Photocatalysis oxidative desulfurization of dibenzothiophene in extremely deep liquid fuels on the Z-scheme catalyst ZnO–CuInS2–ZnS intelligently integrated with carbon quantum dots: performance, mechanism, and stability

Abstract

In this study, we improved the electrochemical and photocatalytic properties of the ZnO–CuInS₂–ZnS (ZCZ) material by integrating with carbon quantum dots (CQD) with particle sizes from 2 to 5 nm. The integration of ZnO–CuInS₂–ZnS with carbon quantum dots (ZnO–CuInS₂–ZnS/CQD:ZCZ–CQD) enhanced the visible light absorption, significantly reduced the electron–hole recombination rate, and facilitated the electron transfer and separation processes as confirmed by UV-visible diffuse reflectance spectroscopy (UV-vis DRS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). The successful integration of ZCZ with carbon quantum dots was confirmed using X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) methods. The ZCZ/CQD photocatalyst removed up to 98.32% of DBT after 120 minutes of reaction, maintained over 90% durability after 10 cycles, and retained its structure without any changes. The ZCZ photocatalyst integrated with CQD enhances faster dibenzothiophene (DBT) removal by 4.46, 3.24, 2.53, and 1.72 times compared to ZnO, CuInS₂, ZnS, and ZnO–CuInS₂–ZnS, respectively. Factors influencing the oxidation process of DBT including the mass of the photocatalyst, initial DBT concentration, stability, and reaction kinetics were studied. Through active species trapping experiments, this study demonstrated that the formation of ˙O₂⁻ and ˙OH radicals determines the reaction rate. The mechanism of photocatalysis on ZCZ–CQD materials and the intermediate products formed in the process of photocatalytic oxidative desulfurization of dibenzothiophene is proposed based on electrochemical measurements and GC-MS results.