Abstract:

A visible light response catalyst with abundant S vacancies, zinc indium sulfide(V_S-ZIS), was prepared in situ by one-step method using thioacetamide as the sulfur source. The process of selective photocatalytic oxidation of 5-hydroxymethylfurfural(HMF) to 2, 5-diformylfuran(DFF) over V_S-ZIS was studied, and the mechanism of V_S-ZIS photocatalytic selective oxidation of HMF to DFF was analyzed. The existence of S vacancies was confirmed by electron paramagnetic resonance(EPR). The optical properties and elemental composition of V_S-ZIS were investigated by UV-vis diffuse reflectance spectroscopy(DRS) and XPS, and the surface morphology and crystal structure of the catalyst were observed using SEM and XRD. The results showed that ZnIn₂S₄ could be successfully synthesized by the one-step method. The catalyst exhibited a petal-like microsphere morphology, and the elements of Zn, In, and S were uniformly distributed. The visible light absorption range of the catalyst was 420-530 nm. The synthesis time did not has significantly effect on the crystal structure of ZnIn₂S₄, while the S vacancies in the catalyst could be controlled by adjusting the synthesis time. Among the samples of V_S-ZIS-2 to V_S-ZIS-10 prepared at 2-10 h, the sample V_S-ZIS-6 obtained at 6 h had abundant S vacancies. The V_S-ZIS-6 prepared by heating at 80 ℃ for 6 h showed the best performance for the selective oxidation of HMF under the conditions of a reaction time of 4 h, V_S-ZIS-6/HMF mass ratio of 3.2, HMF concentration of 1.0 mmol/L, and air flow rate of 20 mL/min. The HMF conversion rate reached 95.4%, and the DFF yield was 61.8%. The abundant S vacancies on the surface of V_S-ZIS could promote the adsorption and activation of O₂ on the catalyst surface, capturing photoinduced electrons to generate more O₂^-·, thereby enhancing the selective oxidation ability of the catalyst towards HMF.

Key words: sulfur vacancy, ZnIn₂S₄, HMF, photocatalytic, selective oxidation, DFF