Preparation Of Bismuth Oxide/Titanium Dioxidenanotube Arrays Thin Filmsand Their Visible-light Photocatalytic Activity

In recent years, the water pollution is more and more serious and semiconductorphotocatalytic degradation technology for treatment of low concentration, persistentorganic pollutants provides an effective way. TiO2, as the most widely studiedphotocatalyst, has two major limitations, namely the low utilization of sunlight and therecombination of photogenerated electron/holes. Therefore, the modification of TiO2and development of novel visible-light responsive semiconductor photocatalysts havebecome a hot research topic. Bi2O3, with narrow energy gap, can rapidly response undersunlight and owns strong oxidation capability, which is an ideal visible-lightphotocatalyst. Composite photocatalyst with high visible-light photocatalytic activitycan be obtained by assembling TiO2with visible-light responsive Bi2O3.In this paper, two-step anodic oxidation method was used to construct the highlyordered TiO2nanotube arrays (hereinafter referred to as TNTAs) thin film. The effectsof experimental parameters including the content of H2O, secondary oxidation time andthe temperature of heat treatment on the structure and photocatalytic properties werestudied and the optimized preparation conditions were determined, that is3vol%H2O,secondary oxidation time of2h and heat treatment temperature of550℃. The sol-gelmethod was used to prepare Bi2O3and the effects of HNO3and PEG200on themicrostructure and phtocatalytic activity were discussed. The optimized preparationconditions were3.2mL HNO3and3.5mL PEG200.With TNTAs as substrate, the impregnation-decomposition method was used toassemble Bi2O3in order to synthesize Bi2O3/TNTAs thin film. The affects of Bi2O3colloid concentration, vacuum degree and heat treatment temperature on the filmmorphology and photocatalytic performance were studied to optimize the preparationconditions. SEM, XRD, XPS and UV-Vis were applied to characterize the structure andproperties of the Bi2O3/TNTAs thin film. The inner relationship of the microstructure,solar spectrum matching and photocatalytic performance was investigated. Finally, apossible ptotocatalytic mechanism was discussed in detail, too. The results showed thatBi2O3and TiO2were two main phases in the Bi2O3/TNTAs thin film and the two phaseswere not just a simple composition, but chemical reactions happened between them togenerate a new phase, i.e. Bi4Ti3O12. The optical absorption threshold of the compositefilm increased from420nm to515nm and the band gap decreased from2.96eV to2.40eV after assembling TNTAs with Bi2O3. The visible-light photocatalytic results showedthat the degrading efficiency of Bi2O3/TNTAs thin film (93.5%) was obviouslyenhanced compared with pure TNTAs (23.0%). The photocatalytic reaction kinetics analysis displayed that the photocatalytic reactions were pseudo-first order reaction andthe reaction rate of Bi2O3/TNTAs film was16times as that of TNTAs. In themechanism analysis, the improvement of the visible-light photocatalytic performancecan be mainly attributed to the effective assembly of TiO2with Bi2O3and the existenceof Bi4Ti3O12phase, which resulted in enhanced absorption and utilization of visible lightand high separation efficiency ofphotogenerated carriers.