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Nano magnetite decorated multiwalled carbon nanotubes: a robust nanomaterial for enhanced carbon dioxide adsorption Ashish Kumar Mishra and Sundara Ramaprabhu*
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Received 14th May 2010, Accepted 21st October 2010 DOI: 10.1039/c0ee00076k It has long been seen as a demanding task to counteract the raised levels of greenhouse gases including carbon dioxide (CO2). Current worldwide research is focused on the investigation of materials which can capture large amounts of CO2 through physical or chemical adsorption. The present work focuses on a high pressure CO2 adsorption study of functionalized MWNTs (f-MWNTs) and a magnetite decorated MWNT nanocomposite. Multiwalled carbon nanotubes (MWNTs) were prepared by a catalytic chemical vapor deposition method followed by purification and functionalization. Magnetite (Fe3O4) nanoparticles were decorated over the f-MWNT surface by a chemical method. The functionalized MWNTs and magnetite decorated MWNTs were characterized by electron microscopy, X-ray powder diffraction, Raman spectroscopy and FTIR spectroscopy. The CO2 adsorption capacity was measured using high pressure Sieverts’ apparatus. A large enhancement in the CO2 adsorption capacity was achieved by decorating magnetite nanoparticles over the MWNT surface.
Introduction The growing need for fossil fuel energy poses a great challenge for the control of CO2 emissions in our atmosphere. As a result, innovations like carbon capture technology would allow us to maintain optimum CO2 levels. Among all the means to reduce its global emission, the geological sequestration and storage options for CO2 are both environmentally and economically beneficial and thus have attracted worldwide attention among researchers. The possible sites for geological sequestration of CO2 include unminable coal seams, abandoned and sealed mines, active or depleted oil and gas reservoirs, deep saline aquifers, and salt caverns.1,2 As an alternative method for CO2 capture, adsorption can be considered to be one of the more promising methods, offering potential energy savings compared to absorbent systems, espe-
Alternative Energy and Nanotechnology Laboratory (AENL), Nano Functional Materials Technology Centre (NFMTC), Department of Physics, Indian Institute of Technology, Madras, Chennai, 600036, India. E-mail:
[email protected]
cially with respect to compression costs.3,4 Previously, pressure swing adsorption (PSA) using solid sorbents has gained interest due to its low energy and capital investment costs.5,6 In terms of achieving high adsorption capacities, activated carbons (ACs) and zeolite-based molecular sieves have shown much promise. ACs generally give higher additional capacity at pressures greater than atmospheric compared to zeolites. Further, ACs are often preferred over zeolites because of their relatively moderate strengths of adsorption for gases, which facilitates easier desorption.7–9 Activated carbons are sorbents with a highly developed porosity, especially micro- and mesopores, used in a wide range of industrial applications. CO2 adsorption capacities of activated carbons depend on their pore structure but also on the surface chemistry properties.10,11 One dimensional carbon based nanostructures like single-walled and multiwalled carbon nanotubes can provide a good alternative for this purpose due to their large surface area and high porosity.12 Some metals (like zero valent iron) have been reported for the reduction of CO2.13 Metal oxides are important heterogeneous catalysts and the interaction of CO2 with oxide surfaces is of great interest. There have been spectroscopy studies of CO2
Broader context In order to reduce global warming, the investigation of high performance CO2 adsorbents is a major area of current scientific research. In the present work, we have demonstrated for the first time an Fe3O4-MWNT nanocomposite as a CO2 adsorbent with very high CO2 uptake capacity. This novel nanocomposite exhibits almost five times the CO2 adsorption capacity of activated carbon and almost twelve times that of 13X zeolite at the same pressure and temperature. In addition, it has a high CO2 uptake capacity even up to 100 C, which makes this nanocomposite a suitable CO2 adsorbent for industrial (cement industries, thermal power plants etc.) exhaust. Reversibility of the adsorption capacity after evacuation at 150 C under vacuum gives an advantage to this nanocomposite for commercial use. Desorbed CO2 can be utilized for other purposes like food packaging. Hence the adsorption and desorption of CO2 with the Fe3O4-MWNT nanocomposite makes this novel nanocomposite suitable for commercial use. In addition this study provides a platform to investigate similar nanocomposites with other low cost porous carbon materials and large scale production of such nanocomposites could allow developing countries to reduce their CO2 emissions without affecting their growth rate. This journal is ª The Royal Society of Chemistry 2011
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adsorption on hydroxylated metal oxide surfaces, including iron oxide and oxide-supported metal catalysts. The formation of adsorbed carbonates, bicarbonates and carboxylates, as well as bent CO2 species, has been observed in some of the metal oxides (Fe2O3, Al2O3).14 It is important to develop composite materials which can adsorb CO2 at elevated pressure and at room temperature. The large surface area and porosity of CNTs and the CO2 adsorption ability of hydroxylated nanometal oxide surfaces motivated us to study the CO2 adsorption ability of magnetite nanoparticle decorated MWNTs at high pressures of CO2. In the present work, MWNTs and a Fe3O4-MWNT nanocomposite were systematically prepared and characterized for their interaction with CO2 and the results have been discussed with reference to the pore adsorption behavior of MWNTs.
