Hydrothermal synthesis of monoclinic WO₃ and its photocatalytic hydrogen production performance

Monoclinic WO₃ was successfully synthesized by the hydrothermal method using sodium tungstate as tungsten source, nitric acid as acid source, and citric acid (tartaric acid) as surfactant. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible diffuse reflectance (UV-vis-DR), and Brunner-Emmet-Teller (BET) were employed to characterize the structure and morphology of WO₃. The effects of molar ratios of nitric acid and citric acid (tartaric acid) to tungsten atoms on crystal phases and morphologies of WO₃ were investigated in detail. The results indicated that large amounts of nitric acid and addition of hydroxyl acids were found favorable for the formation of monoclinic WO₃. Monoclinic WO₃ was achieved under suitable conditions of molar ratios of nitric acid to tungsten atom of 2.8:1 and hydroxyl acids to tungsten atom of 0.8:1. The WO₃ was coupled with p-type semiconductor CuCrO₂ to fabricate the CuCrO₂-WO₃ composite photocatalyst. It was used for hydrogen production from photocatalytic decomposition of water. The monoclinic WO₃ with high crystalline perfection exhibited better photocatalytic properties.