Enhanced solar absorption of gold plasmon assisted TiO2-based water splitting composite

Abstract

We report on the effect of thermal annealing on the microstructure, optical properties and wettability of TiO2-based water-splitting (WS) composite using full solar spectrum as source of energy. The WS material used in this study is composed of three layers (SiO2, Al2O3 and TiO2) on top of which a distribution of Localized Surface Plasmon Resonance structures such as gold are formed to obtain a multilayer composite material. The fabricated samples are then annealed at 450−1100°C temperatures range under atmospheric conditions. The crystal structure and chemical composition are determined using X-ray Diffractometer, Scanning Electron Microscope, Energy Dispersive Spectroscopy, High Resolution Scanning and Transmission Electron Microscope. UV–Vis spectroscopy is used to study the influence of thermal annealing on optical absorption. Besides, wettability alteration is assessed using both in-situ (Environmental Scanning Electron Microscope) and ex-situ (sessile drop technique). Our findings reveal that thermal annealing leads to the transformation of amorphous TiO2 to its more stable phase anatase. This transformation enhances significantly the optical properties and increases the hydrophilicity of the material surface making it suitable for WS activity. More importantly, the presence of plasmonic nanostructures allow the material to extend its photoactivity from UV region to full solar spectrum. The gold nanocrystals were also found to prefer the <111> orientation during their evolving and growth after thermal annealing. This specific compact orientation is also reported to increase the efficiency of WS.