Energy dispersive X-ray (EDX) analysis confirms the presence of iron, oxygen and carbon in this nanocomposite (Fig. 1d).
X-Ray diffractogram analysis The XRD pattern in Fig. 2 indicates the crystalline nature of the magnetic nanocomposite. The XRD pattern of functionalized MWNTs exhibits a single carbon peak at a 2q value of 26.2 which corresponds to the graphitic layered structure of the nanotubes. The XRD pattern of the magnetic nanocomposite
Results and discussion Morphological study The morphological studies of the prepared nanocomposite were carried out by electron microscopy techniques. SEM and TEM photographs of the nanocomposite clearly suggest the uniform decoration of magnetite nanoparticles over the surface of MWNTs (Fig. 1a and b). A high resolution TEM image (Fig. 1c) clearly suggests the crystalline nature of the magnetite nanoparticles and MWNTs. These photographs suggest an inner diameter of 5–10 nm and outer diameter of 30–50 nm for the MWNTs. The particle size of magnetite ranges from 5–8 nm.
Fig. 2 X-Ray diffraction patterns for f-MWNTs and the magnetiteMWNT nanocomposite.
Fig. 1 (a) SEM, (b) TEM, (c) HRTEM and (d) EDX analysis of the magnetite-MWNT nanocomposite.
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exhibits magnetite peaks at 2q values of 30.3 , 35.6 , 43.3 , 53.6 , 57.4 , 62.8 and 74.6 along with the carbon peak at 26.2 . These peaks correspond to the face centered cubic structure of magnetite nanoparticles. Thus the XRD pattern of the nanocomposite suggests the formation of two phases, one of cubic magnetite nanoparticles and the other of a coaxial arrangement of cylindrical MWNTs.15 X-Ray photoelectron spectroscopy analysis of the nanocomposite Formation of the magnetic nanocomposite was also confirmed by XPS analysis. Magnesium Ka radiation was used for X-ray generation. Fig. 3a is the wide scan spectrum of the sample in which the photoelectron lines at binding energies of about 285, 530 and 711 eV are attributed to C 1s, O 1s and Fe 2p, respectively. In Fig. 3b, the peaks of Fe 2p1/2 and Fe 2p3/2 located at 710.9 and 725 eV further confirm that the oxide in the sample is Fe3O4. Fig. 3c shows the core-level spectrum of C 1s and the peaks at 284, 284.6 and 285.8 eV correspond to sp2-hybridized carbon, defect-containing sp2-hybridized carbon and sp3 defects of MWNTs, respectively. An additional peak was observed at 288.6 eV, which may correspond to the carbon atoms in carboxylic groups (–COO) at the surface of MWNTs due to functionalization.15–17 BET surface area measurements BET surface area measurements of MWNTs and the Fe3O4MWNT nanocomposite are shown in Fig. 4. A large hysteresis area is observed for the N2 adsorption–desorption isotherm in the case of pure MWNTs and the nanocomposite. This suggests a wide distribution of pore sizes in both cases. The specific surface area calculated by using the BET equation is found to be 91.96 m2 g1 and 70.09 m2 g1 for MWNTs and the nanocomposite, respectively. Nearly uniform pore size with the pore radius in the range 1.7–2.5 nm and a pore volume of 0.22 cm3 g1 was observed for MWNTs. In the case of the Fe3O4-MWNT nanocomposite, uniform pore size with the pore radius in the range 3–6 nm and a pore volume of 0.23 cm3 g1 was observed. The large hysteresis area of the N2 adsorption–desorption isotherm in the case of the nanocomposite suggests the wide
Fig. 3 X-Ray photoelectron spectroscopy of the magnetite-MWNT nanocomposite.
