565 research outputs found
Pore structure and graphitic surface nature of ordered mesoporous carbons probed by low-pressure nitrogen adsorption
No full textOrdered mesoporous carbons (OMCs) were produced by pyrolysis of sucrose adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in hydrofluoric acid. Subsequently, some of these OMCs were heat-treated at temperatures of up to 1600 degreesC. The ONIC pore structure was studied by low-pressure nitrogen adsorption. Information on the graphitic order of the surface of the mesopore walls was also obtained from the nitrogen adsorption data. These results were correlated to the order of the graphene layers at the outer surface, which was studied by X-ray photoelectron spectroscopy (XPS). The OMCs were predominantly mesoporous, but they also contained micropores. For OMCs produced in an SBA- 15 matrix, the micropore volume decreased upon heating. After heating to 1600 degreesC, nearly all micropores had disappeared. Furthermore, upon heating the width of the mesopores increased from 35 to 50 Angstrom. All these changes can be explained by a shrinking of the OMC framework upon heating. A different behavior was found for OMCs derived from MCM-48. Upon heating these materials at increasingly high temperatures, the width of the mesopores first decreased, and for temperatures above 1100 degreesC it increased again. For all OMCs studied the graphitic order of the mesopores and the order of the graphene layers at the outer surface increased upon heating. For a given temperature, the graphitic surface order of OMCs derived from SBA-15 and MCM-48 was similar. (C) 2003 Elsevier Science Inc. All rights reserved.The authors are thankful to Dr. Annette
Schwerdtfeger for reviewing the manuscript. R. Ryoo gratefully acknowledges that this work was supported in part by the Korean Ministry of Science and Technology through the Creative Research Initiative Program, and by the School of Molecular Science through the Brain Korea 21 Project
Surface chemistry of ordered mesoporous carbons
No full textOrdered mesoporous carbons (OMC) were produced by pyrolysis of hydrocarbons adsorbed in two different silica matrices (MCM-48 and SBA-15), followed by dissolution of the matrix in either hydrofluoric acid or sodium hydroxide. Some carbons were subsequently heat treated at temperatures of up to 1600 degreesC. The chemistry of the external surface was studied by X-ray photoelectron spectroscopy (XPS) and static secondary ion mass spectroscopy (SIMS). Information on the graphitic order of the surface of the mesopores was obtained from low-pressure nitrogen adsorption data. The external and internal surface of the OMC has a polyaromatic, graphite-like character. This character increases considerably with increasing pyrolysis and/or post-pyrolysis temperature, as expected. According to the XPS and the nitrogen adsorption data, this increase was especially pronounced for temperatures above 1100 degreesC. In spite of the different pore structures, only small differences in the polyaromatic character were found for OMC synthesised either in a MCM-48 or in a SBA-15 matrix. Differences exist for the non-carbon elements. When hydrofluoric acid is used for dissolution of the silica matrix, organic fluorine compounds are formed. Their concentration is higher when a MCM-48 matrix as opposed to a SBA-15 matrix was used. Dissolution of the silica matrix in sodium hydroxide yielded a less contaminated OMC as compared to dissolution in hydrofluoric acid. (C) 2002 Elsevier Science Ltd. All rights reserved.The authors are thankful to Dr. Alain Adnot for helpful discussion of the surface spectroscopy results and to Dr. Annette Schwerdtfeger for reviewing the manuscript. R.Ryoo gratefully acknowledges that this work was supported in part by the Korean Ministry of Science and Technology through the Creative Research Initiative Program,
and by the School of Molecular Science through the Brain Korea 21 Project
Surface and pore structures of CMK-5 ordered mesoporous carbons by adsorption and surface spectroscopy
