Mechanistic exploration of interfacial electron transfer in CQDs@MXene heterostructure for visible light photocatalytic reduction.

This study aims to elucidate the interfacial electron distribution and transfer mechanism in a 0D-2D heterostructure composed of carbon quantum dots (CQDs) and Ti3C2Tx MXene, with the goal of efficient visible-light-assisted reduction of representative aqueous contaminants, including methylene blue, methyl orange, p-nitrophenol, and hexavalent chromium. CQDs were introduced onto the MXene surface through chemical interactions, constructing the CQDs@MXene heterostructure and inducing pronounced interfacial charge redistribution. Density functional theory (DFT) calculations revealed that the surface functional groups of CQDs attracted electrons from MXene, leading to the formation of electron-accumulated regions at the interface. This electron-rich configuration indicates that the CQDs and the interfacial domains can function as electron reservoirs. Meanwhile, carbon centers facilitated electron release, providing a favorable electron-transfer pathway for reduction reactions. In photocatalytic reduction tests, CQDs@MXene efficiently collected and delivered both photoexcited electrons generated under visible light and externally supplied electrons originating from NaBH4, achieving rapid reduction of diverse target pollutants within 5 min. By correlating experimental observations with theoretical analysis, the overall processes of electron accumulation, migration, and delivery across CQDs@MXene heterointerface were comprehensively clarified. Finally, this study provides mechanistic insights for the interfacial engineering of CQDs@MXene-based systems for efficient contaminant reduction in water.