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Fig. 4 BET surface area measurements of f-MWNTs and the magnetiteMWNT nanocomposite.
distributions of pores in the nanocomposite even after the decoration of iron oxide nanoparticles over the pure MWNTs surface.
Raman spectrogram analysis Fig. 5 shows the Raman spectrogram of the f-MWNTs and Fe3O4-MWNT nanocomposite. Raman spectroscopic analysis of the f-MWNTs shows a comparable intensity of the D-band (1336.4 cm1) and the G-band (1565.8 cm1), which is due to the presence of more defects at the surface of the MWNTs due to functionalization.18 The G-band corresponds to the tangential modes of vibrations, while the D-band corresponds to the defects of MWNTs.19 A small shift in the G-band (1578.6 cm1) was observed in the case of the magnetic nanocomposite. Along with the shift in the G-band, some extra peaks were observed at lower Raman shift values in the case of the nanocomposite. These extra peaks arise due to the formation of Fe3O4 nanoparticles over the surface of the MWNTs. Peaks at lower Raman shift (225.2, 285.2, 394.8 and 591.4 cm1) values may correspond to vibration modes of Fe–O bonds of Fe3O4 nanoparticles and Fe–C bonds at the surface of the MWNTs.20,21
Fig. 5 Raman spectra of (a) f-MWNTs and CO2 adsorbed f-MWNTs, (b) the magnetite-MWNT nanocomposite and CO2 adsorbed magnetiteMWNT nanocomposite.
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In the case of CO2 adsorbed f-MWNTs, the D-band and Gband did not show any peak shift compared to f-MWNTs. However, in the case of the CO2 adsorbed Fe3O4-MWNT nanocomposite, the G-band shifts to 1583.6 cm1 and the some of the peaks corresponding to the Fe–O and Fe–C bonds shift to higher values (292.4, 397.9 and 603.8 cm1). These peak shifts may correspond to the strong interaction between magnetite nanoparticles and CO2 molecules, which leads to the high level of adsorption of CO2 on the nanocomposite compared to the fMWNTs.
attributed to the asymmetric stretching of CO2 molecules (2332 cm1), (O–C–O) symmetric vibrational mode of bicarbonates (1408 cm1) and (C–O) symmetric vibrational mode of carbonates (1077 cm1). Some amount of bicarbonates and carbonates may be due to the strong interaction of CO2 with the hydroxyl groups attached to the Fe3O4 nanoparticles of the nanocomposite.14,22 Besides, larger shifts were observed for the peaks of the nanocomposite compared to the MWNTs. This may be due to greater CO2 adsorption in the case of the Fe3O4-MWNT nanocomposite compared to the MWNTs.
