Browsing by Author "Srinivasadesikan, V."

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Computational and experimental studies on the effect of hydrogenation of Ni-doped TiO2 anatase nanoparticles for the application of water splitting
(2015-01-01)
Chuang, Chung-Ching
;
Lin, Cheng-Kuo
;
Wang, T. T.
;
Srinivasadesikan, V.
;
Raghunath, P.
We have studied theoretically and experimentally the effect of Ni-doping in TiO2 nanoparticles (NPs) on hydrogenation. The doped NPs can be hydrogenated readily in a much shorter time at T < 623 K under near atmospheric H-2 pressure. The hydrogenated black NP films exhibit a broad UV-Vis absorption extending well beyond 800 nm. The experimental data can be corroborated by quantum calculations. The barriers for dissociative adsorption of H-2 at the Ni and O-2c sites on the 2Ni-doped TiO2 surface are significantly reduced from 48 kcal mol(-1) on the undoped surface to 17 and 12 kcal mol(-1), respectively. The computed densities of states of the doped TiO2 also show new absorption peaks in the band-gaps of the hydrogenated systems which exhibit a high efficiency of solar water-splitting over those of nonhydrogenated samples based on our preliminary study. The theoretical result also indicates that Ni-doping significantly affects the enthalpies of hydrogenation for formation of 2HO(b) and H2O(b) in the bulk from 7 and 19 kcal mol(-1) in the undoped TiO2 to -76 and -69 kcal mol(-1) in the 2Ni-TiO2 system, respectively, with a > 80 kcal mol(-1) increase in exothermicities.
Quantum chemical investigation on the role of Li adsorbed on anatase (101) surface nano-materials on the storage of molecular hydrogen
(2015-06-01)
Srinivasadesikan, V.
;
Raghunath, P.
;
Lin, M. C.
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應用化學系
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Department of Applied Chemistry
Lithiation of TiO2 has been shown to enhance the storage of hydrogen up to 5.6 wt% (Hu et al. J Am Chem Soc 128: 11740-11741, 2006). The mechanism for the process is still unknown. In this work we have carried out a study on the adsorption and diffusion of Li atoms on the surface and migration into subsurface layers of anatase (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT+U). The model consists of 24 [TiO2] units with 11.097x7.655 angstrom(2) surface area. Adsorption energies have been calculated for different Li atoms (1-14) on the surface. A maximumof 13 Li atoms can be accommodated on the surface at two bridged O, Ti-O, and Ti atom adsorption sites, with 83 kcal mol(-1) adsorption energy for a single Li atom adsorbed between two bridged O atoms from where it can migrate into the subsurface layer with 27 kcal mol(-1) energy barrier. The predicted adsorption energies for H-2 on the lithiated TiO2 (101) surface with 1-10 Li atoms revealed that the highest adsorption energies occurred on 1-Li, 5-Li, and 9-Li surfaces with 3.5, 4.4, and 7.6 kcal mol(-1), respectively. The values decrease rapidly with additional H-2 co-adsorbed on the lithiated surfaces; the maximum H-2 adsorption on the 9LiTiO(2)(a) surface was estimated to be only 0.32 wt% under 100 atm H-2 pressure at 77 K. The result of Bader charge analysis indicated that the reduction of Ti occurred depending on the Li atoms covered on the TiO2 surface.
Quantum-chemical prediction of the effects of Ni-loading on the hydrogenation and water-splitting efficiency of TiO2 nanoparticles with an experimental test
(2017-01)
Lin, Cheng-Kuo
;
Chuang, Chung-Ching
;
Raghunath, Putikam
;
Srinivasadesikan, V.
;
Wang, T. T.
The effects of Ni-loading on TiO2 nanoparticles can pronouncedly reduce the barriers for dissociation of H-2 from 48 kcal/mol on the pure TiO2 to as low as 1-3 kcal/mol on the loaded samples facilitating the hydrogenation of NPs. Preliminary data of our test indicate that the hydrogenation of Ni-loaded TiO2 NPs results in a significant UV-visible absorption extending well beyond 750 nm with an increase in water splitting efficiency by as much as 67 times over those of pure and hydrogenated TiO2 NPs without Ni-loading under our mild hydrogenation condition using 800 Torr of H-2 at 300 degrees C for 3 h. (C) 2016 Elsevier B.V. All rights reserved.