The synergistic effect of phase heterojunction and surface heterojunction to improve photocatalytic activity of V_O^•–TiO₂: the co-catalytic effect of H₃PW₁₂O₄₀

With nanotube titanic acid (abbreviated as NTA) and the 12-tungstophosphoric acid (H₃PW₁₂O₄₀•xH₂O, denoted as HPW) as start materials, respectively, according to a simple hydrothermal process in acid medium, we successfully prepared HPW modified V_O^•–TiO₂ composite photocatalysts. During heat treatment companied by the transformation of NTA to TiO₂, a kind of single-electron-trapped oxygen vacancy (V_O^•) could be formed contributing to the visible light absorption of catalysts. The morphology, phase and chemical structure, optical and electronic properties, and so on of the produced catalysts with various HPW loadings are characterized. The size range of synthesized photocatalyst nanoparticles are about 10~50 nm. Taking aqueous rhodamine B (RhB) dye as model pollutant, we carried out photocatalytic activity test of the achieved catalysts, revealing that the hybrid photocatalysts display significantly enhanced visible light-driven (#lambda# ≥ 420 nm) photocatalytic activity for degradation of RhB. Among various catalysts, HPWN-0.1-120 composite with nominal loading of 0.1 g HPW and heat treatment temperature of 120 °C possesses the highest photocatalytic performance in visible light, which is closely related to the co-effect of phase heterojunction of rutile/anatase, surface heterojunction of anatase/HPW, and oxygen vacancy (V_O^•). The two types of heterojunction promote greatly the separation efficiency of photoelectrons and photoholes and oxygen vacancy lures response of catalysts to visible light.