Hexagonal phase WO3 nanorods: Hydrothermal preparation, formation mechanism and its photocatalytic O2 production under visible-light irradiation

WO3 with various morphologies and crystal phases were prepared via a hydrothermal process in the presence of different Na2SO4 concentrations. Experimental results indicated that the preferred growth face ((200) crystal plane) of hexagonal WO3 could adsorb abundant Na+, which induced the WO3 growing along [001] crystal direction to form nanorods, and hexagonal phase WO3 nanorods with diameter of 30–150 nm and length of 0.5–5 μm were obtained in the presence of 0.25 M Na2SO4, while excessive Na2SO4 led to a mixed crystal consisting of cubic H2W2O7 and hexagonal WO3. The photoactivities for O2 evolution for various products were investigated by using Fe(NO3)3 as a sacrificial reagent under visible-light irradiation, and the hexagonal phase WO3 nanorods show a better photoactivity than the other products with different morphologies and crystal phases due to its fast three-dimensional photogenerated carrier transfer along its special rod-shaped structure.