Fourier transform infrared spectrogram analysis
Adsorption isotherm studies
Fig. 6 shows the FTIR spectrum of f-MWNTs and the Fe3O4MWNT nanocomposite. The FTIR study of f-MWNTs confirms the defect sites at the surface of MWNTs and the presence of >C]C (1635 cm1), >C]O (1022 cm1), ¼CH2 (2852, 2925 cm1) and –OH (3437 cm1) functional groups at the surface of the MWNTs, while a peak at 1405 cm1 may be due to the carboxylic group (–COO) attached to the MWNTs.16,19 These functional groups at the surface of the MWNTs provide anchoring sites for metal and metal oxide nanoparticles. This helps in the decoration of the MWNT surface by Fe3O4 nanoparticles. The FTIR study of the nanocomposite confirms the presence of >C]C (1635, 1720 cm1), >C]O (1020, 1112 cm1), ¼CH2 (2851, 2920 cm1) and –OH (3410 cm1) functional groups on the surface of the nanocomposite. Band shifts were observed for the above functional groups in the case of the nanocomposite, which may be explained as the large positive charge of the ferric/ ferrous ion renders a partial single bond character of the C]O bond which weakens the bond.19 Along with these functional groups, a band is seen at 583 cm1, which may correspond to the stretching vibration of Fe–O–Fe in Fe3O4.15 In the case of the CO2 adsorbed f-MWNTs an addition peak was noticed at 2330 cm1 which corresponds to the asymmetric stretching of CO2 molecules. Along with the asymmetric stretch, a shift was observed in most of the peaks which may be due to the adsorbed CO2 in the pores of nanotubes and the interaction of CO2 with the functional groups (like carbonyl etc.) attached to the surface of MWNTs. In the case of the CO2 adsorbed nanocomposite, some additional peaks were noticed which may be
High pressure adsorption studies were performed using Sievert’s apparatus and by incorporating van der Waals corrections. Adsorption of CO2 over MWNTs and the Fe3O4-MWNT nanocomposite was studied at three different temperatures (25, 50 and 100 C) and high pressures. The amount of CO2 adsorbed in moles was measured by the following equations:
Fig. 6 FTIR spectra of (a) f-MWNTs and CO2 adsorbed f-MWNTs, (b) the magnetite-MWNT nanocomposite and CO2 adsorbed magnetiteMWNT nanocomposite.
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Dnadsorbed ¼ ni (n0 + n00 )
(1)
where ni is the number of moles of CO2 in the initial volume Vi at the known initial pressure Pi. n0 is the number of moles in Vi at equilibrium pressure Peq and n00 is the number of moles in the cell volume Vc at equilibrium pressure Peq. ni, n0 and n00 can be calculated by using the following equations: abni3 + aVini2 + (RT + Pib)Vi2ni PiVi3 ¼ 0
(2)
abn0 3 + aVin0 2 + (RT + Pib)Vi2n0 PiVi3 ¼ 0
(3)
abn00 3 + aVin00 2 + (RT + Pib)Vi2n00 PiVi3 ¼ 0
(4)
where T is the cell temperature and R is the universal gas constant. a and b are the van der Waals coefficients for CO2 gas. Fig. 7 shows the adsorption behavior of the f-MWNTs and nanocomposite at three different temperatures. A maximum adsorption capacity of 0.0594 mol g1 was found for the magnetite-MWNT nanocomposite and 0.0143 mol g1 for the fMWNTs, at 12 bar and room temperature. At 12 bar and 50 C the maximum adsorption capacity was 0.0379 and 0.0101 mol g1 for the nanocomposite and f-MWNTs, respectively. At 12 bar
Fig. 7 Adsorption isotherms at different temperatures for f-MWNTs and the magnetite-MWNT nanocomposite.
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and 100 C the maximum adsorption capacity was 0.0248 and 0.0097 mol g1 for the nanocomposite and f-MWNTs, respectively. It is evident that at each temperature the adsorption capacities of the f-MWNTs and nanocomposite increase with equilibrium pressure, which may be attributed to the condensation of CO2 molecules in mesopores at high pressures. A large enhancement in the CO2 adsorption capacity of the Fe3O4-MWNT nanocomposite compared to the f-MWNTs was observed. Enhancement in the CO2 uptake capacity may be attributed to the additional chemical interaction of CO2 molecules with magnetite nanoparticles in the case of the nanocomposite. In the case of f-MWNTs, CO2 molecules may be attached to the functional groups and may become physically adsorbed in the pores. In the case of the Fe3O4-MWNT nanocomposite, along with physical adsorption in pores and attachment with functional groups, CO2 molecules chemically interact