Browsing by Author "Liu, Wei-szu"

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Is surface doping or bulk doping more beneficial to the photocatalytic activity of TiO2?
(2013-09-08)
Chang, Sue-min
;
Liu, Wei-szu
;
環境工程研究所
;
Institute of Environmental Engineering
Surface doping is more beneficial than bulk doping to the photocatalytic activity of vanadium-doped TiO(2)
(2011-01-14)
Chang, Sue-min
;
Liu, Wei-szu
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, we examined the effects of surface and bulk doping on the photocatalytic activity of vanadium (V)-doped TiO(2) on the basis of charge trapping, separation, and interfacial transfer. Moreover, we characterized the microstructures and electronic structures of the two types of doped TiO(2) and the chemical states of the doped V ions to elucidate the causes of the different physicochemical properties. The photocatalytic activity of the doped TiO(2) was enhanced by 1.9 times when the V ions were doped only in the surface lattice at a surface V/Ti molar ratio of 3.0 x 10(-1), in contrast, bulk doping caused detrimental effects. Reduced species, including V(3+) and V(4+) ions, were formed in the interstitial anatase lattice. These impurities introduced occupied and unoccupied energy levels, which were close to and in the conduction band of TiO(2), respectively. The V(3+)/V(4+) ions within the TiO(2) lattice inhibited charge diffusion to the surface through deep trapping. In contrast, the impurities present only in the surface lattice increased the number of surface trapped holes and facilitated the interfacial charge transfer from the photoactivated TiO(2) to adsorbates. Heavy doping at the surface resulted in the formation of V(2)O(5). The p-n junction between the TiO(2) and V(2)O(5) separated charge carriers and additionally promoted the photocatalytic activity of the surface-doped TiO(2). (c) 2010 Elsevier B.V. All rights reserved.
Surface doping is more beneficial than bulk doping to the photocatalytic activity of vanadium-doped TiO2
(2011-01-14)
Chang, Sue-min
;
Liu, Wei-szu
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, we examined the effects of surface and bulk doping on the photocatalytic activity of vanadium (V)-doped TiO2 on the basis of charge trapping, separation, and interfacial transfer. Moreover, we characterized the microstructures and electronic structures of the two types of doped TiO2 and the chemical states of the doped V ions to elucidate the causes of the different physicochemical properties. The photocatalytic activity of the doped TiO2 was enhanced by 1.9 times when the V ions were doped only in the surface lattice at a surface V/Ti molar ratio of 3.0 x 10(-1), in contrast, bulk doping caused detrimental effects. Reduced species, including V3+ and V4+ ions, were formed in the interstitial anatase lattice. These impurities introduced occupied and unoccupied energy levels, which were close to and in the conduction band of TiO2, respectively. The V3+/V4+ ions within the TiO2 lattice inhibited charge diffusion to the surface through deep trapping. In contrast, the impurities present only in the surface lattice increased the number of surface trapped holes and facilitated the interfacial charge transfer from the photoactivated TiO2 to adsorbates. Heavy doping at the surface resulted in the formation of V2O5. The p-n junction between the TiO2 and V2O5 separated charge carriers and additionally promoted the photocatalytic activity of the surface-doped TiO2. (c) 2010 Elsevier B.V. All rights reserved.
The roles of surface-doped metal ions (V, Mn, Fe, Cu, Ce, and W) in the interfacial behavior of TiO2 photocatalysts
(2014-09-01)
Chang, Sue-min
;
Liu, Wei-szu
;
環境工程研究所
;
Institute of Environmental Engineering
Six types of transition metal ions, including V, Mn, Fe, Cu, Ce, and W, are doped into the surface lattice of TiO2 powders, and their roles in the charge trapping, recombination, interfacial transfer, and photocatalytic activity are systematically studied. The surface-doped TiO2 powders exhibit photocatalytic activity in the order of Fe/TiO2 > Cu/TiO2 > V/TiO2 > W/TiO2 > Ce/TiO2 > Mn/TiO2. While the Fe, Cu and V ions improve the activity, the W, Ce, and Mn ions cause detrimental effects. The different influences are associated with their energy levels, coordination numbers and electronegativity. The surface-doped ions trap charge carriers and interact with adsorbates to provide alternative pathways for interfacial charge transfer. The Fe and Cu ions inhibit defect-mediated annihilation, facilitating interfacial charge transfer in terms of d-d transitions and thermally induced de-trapping. The Mn ions, which introduce both occupied and unoccupied states in the mid-band-gap region, in contrast, trap holes and electrons to severely consume charge carriers via intra-atomic relaxation. The Ce and W ions, which have high coordination numbers and electronegativity, strongly bond the O-2(-) radicals, thus limiting charge utilization as well as photocatalytic performance. (C) 2014 Elsevier B.V. All rights reserved.