H₃PW₁₂O₄₀/TiO₂-In₂O₃: A visible light driven type-II heterojunction photocatalyst for the photocatalytic degradation of imidacloprid

H₃PW₁₂O₄₀/TiO₂-In₂O₃, a type-II heterojunction photocatalyst with ternary composite structure, was synthesized by a sol-gel method. The structure, composition and morphology of H₃PW₁₂O₄₀/TiO₂-In₂O₃ were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). UV-Vis diffused reflection spectroscopy (UV-Vis DRS) and photoluminescence spectroscopy (PL) were applied to investigate the optical properties of the catalysts synthesized. In addition, the photocatalytic activity of the catalysts were tested via degradation of imidacloprid under visible light (λ ≥ 400 nm). The results indicated that the introduction of H₃PW₁₂O₄₀ and In₂O₃ brought lattice defects into the TiO₂ substrate. This led to introduction of oxygen-vacancies and impurity energy levels, which meant that TiO₂ could respond to visible light. The superiority of the type-II heterojunction and ternary composite structure was highlighted by the decrease in the photoluminescence intensity (85%) and the favorable photocatalytic activity (degradation efficiency of 83%). The enhanced photocatalytic activity of H₃PW₁₂O₄₀/TiO₂-In₂O₃ was ascribed to the separation of the photo-generated carriers via the type-II heterojunction and the suppression of recombination via the ternary composite structure. Moreover, the main active species of the degradation process were proven to be holes and OH.