The fabrication and photoelectrocatalytic study of composite ZnSe/Au/TiO2 nanotube films

In this paper, anatase TiO2 nanotube (NT) film photoelectrodes are successfully fabricated by a simple and effective hydrothermal method. Subsequently, an aqueous-phase processing technique is adopted to construct highly dispersed ZnSe quantum dots (QDs) on Au/TiO2 NT films prepared by microwave-assisted chemical reduction, which formed composite ZnSe/Au/TiO2 NT film systems (ZATs) with excellent performance in photoelectrocatalytic (PEC) applications. The morphology and performance of as-obtained ZATs were investigated based on various characterizations. The investigation revealed that as-obtained ZATs not only greatly extend spatial separation of charges and restrain the recombination rate of photogenerated electron-hole pairs, but also improve the efficiency to use visible light and display a wide and strong absorption in the visible light region ranging from 400 nm to 800 nm. Moreover, we observe a larger fluorescence quenching of ZATs compared with that of pure TiO2 NT films and binary composites. Experimental results indicate that the photocurrent densities of pure TiO2, 0.8 Au/TiO2, 60 min ZnSe/TiO2, and ZATs are 0.020 mA cm−2, 0.032 mA cm−2, 0.037 mA cm−2 and 0.070 mA cm−2, respectively, which is approximately 2-3.5 times higher than that of pure TiO2 NT films and binary compound photoelectrodes. Additionally, experimental results suggest that the as-prepared ZATs photoelectrode has exhibited considerable stability and significantly increased PEC activity for the degradation of methylene blue (MB) in distilled water under 100 mW cm−2 xenon lamp irradiation. The degradation efficiency on MB of 45 min ZnSe/0.8 Au/TiO2 NT films approaches 91%; however, the counterpart of TiO2 NT films is less than 10%. Eventually, the mechanism for the improvement of the PEC performance of ZATs is discussed to point out that ZATs display prominent charges transport performance, and a stepwise band alignment structure is built up in its photoelectrode, which indicates that charge separation and migration across the interfaces should favor vectorial electron transfer according to the scheme of ZnSe → TiO2 → Au → Ti substrates.