Citric acid-assisted in situ preparation of MoIn2S4/CQDs with few-layer promotes charge transfer and enhances photocatalytic activity

Ternary metal chalcogenides as promising photocatalysts and introducing carbon quantum dots (CQDs) as a dopant to enhance their photocatalytic activity. In this study, MoIn 2 S 4 and MoIn 2 S 4 /CQDs composite photocatalysts were successfully synthesized utilizing an in-situ hydrothermal method, in which citric acid served as both the carbon source and surfactant. Among the prepared catalysts, the MoIn 2 S 4 /CQDs composite photocatalyst with the optimal ratio (MoIS/CQDs-1.0 g) exhibited the highest photocatalytic performance, achieving a removal rate of 94.4 % for methylene blue (MB) after 60 min of simulated solar illumination. The superior performance was primarily attributed to the upconversion photoluminescence effect of CQDs , which enhanced the light absorption of MoIn 2 S 4 . Also, the few-layer configuration of MoIn 2 S 4 as a matrix possessed numerous active sites to significantly minimize the aggregation of CQDs . Furthermore, the CQDs acted as electron acceptors and transport centers, inhibiting the rapid recombination of photogenerated carriers and accelerating electron transfer. Additionally, through trapping experiments and electron paramagnetic resonance (EPR) tests, the primary active species responsible for photocatalytic degradation was identified as superoxide radicals (·O 2 – ). Based on these findings, a possible photocatalytic mechanism for MoIS/CQDs-1.0 g was proposed. This study provided a novel, stable and efficient MoIn 2 S 4 modified with CQDs photocatalyst for water treatment.