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Nongnual T.,Laboratory for Computational and Applied Chemistry | Nongnual T.,Kasetsart University | Nokbin S.,Laboratory for Computational and Applied Chemistry | Nokbin S.,Kasetsart University | And 5 more authors.
Carbon | Year: 2010

The electron hopping mechanism in the single-walled carbon nanotube (SWCNT)-mediated redox reaction between anthraquinonyl (AQH2) and 4-arylhydroxyl amine (4AHA) groups is studied by density functional theory calculations. The (8, 0) SWCNT is used to mimic the real system of interest. It is found that electrons from the oxidized AQH2 group can be transferred to the oxidizing 4AHA group, at the other end of the nanotube, by a hopping process through the mediating SWCNT. Disparity of electron densities ascribable to non-localized electrons confirms this finding. The disparity, partial electron density difference, and Hirshfeld partial charges analyses show that the SWCNT can hold 87% of the extra electron density of the hypothetical negative intermediate produced from the oxidation of the AQH2 process. Chemical attachments of these two redox reagents to the SWCNT also cause new impurity states within the band gap, thereby giving more metallic characteristics to the system. These findings provide a detailed understanding of the electron hopping process and agree well with a previous experimental study. © 2009 Elsevier Ltd. All rights reserved. Source

Krainara N.,Laboratory for Computational and Applied Chemistry | Krainara N.,Kasetsart University | Nokbin S.,Laboratory for Computational and Applied Chemistry | Nokbin S.,Kasetsart University | And 5 more authors.
Carbon | Year: 2010

The attachment of a variety of nitrogen nucleophilic groups to BN-doped single wall carbon nanotubes (SWCNTs) was characterized by quantum mechanical calculations at the DFT-level. We found that the binding energies for all systems lie between -6.90 and -30.13 kcal/mol and are in the order guanidine > arginine > ammonia > imidazole > chitosan > pyridine > m-nitroaniline, which is analogous to the pKa. m-Nitroaniline and pyridine grafted tubes display a smaller energy gap, 0.252 and 0.347 eV, respectively, compared to an isolated BN-doped SWCNT, 0.430 eV. For the other cases, the energy gaps did not change significantly, which is in keeping with the results for the densities of states (DOS). In the cases of m-nitroaniline and pyridine, electron density is seen at the Fermi level of both SWCNTs and probe molecules when the DOS is split into these two contributions, different from the isolated probe molecules. Thus, m-nitroaniline and pyridine attached to BN-doped SWCNTs increase the conductivity of the system. © 2009 Elsevier Ltd. All rights reserved. Source

Kongpatpanich K.,Laboratory for Computational and Applied Chemistry | Kongpatpanich K.,Kasetsart University | Nanok T.,Laboratory for Computational and Applied Chemistry | Nanok T.,Kasetsart University | And 4 more authors.
Physical Chemistry Chemical Physics | Year: 2011

The initial stage of glycerol conversion over H-ZSM-5 zeolite has been investigated using density functional theory (DFT) calculations on an embedded cluster model consisting of 128 tetrahedrally coordinated atoms. It is found that glycerol dehydration to acrolein and acetol proceeds favourably via a stepwise mechanism. The formation of an alkoxide species upon the first dehydration requires the highest activation energy (42.5 kcal mol-1) and can be considered as the rate determining step of the reaction. The intrinsic activation energies for the first dehydration are virtually the same for both acrolein and acetol formation, respectively, suggesting the competitive removal of the primary and secondary OH groups. A high selectivity to acrolein at moderate temperatures can be attributed to the selective activation of the stronger adsorption mode of glycerol through the secondary OH group and the kinetically favoured subsequent consecutive steps. In addition, the less reactive nature of acrolein relative to acetol precludes it from being converted to other products upon conversion to glycerol. In accordance with typical endothermic reactions, the forward rate constant for glycerol dehydration significantly increases with increasing reaction temperature. © 2011 the Owner Societies. Source

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