Browsing by Author "Wang, T. T."

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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
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Lin, Cheng-Kuo
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Wang, T. T.
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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 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
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Chuang, Chung-Ching
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Raghunath, Putikam
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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.
Synergistic Effect of Hydrogenation and Thiocyanate Treatments on Ag-Loaded TiO2 Nanoparticles for Solar-to-Hydrogen Conversion
(2017-05-11)
Wang, T. T.
;
Raghunath, P.
;
Lin, Y. G.
;
Lin, M. C.
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應用化學系分子科學碩博班
H-2 evolution rate enhanced by Ag-loading on 25 nm TiO2 anatase nanopatticles (denoted as Ag/TiO2), Ag-loaded on hydrogenated TiO2 NPs (Ag/H:TiO2), as well as by the treatment of both NPs with potassium thiocyanate (KSCN) solution have been systematically investigated in conjunction with quantum-chemical-calculations and XANES and EXAFS analyses with synchrotron radiation. We have observed a cumulative enhancement effect of these fabrication processes on solar to;hydrogen A To(STH) conversion using a. simulating light source, Ag/TiO2 shows an enhanced visible absorption with 4-5 tiine increase in H-2 evolutioh over that of TiO2 or H:TiO2 prepared under mild hydrogenation conditions, while Ag/H:TiO2 exhibits an even greater UV visible absorption, similar to that of Ag/H:TiO2 with 3.1 times higher STH than that of Ag/TiO2. The treatment of Ag/TiO2 and Ag/H:TiO2 NPs With 0.1 mM KSCN solution, further increases:their STHs by 3.6 and 2.8 times, respectively. Optimization of KSCN concentration up to 02 mM gave [H-2] production rate rise to 2.75 mmol h(-1) g(-1) under Xe lamp illumination for the AgSCN/H:TiO2 system, which has also been tested for its durability, showing a notable robustness. The observed synergistic effect of TiO2 hydrogenation and SCN treatment of the Ag/H:TiO2 NPs has been corroborated by the results of quantum chemical elucidation of H2 production mechanism and the photocatalytic effects of Ag/H:TiO2 and AgSCN/H:TiO2 NPs revealed by appearances of new sub-band states within the TiO2 bandgap, as well as by the result of XANES and EXAFS analyses which support the electron pulling effect of the SCN group attached to Ag. Finally, we have also compared the efficacies of H-2, HCOOH, and CH3OH as hydrogenation sources at 300 degrees C and the efficacies of CH3OH, C2H5OH, and sucrose as sacrificial agent to facilitate the separation of the electron from the hole.