with the Fe3O4 nanoparticles. This chemical interaction of CO2 molecules with the Fe3O4 nanoparticles may lead to the formation of iron bicarbonate and iron carbonate (as suggested by the FTIR spectra) and hence increase the CO2 adsorption capacity of the nanocomposite compared to the f-MWNTs. Comparison with other solid sorbents Cavenati et al. have reported around 0.0032 mol g1 of CO2 adsorption in 13X zeolite at 12 bar pressure and at room temperature (25 C).23 Siriwardane et al. have reported a CO2 uptake capacity of 0.004–0.0045 mol g1 at nearly 12 bar pressure and 25 C for molecular sieve 13X.8 Zhang et al. have reported 0.01–0.015 mol g1 CO2 uptake by activated carbon at around 12 bar pressure and room temperature.24 A high pressure CO2 adsorption study on different metal organic frameworks by Millward and Yaghi demonstrated CO2 adsorption capacities ranging from 0.002–0.01 mol g1 at nearly 12 bar pressure and at room temperature.25 Belmabkhout et al. have reported a CO2 adsorption capacity of 0.005 mol g1 at nearly 12 bar pressure and at room temperature for MCM 41 silica.26 All these reported values are much lower than our value for the Fe3O4-MWNT nanocomposite (0.0594 mol g1 at 12 bar pressure and at room temperature). Temperature dependence Fig. 8 clearly shows the CO2 adsorption dependence on temperature for the f-MWNTs and nanocomposite. This suggests that with an increase in temperature the adsorption capacity of the nanocomposite and MWNTs decreases, which may be due to the higher kinetic energy of CO2 gas molecules at higher temperatures. At lower temperature, the large adsorption capacities of the nanocomposite and f-MWNTs may be attributed to the good interaction of CO2 with magnetite nanoparticles, which helps increase the condensation of CO2 gas in micropores of the nanocomposite as well as a fraction of the bicarbonate formation, due to the hydroxylate groups attached to the iron oxide surface, and carbonate formation. Peaks at 1408 and 1077 cm1 in the FTIR spectra indicate the presence of iron bicarbonate and carbonate, respectively.14
Fig. 8 Temperature dependence of the adsorption capacity of fMWNTs and the magnetite-MWNT nanocomposite.
lnW ¼ lnW0 + (R/E)2[Tln(P0/P)]2
(5)
where W is the amount of adsorbed CO2, W0 is the microporous volume and E is the characteristic adsorption energy. W is given by: W ¼ Dn$M/r
(6)
Where Dn is the amount of CO2 adsorbed in mol g1, M is the molecular weight (M ¼ 44 g) and r is the density of the CO2 adsorbate at a temperature T (r ¼ 0.85 g cc1 at 298 K). The DR method is based on the postulate that the mechanism for adsorption in micropores is that of pore filling rather than a layer-by-layer formation of a film on the walls of the pores. Fig. 9 shows the DR equation fit for f-MWNTs and the Fe3O4MWNT nanocomposite in the pressure region below 8 bar at room temperature (25 C). At high pressures the isotherm deviates from the DR fit, which can be attributed to multilayer adsorption, capillary condensation in the mesopores and the interaction of CO2 with functional groups of f-MWNTs.22,29 In the case of the nanocomposite, a larger deviation occurs due to the additional bicarbonate and carbonate formation along with the above mentioned possibilities. Table 1 shows the DR parameters for f-MWNTs and the nanocomposite. The micropore volume for the f-MWNTs was found to be 0.725 cc g1. This micropore volume for MWNTs is higher than other reported
Dubinin–Radushkevitch (DR) equation The CO2 adsorption isotherms at different temperatures for fMWNTs and the nanocomposite were treated by the DR method.27,28 The DR equation can be represented as follows: This journal is ª The Royal Society of Chemistry 2011
Fig. 9 Dubinin–Radushkevitch fit for f-MWNTs and the magnetiteMWNT nanocomposite.
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Table 1 Adsorbent
W0/cc g1
E/kJ mol1
f-MWNTs Fe3O4-MWNT nanocomposite
0.725 4.862
5.65 4.1
values, which may be attributed to the presence of a large number of mesopores and functional groups in the f-MWNTs. The micropore volume for the Fe3O4-MWNT nanocomposite was found to be 4.862 cc g1. This much larger value of the micropore volume for the nanocomposite may be due to the involvement of chemical bonding (bicarbonate and carbonate formation) along with condensation in mesopores and interaction with functional groups.
