. Zobir). 0167-577X/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2012.03.032
Fig. 1. XRD patterns of carbon nano- and microspheres obtained by pyrolysis of palm olein (the carbon source) in the presence of zinc nitrate (the catalyst precursor) at 800, 900 and 1000 °C, (◊ = other types of carbon, ♦ = oxide of carbon, ∇ = zinc oxide).
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S.A.M. Zobir et al. / Materials Letters 78 (2012) 205–208
2. Materials and methods Zinc nitrate hexahydrate (Systerm) and hexamethyltetraamine (Riedel-de-Haen) were used without further purification. A silicon wafer (Polishing Corp of America) was used as a target substrate. The catalyst was prepared by mixing 0.05 M zinc nitrate with PO at a ratio of 30 PO:20 Zn(NO3)2 for 30 min (v/v). The synthesis was conducted using a dual furnace system, with 2 furnaces placed in parallel: Furnace 1 and Furnace 2. The substrate was placed at the center of Furnace 2, and the mixture solution was placed in Furnace 1, in a 3.5 cm diameter quartz tube. Stoppers
were inserted at both ends of the quartz tube. A gas carrier, nitrogen with optimized flow rate of 150 sccm/min was flushed into the tube to create an inert atmosphere. Furnace 2 was first switched on and heated to 800, 900 and 1000 °C, followed by heating Furnace 1 to 500 °C. Deposition was allowed to proceed for an hour, followed by a 30 min annealing. A Field Emission Scanning Electron Microscope (FESEM) (Zeiss, Supra 40VP), a Raman Spectrophotometer (Horiba Jobin Yvon DU420A-OE325) equipped with a 514 nm laser, a Shimadzu XRD-6000 diffractometer using CuKα radiation (λ =1.5405 Å) at 40 kV and 30 mA, at the rate of 2°min− 1 were used for the characterizations.
a
b
c
d
e
Fig. 2. Surface morphology of carbon nano- and microspheres synthesized at (a) 800, (b) 850, 900 and (d) 1000 °C using palm olein as the carbon source. Lower (right) and higher (left) magnification images, and a typical EDX analysis of the carbon spheres (e) are shown.
S.A.M. Zobir et al. / Materials Letters 78 (2012) 205–208
207
however the presence of smaller size microspheres can still be observed. The surface morphology study shows that a more uniform size distribution can be obtained for carbon micro- and nanospheres prepared at 850–900 °C; demonstrating that the temperature is very critical in determining the shape and size distribution of the resulting carbon spheres. A typical EDX spectrum (Fig. 2e) shows the presence of carbon, oxygen and zinc elements in all of the samples, indicating that the samples are mainly composed of carbon. The presence of Zn is due to the Zn catalyst, while the Al and Si are due to the sample stub and sample target, respectively. The carbon spheres show an annular coaxial lamellar morphology with only a few nanometers thick (Fig. 3b). The presence of coaxial lamellae was also supported by HRTEM images (Fig. 3c–f), showing a multi-walled structure with a thickness of around 25–30 nm. The metal oxide plays an important role in releases lattice oxygen. As a result, the released atomic oxygen on the catalyst surface oxidises the carbon source and takes away the hydrogen atoms to form water vapor, resulting in the formation of various carbon ring structures; pentagon, heptagon and their combinations. Subsequently, the spheres are formed from a pentagon carbon ring as the nucleus followed by spiral shell growth. In addition, the sphere grows larger when graphitic flakes are nucleated on the surface due to the formation of various paired pentagonal–heptagonal carbon rings, and the combination produces various graphitic configurations for forming the sphere, as was proposed earlier [11]. Raman study revealing two peaks, a D and G band at approximately 1354 and 1583 cm− 1, respectively (Fig. 4). The G band is associated with graphitic nanocrystallites [9] while the D band is due to defects,
3. Results and discussion Fig. 1 shows the presence of zinc oxide together with various forms of carbon, indicating the formation of a carbon phase from the pyrolysis of PO. The XRD patterns exhibit reflections at approximately 26°, which is attributed to the (002) diffraction plane of hexagonal graphite; confirming the presence of a graphitic phase in the samples. However, based on Raman spectroscopy analysis, the presence of an amorphous carbon phase cannot be ruled out, as will be discussed later. FESEM analysis revealed that the carbon nano- and microspheres were successfully deposited on the silicon wafer substrate, at a pyrolysis temperature range of 800–1000 °C. This demonstrates that the size and shape of the resulting carbon spheres is temperature-dependent: no regular microspheres were formed at 800 °C (Fig. 2a), but a drastical transformation to micron scale diameters was observed at 850 °C. In addition, the diameter distribution of the carbon microspheres is more uniform at 850 °C, with an approximate size of 1–3 μm. A closer look at the surface of the microspheres reveals that it is composed of secondary growth of nanoparticles (Fig. 2b on the right). At 900 °C, the formation of a more uniform distribution of carbon nanospheres was observed with diameters between 25 and 35 nm (Fig. 2c). At this temperature, the smallest carbon spheres were also observed. Based on this observation, we hypothesize that the secondary growth of carbon nanoparticles on the surface of carbon microspheres prepared at 850 °C was transformed into carbon nanospheres when the deposition temperature was increased to 900 °C. Interestingly, at 1000 °C the formation of larger carbon microspheres was observed again, but with a uniform particle size distribution,
b
a
c
d
200 nm
50 nm
Fig. 3. FESEM micrograph of carbon spheres prepared by pyrolysis of palm olein (a) at 850 °C, revealing an annular coaxial lamellar morphology, (b) the same FESEM micrograph at higher magnification. HRTEM images of the carbon spheres (c–f).