No full textOrdered mesoporous carbons (OMCs) were synthesized in the pore system of SBA-15 aluminosilicates with different Si/Al ratios ranging from 5 to 80. Nitrogen adsorption was used to characterize the pore structure of the aluminosilicates and of the OMCs, whereas the OMC surface chemistry was studied by X-ray photoelectron spectroscopy and static secondary ion mass spectroscopy. The results indicate that the physicochemical properties of the OMCs depended significantly on the acid catalytic activity of the aluminosilicate frameworks, which comes along with the variation of Si/Al ratios. The OMC pore widths and order of the graphene layers followed the same trend as the catalytic activity of the aluminosilicates, whereas the concentration of extraframework species in the aluminosilicates indirectly influenced the mechanical properties of the OMCs. The reasons for this behavior are discussed
Synthesis of ordered mesoporous carbon molecular sieves CMK-1
No full textHighly ordered mesoporous carbon molecular sieves designated as CMK-1 were synthesized using mesoporous MCM-48 silica with various pore diameters as templates. sucrose as a carbon source and sulfuric acid as the carbonization catalyst. The effect of the sucrose-to-sulfuric acid ratio on the structure of the resultant carbon, the effect of the pyrolysis temperature, and the optimum amounts of sucrose for MCM-48 with various pore diameters have been investigated. These results show that the synthesis method can be accurately controlled to obtain the highly ordered mesoporous carbon molecular sieves in a large scale. (C) 2001 Elsevier Science B.V. All rights reserved.This work was supported by KOSEF
Zeolite-templated nanoporous carbon for high-performance supercapacitors
No full textHierarchical porous carbon prepared with calcium-containing nanocrystalline beta zeolite as the template and ethylene as the carbon source at a relatively low carbonization temperature (600 degrees C) displayed excellent electrocapacitive properties. The presence of both micro/mesopores and surface oxygencontaining groups on the ordered porous structure, along with a high specific surface area (2280 m(2) g(-1)) and pore volume (1.95 cm(3) g(-1) ) coupled with good wettability towards the electrolyte enabled the carbon to perform well as a supercapacitor electrode. This carbon electrode achieved a specific capacitance of 250 F g(-1) at a current density of 1 A g(-1) with 1 M H2SO4 as the aqueous electrolyte measured in a three-electrode system. A symmetric capacitor fabricated with the carbon as both electrodes exhibited a specific capacitance of 161 F g(-1 )at a current density of 1 A g(-1), and an excellent cycling stability. After being cycled 17 000 times and shelved for another two months, the electrode exhibited a specific capacitance of 246 F g(-1) at 1 Ag-1, 153% of the initial capacitance, and still maintained an excellent cycle stability. Besides, an all-solid-state supercapacitor cell fabricated with this carbon as both electrodes and polyvinyl alcohol/H2SO4 gel as the electrolyte displayed an areal specific capacitance of 413 mF cm(-2) at a current density of 0.25 mA cm(-2)
Direct observation of 3D mesoporous structure by scanning electron microscopy (SEM): SBA-15 silica and CMK-5 carbon
No full textThe authors are grateful to Messrs Makoto Watanabe (Hitachi Science System) and Yasushi Nakaizumi (Hitachi High-Technologies Corporation) for taking scanning electron micrographs. S.C. thanks Dr. M. Yudasaka (ICORP-JST) for giving advise and comments
Carlitz's Type Twisted (h, q)-Tangent Numbers and Polynomials
No full textAbstract In this paper we define the Carlitz's type twisted (h, q)-tangent numbers
Ryoo, A Note on the q-Euler Numbers and Polynomials with Weak Weight α
No full textWe construct a new type of q-Euler numbers and polynomials with weak weight α :
Zeros of Analytic Continued q-Euler Polynomials and q-Euler Zeta Function
No full textWe study that the q-Euler numbers En,q and q-Euler polynomials En,q(x) are analytic continued to Eq(s) and Eq(s,w). We investigate the new concept of dynamics of the zeros of analytic continued polynomials. Finally, we observe an interesting phenomenon of ‘‘scattering’’ of the zeros of Eq(s,w)
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