Green synthesis of 2 % g-C3N4/SnS2-V3/CQD1 composite photocatalyst from waste plant soot for efficient U(VI) removal: Mechanistic insights

Heavy metal U (VI) wastewater is a difficult problem in water treatment because U (VI) readily dissolves in water and exhibits significant radiotoxicity and chemical toxicity. In the current work, the photocatalytic elimination of U (VI) is realized through the application of the Z-scheme 2 % g-C3N4/SnS2-V3/CQD1 photocatalytic system. The system demonstrates high removal efficiency, efficient collection ability of natural visible light and considerable upconversion performance. Employing uranyl nitrate hexahydrate (N2O8U·6H2O) as the simulated pollutant of heavy metal U (VI), the 2 % g-C3N4/SnS2-V3/CQD1 achieved a removal rate of 98.84 % in 30 min under the condition of pH = 3, and the reaction rate constant (k) was 0.09972 min−1. Cycling stability tests demonstrated consistent performance of the photocatalyst over four repeated cycles, indicating its potential practical application in heavy metal pollution remediation. The investigation into the boosted photocatalytic activity delved into the analysis of optical properties, including the ultraviolet–visible diffuse reflection spectrum (UV–vis DRS), photoluminescence spectroscopy (PL), and ultraviolet photoelectron spectroscopy (UPS). Additionally, electrochemical tests, such as Mott-Schottky (M−S) plots, electrochemical impedance spectroscopy (EIS), and photocurrent response, were employed to unravel the underlying factors contributing to this enhancement. Furthermore, we proposed a credible catalytic mechanism for the photocatalytic system. The Z-scheme photocatalytic model serves to enhance the conveyance of photogenerated carriers, thereby mitigating the electron-hole recombination rate within the photocatalyst. This work not only provides ideas and strategies for the construction of other multi-functional composite photocatalysts, but also pioneers a novel approach for addressing heavy metal pollution.