Hydrothermal Synthesis Of Monoclinic WO₃ And Its Photocatalytic Performance

The monoclinic WO₃ as a photocatalytic material for hydrogen production from decomposition of water exhibited better activity.In this work,monoclinic WO₃ was successfully synthesized by the hydrothermal method using sodium tungstate as tungsten source,nitric acid as acid source,and hydroxyl acids including citric acid,tartaric acid and malic acid as surfactant.We explored the suitable conditions for monoclinic WO₃synthesized with regular morphology by directly controlling the hydrothermal conditions.X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,and ultraviolet-visible diffuse reflectance?UV-Vis DR?were employed to characterize the synthesized WO₃.The effects of type of acid source,the molar ratios of hydroxyl acids to tungsten atoms,as well as hydrothermal temperature and time on crystal phases and morphologies of WO₃ were investigated in detail.The results indicated that,morphology-ordered and monoclinic WO₃ was achieved under suitable conditions of molar ratios of nitric acid to tungsten atom of 2.8:1,hydroxyl acids to tungsten atom of 0.8:1,a hydrothermal temperature of 190?,as well as hydrothermal time of 16 h.In addition,platelet morphology of WO₃ was prepared in presence of citric acid or malic acid as an adjuvant.However,the morphology became square block in presence of tartaric acid as adjuvant.The WO₃ with n-type conductivity properties was coupled with p-type semiconductor CuCrO₂ to fabricate the CuCrO₂-WO₃ composite photocatalyst.The photocatalytic performance of the synthesized WO₃ was evaluated by testing the photocatalytic activity of corresponding CuCrO₂-WO₃ in the photocatalytic decomposition of pure water.The effects of the concentration of sodium tungstate,the amount of hydroxyl acid,the type and amount of inorganic salt,and the heat treatment conditions of the synthesized samples on photocatalytic properties of WO₃ were investigated in detail.The results indicated that,the monoclinic WO₃ with high crystalline perfection and small average particle size was obtained under suitable conditions of the concentration of sodium tungstate was 0.10 mol/L,the molar ratio of hydroxyl acid to tungsten atom was 0.8:1,and the molar ratio of sodium nitrate to tungsten atoms was 0.2:1,as well as first calcination at 500?for 2 h and then calcination at 650?for 1.5 h in air atmosphere.The corresponding CuCrO₂-WO₃exhibited highest photocatalytic properties.The hydrogen production was 167.1?mol under the irradiation of 250 W mercury lamp for 1 h.We investigated the stability of CuCrO₂-WO₃,the photocatalytic activity test was conducted under the irradiation of 250 W mercury lamp.The results indicated that the H₂production remained at a stable state with an average activity of 161.4?mol/h.As the same,the photocatalytic activity remained unchanged under the irradiation of 300W xenon lamp.An average activity was 2.2?mol/h.