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【答案】应助回帖
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220chengeng: 金币+30, 翻译EPI+1, 感谢应助，辛苦了。 2012-12-28 16:40:21
人工翻，见笑了。
This is because the incorporation of the aluminum ions has significantly miniaturized the partical size of ZnO. When the particle size of zinc oxide becomes smaller, the energy gap widens causing the conduction band to be more negative, thus, the valence band becomes more positive resulting in stronger oxidation ability and improves the photocatalytic activity. At the mean time, the particle diameter reduction of nano zinc oxide resulted in the increase of surface area and the related substrate adsorption ability, which could also promote the photocatalytic reaction. Further, from chemical viewpoint, the dopant ions are effective electron acceptor, with ability of capturing the electrons from the conduction band.
Due to the absorption towards electrons by the dopant ions, the combination between the light-generated electrons e- on the semiconductor surface and the photogenerated holes h+ is reduced. Therefore, it generated more 0H • and • O2 on the semiconductor surface, improving the activity of the catalyst. The doping of aluminum ion made it the capture trap for electron and cavity, causing the reduced recombination of electrons and holes as well as the increase of OH • life. When the doping amount is smaller than the optimum doping concentration, as the doping amount increases, the amount of capture traps generated by dopant ions increases, the suppression capability on the recombination between electrons and holes enhanced, so that photocatalytic ability improves. When the dopant amount is greater than the optimum amount, due to the reduction of capture distance between the current carriers, the dopant ions will become the recombination centers for the electrons and holes. Besides, excessive amount of the doping ions also may produce a new phase because of its saturation in the ZnO, which would reduce the effective surface area of the ZnO, and affects the efficiency of the photocatalysis. From the viewpoint of micro-structure and lattice distortion, the incproration of Al3+ in ZnO substrate could be either to substitute metal ion Zn2+, or to exist in the interstitial position between ZnO lattices. Because the ionic radius of aluminum (0.054nm) is smaller than that of zinc (0 .074 nm), it will causee local distortion of the crystal lattice. The energy band structure will change due to the doping by aluminum, i.e. energy gap widens leading to the increasing oxidation capacity of ZnO. Furthermore, since there is a large lattice distortion and strain energy, in order to compensate this energy and distortion, the oxygen on the surface of ZnO can easily escape the lattice and play the role of hole trapping, which also reduces the recombination possibility between electron-hole pairs, thus improving the catalytic activity of ZnO. |
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