Experimental Synthesis of functionalized MWNTs MWNTs were synthesized by the catalytic chemical vapor deposition method. In this method a hydrogen decrepitated AB3 alloy was taken as the catalyst material. Pyrolysis of acetylene takes place at 700 C under inert atmosphere, which results in the growth of MWNTs.30 These MWNTs were further purified by air oxidation followed by acid treatment to remove amorphous carbon and catalytic impurities. These purified MWNTs were further functionalized to make them hydrophilic by stirring of the MWNTs in concentrated nitric acid for 2 h. Functionalization provides anchoring sites for the uniform decoration of metal oxide nanoparticles over the MWNT surface. Decoration of magnetite nanoparticles over MWNT surface Decoration of magnetite nanoparticles over the MWNT surface was carried out by a chemical technique. The functionalized MWNTs were suspended in de-ionised water by ultrasonication. Functional groups at the surface of the MWNTs provide a hydrophilic nature to the MWNTs, which leads to their easy dispersion in water. FeCl3$6H2O and FeSO4$7H2O (Acros Organics) were dissolved in de-ionised water in the stoichiometric ratio of 3 : 2. This solution was heated up to 90 C. An ammonia solution (NH4OH, 25%) and the MWNT dispersed solution were added to the above solution, in the volumetric ratio of 1 : 5. This solution was stirred at 90 C for 30 min and then cooled to room temperature. The black precipitate was collected by filtration and washed to neutral with water. The obtained black precipitate was the Fe3O4-MWNT nanocomposite.15,31 Characterization techniques The Fe3O4-MWNT nanocomposite was characterized by FEI QUANTA 3D scanning electron microcopy (SEM) and Philips JEOL CM12 transmission electron microscopy (TEM). X-Ray powder diffraction analysis was performed using an X0 Pert Pro PANalytical X-ray diffractometer. BET surface area measurements were analyzed using a Micromeritics ASAP 2020 analyzer. Raman analysis was performed by using a HORIBA JOBIN YVON HR800UV Confocal Raman spectrometer, while the FTIR study was performed by using a PERKIN ELMER 894 | Energy Environ. Sci., 2011, 4, 889–895
Fig. 10 Schematic diagram of adsorption setup (Sieverts’ apparatus).
Spectrum One FT-IR spectrometer. X-Ray photoelectron spectroscopy (XPS) analysis was performed by using an Omicron nanotechnology X-ray photoelectron spectrometer. Adsorption studies Adsorption studies were carried out using high pressure Sieverts’ apparatus, which has been frequently used for high pressure hydrogen sorption studies. The experimental setup consists of stainless steel tubes, tees, elbow joints and needle valves procured from NOVA, Switzerland. They can withstand up to 1000 bar pressure. The pressure transducers procured from Burster, Germany are used to monitor the gas pressure in the range 0–50 bar. The schematic presentation of the setup is given in Fig. 10. The weight of samples used of the f-MWNTs and Fe3O4-MWNT nanocomposite was 150 mg in each measurement. A number of cycles were performed to recheck the adsorption capacity and the values were found to be almost consistent. Samples were degassed at 150 C under high vacuum (109 Torr) to regain their adsorptive sites for CO2 and the same sample used again for the adsorption study and the adsorption capacity was found to be repeatable.
Conclusion The present work shows the large enhancement in CO2 adsorption by decorating Fe3O4 nanoparticles over the MWNT surface. This nanocomposite shows a much higher sorption capacity of CO2 compared to other reported solid sorbents. Decoration of magnetite nanoparticles over MWNTs incorporates the adsorption of CO2 in pores, interaction of CO2 with functional groups and chemical interaction of CO2 with iron oxide nanoparticles, which leads to the large increase in CO2 sorption capacity of the nanocomposite. The Fe3O4-MWNT nanocomposite is demonstrated as a potential CO2 sorbent with high sorption capacity.
