Preparation Process Optimization Of Doping Titania Nanowire Arrays And Their Visible-light Photocatalytic Activity

In this paper, the preparation process of porous anodic alumina (PAA) templateand sol-electrophoresis process were optimized on the principle that the visible-lightphotocatalytic activity of titania (TiO₂) nanowire arrays didn't decline. The effects ofmetal ion co-doping, semiconductor doping, semiconductor and metal ion co-dopingon the photocatalytic activity of TiO₂ nanowire arrays were systematically studied.According to the current problems such as the sol we use to prepare TiO₂ nanowireswas synthesized by tetrabutyl titanate costly and the sol itself has no visible-lightphotocatalytic activity, the inexpensive material inorganic titanyl sulfate (TiOSO₄)was used as raw material to synthesize refluxed sol (RS). The RS sol was then used toprepare TiO₂ nanowire arrays by sol-electrophoresis method. The photocatalyticactivity of the as-prepared TiO₂ nanowire arrays was subsequently studied.The pore size of the PAA template prepared respectively by the former processand the new process (anodization processâ… : 1h, anodization processâ…¡: 4h, poreenlarging process: 45min) was identical. The morphology and visible-lightphotocatalytic activity of the nanowire arrays are similar too. When the solelectrophoresistime was controlled between 2.0 min².5 min, the nanowires in thepores of the PAA template could be prepared long enough, and also the TiO₂ filmwouldn't be formed on the surface of PAA template, so the polishing process which isdifficult to control was avoided. Compared with metal ion mono-doped TiO₂, the codopedTiO₂ had higher visible-light photocatalytic activity with further red-shifted ofUV-Vis absorption spectrum and narrowed of band gap. The light utilizationefficiency and photo-quantum efficiency were greatly improved because of thesynergistic effect of the different doped metal ions. But the synergistic effect dependson the doped metal ions. In coupled semiconductor InVO₄/TiO₂, the charge carrierrecombination was effectively inhibited because of the interlaced energy level. So thephotocatalytic activity was greatly improved. However, the photocatalytic activity ofInVO₄ and metal ion co-doped TiO₂ (InVO₄/M/TiO₂) nanowire arrays was no betterthan that of InVO₄/TiO₂.The RS sol prepared by TiOSO₄ was pale yellow, transparent, good fluidity,neutral and stable. The crystalline TiO₂ thin film was prepared by RS sol at low temperature. The crystal was short-rod-like, 30 nm-50 nm in length, and the aspectratio was 2. The crystal phase was anatase according to XRD pattern. The bestelectrophoretic voltage to prepare TiO₂ nanowires by RS sol was 5 V. The pure TiO₂nanowires had very high visible-light photocatalytic activity, the degradation rate ofmethyl orange (MO) was 81.4% after irradiated under visible light for 12 h. The highphotocatalytic activity was ascribed to the visible-light sensitization of peroxo titanicacid. When metal ion or semiconductor was doped in, the absorption band edge wasred shifted further, and the visible-light photocatalytic activity was improved greatly.