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Fig. 4. (a) Raman D (left) and G bands (right) (b) the wavenumber shift of the D band, (c) and G band and (d) ID/IG ratios of samples prepared at various pyrolysis temperatures.
attributed to the presence of a non-graphitic, amorphous carbon phase in the structure (Fig. 3a). The D band is quite broad, indicating that an amorphous phase co-exists in the resulting materials. The D and G bands were generally red shifted from 1350 to 1358 cm− 1 and 1568 to 1593 cm− 1, respectively when the deposition temperature was increased from 800 to 1000 °C (Fig. 3b and c); in agreement with previous observations [6]. The ID/IG ratio can be used to indicate the structural ratio of the non-graphitic phase to the graphitic structure [1], and as an indication of the quality and crystallinity of the resulting carbon spheres [10]. A plot of ID/IG (Fig. 4d) and FESEM study (Fig. 2b) suggests that the optimum pyrolysis temperature is 850 °C for the formation of less graphitic content of carbon microspheres but with better size distribution. However, more graphitic content of the carbon spheres was observed at 800 and 1000 °C. This strongly indicates that deposition temperature plays an important role in the formation of either less- or rich-graphitic content of the carbon spheres. Under our experimental condition, the higher ID/IG ratio correlates with carbon spheres with a more uniform particle size distribution. In addition, carbon nanospheres with a diameter of approximately 25–35 nm were observed at 900 °C, with an ID/IG ratio of 1.027. 4. Conclusion Carbon nano- and microspheres were successfully synthesized by pyrolysis of PO between 850 and 1000 °C and their shapes, size
distribution and graphitic content are temperature-dependent. This study demonstrates that PO, a renewable bioresource, can be used as a cheap carbon source for the production of carbon spheres. Acknowledgements The authors would like to thank the Malaysian Government for the funding of the project, Mr. Abdul Karim Ishak, The Microscopy Imaging Centre, Faculty of Pharmacy, UiTM Puncak Alam Campus for HRTEM, and UiTM and Faculty of Applied Science for SKS assistantship for SAMZ. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Gao F, Zhang L, Huang S. Appl Surf Sci 2010;256:232. Qian H, Han F, Zhang B, Guo Y, Yue J, Peng B. Carbon 2004;42:761. Yang Y, Liu X, Guo M, Li S, Liu W, Xu B. Colloid Surf A 2011;377:379. Li Y, Yang Y, Shi J, Ruan M. Microporous Mesoporous Mater 2008;112:597. Jin YZ, Gao C, Hsu WK, Zhu Y, Huczko A, Bystrzejewski M, et al. Carbon 2005;43:1944. Mondal KC, Strydom AM, Tetana Z, Mhlanga SD, Witcomb MJ, Havel J, et al. Mater Chem Phys 2009;114:973. Shu K, Qin Y, Luo H, Zhang P, Guo Z. Mater Lett 2011;65:1510. Zhang X, Hui Z, Wan D, Huang H, Huang J, Yuan H, et al. Int J Biol Macromol 2010;47:389. Lupu D, Biris AR, Watanabe F, Li Z, Dervishi E, Saini V, et al. Chem Phys Lett 2009;473:299. Xie Y, Huang Q, Huang B. Carbon 2010;48:2023. Wang ZL, Kang ZC. J Phys Chem 1996;100:17725.