The visible-light-driven type III heterojunction H₃PW₁₂O₄₀/TiO₂-In₂S₃: A photocatalysis composite with enhanced photocatalytic activity

H₃PW₁₂O₄₀/TiO₂-In₂S₃, a visible-light-driven Type III photocatalysis composite heterojunction, is synthesized by typical sol-gel method. The X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectrometer (ICP-AES) and energy dispersive X-ray spectra (EDS) analysis show that HPW which is anchored to the surface of TiO₂-In₂S₃makes the crystallite sizes of HPW/TiO₂-In₂S₃reduce to 9.7 nm. X-ray photoelectron spectroscopy (XPS) analysis confirm that HPW acts as the bridge assisting in the transfer of electronics from TiO₂to In₂S₃in H₃PW₁₂O₄₀/TiO₂-In₂S₃. The optical properties of synthesized composites are investigated by UV–Vis diffused reflection spectra (UV–Vis DRS) and photoluminescence (PL) spectra. The lattice defects of TiO₂lead to the existence of oxygen-vacancies and impurity energy levels which make TiO₂respond to visible light. And the type-III heterojunction restrains the recombination of photo-generated carriers effectively. Under visible light irradiation (λ = 400 nm), H₃PW₁₂O₄₀/TiO₂-In₂S₃displays higher photocatalytic degradation activity of imidacloprid (82.7%), comparing with H₃PW₁₂O₄₀/TiO₂(26.7%), TiO₂-In₂S₃(20.6%) and TiO₂(16.0%). The pseudo-first-order degradation rate constant of HPW/TiO₂-In₂S₃is 6, 7 and 13 times higher than that of HPW/TiO₂, TiO₂-In₂S₃and TiO₂, respectively. Moreover, the photogenerated holes and ·OH radicals are proved as the main active species in degradation process.