Acknowledgements The authors acknowledge the support of IITM and DST, India. One of the authors (Ashish) is thankful to DST India for providing financial support. Authors are also thankful to the National Catalytic Research Center and SAIF, IIT Madras for helping in XPS and FTIR analysis. This journal is ª The Royal Society of Chemistry 2011
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References 1 S. Shimada, H. Y. Li, Y. Oshima and K. Adachi, Environ. Geol., 2005, 49, 44. 2 W. N. Sams, G. Bromhal, S. Jikich, T. Ertekin and D. H. Smith, Energy Fuels, 2005, 19, 2287. 3 T. C. Drage, J. M. Blackman, C. Pevida and C. E. Snape, Energy Fuels, 2009, 23, 2790. 4 M. Radosz, X. Hu, K. Krutkramelis and Y. Shen, Ind. Eng. Chem. Res., 2008, 47, 3783. 5 C. W. Skarstrom, U.S. Pat., 2 944 627, 1960. 6 Fuderer and E. Rudelstorfer, U.S. Pat., 3 896 849, 1976. 7 S. Sircar, T. C. Golden and M. B. Rao, Carbon, 1996, 34, 1. 8 R. V. Siriwardane, M. Shen, E. P. Fisher and J. Poston, Energy Fuels, 2001, 15, 279. 9 T. D. Burchell, R. R. Judkins, M. R. Rogers and A. M. Williams, Carbon, 1997, 35, 1279. 10 M. M. Maroto-Valer, Z. Tang and Y. Zhang, Fuel Process. Technol., 2005, 86, 1487. 11 M. Fr‘ere, G. de Weireld and R. Jadot, J. Porous Mater., 1998, 5, 275. 12 M. Cinke, J. Li, C. W. Bauschlicher Jr., A. Ricca and M. Meyyappan, Chem. Phys. Lett., 2003, 376, 761. 13 G. Guan, T. Kida, T. Ma, K. Kimura, E. Abe and A. Yoshida, Green Chem., 2003, 5, 630. 14 J. Baltrusaitis, J. H. Jensen and V. H. Grassian, J. Phys. Chem. B, 2006, 110, 12005. 15 A. K. Mishra and S. Ramaprabhu, J. Phys. Chem. C, 2010, 114, 2583. 16 Z. Shu and S. Wang, J. Nanomater., 2009, 2009, 340217.
This journal is ª The Royal Society of Chemistry 2011
17 T. Missana, C. Maffiotte and M. Garcıa-Gutierrez, J. Colloid Interface Sci., 2003, 261, 154. 18 Q. Weizhon, T. Liu, F. Wei, Z. Whang, G. Luo, H. Yu and Z. Li, Carbon, 2003, 41, 2613. 19 U. J. Kim, C. A. Furtado, X. Liu, G. Chen and P. C. Eklund, J. Am. Chem. Soc., 2005, 127, 15437. 20 S. Tiwari, D. M. Phase and R. J. Choudhary, Appl. Phys. Lett., 2008, 93, 234108. 21 S. Tiwari, R. Prakash, R. J. Choudhary and D. M. Phase, J. Phys. D: Appl. Phys., 2007, 40, 4943. 22 S. G. Kazarian, M. F. Vincent, F. V. Bright, C. L. Liotta and C. A. Eckert, J. Am. Chem. Soc., 1996, 118, 1729. 23 S. Cavenati, C. A. Grande and A. E. Rodrigues, J. Chem. Eng. Data, 2004, 49, 1095. 24 Z. Zhang, M. Xu, H. Wang and Z. Li, Chem. Eng. J., 2010, 160, 571. 25 A. R. Millward and O. M. Yaghi, J. Am. Chem. Soc., 2005, 127, 17998. 26 Y. Belmabkhout, R. S. Guerrero and A. Sayari, Chem. Eng. Sci., 2009, 64, 3721. 27 M. M. Dubinin and L. V. Redushkevitch, Zh. Fiz. Khim., 1947, 21, 1351. 28 M. Polanyi, Verhandt. Deut. Phys. Ges., 1914, 16, 1012. 29 M. R. Nelson and R. F. Borkman, J. Phys. Chem. A, 1998, 102, 7860. 30 M. M. Shaijumon and S. Ramaprabhu, Chem. Phys. Lett., 2003, 374, 513. 31 J. F. Liu, Z. S. Zhao and G. B. Jiang, Environ. Sci. Technol., 2008, 42, 6949.
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