Regenerable Ag-Modified Cu2O/g-C3N4 Heterojunction for Photocatalytic Dye Removal and Surface-Enhanced Raman Sensing

Persistent dye pollutants call for analytical platforms that can both sensitively identify trace contaminants and enable efficient, reusable removal under mild conditions. In this study, we constructed a plasmon-assisted Cu2O/g-C3N4/Ag ternary heterojunction to integrate visible-light photocatalytic degradation and SERS sensing for dye pollutants. Structural and spectroscopic characterizations confirmed the successful integration of Cu2O, g-C3N4, and metallic Ag, while optical and photoelectrochemical measurements revealed enhanced visible-light response and improved charge separation in the optimized composite. By tuning Ag loading, the optimized CGA-5 sample achieved 97.6% removal of methyl orange within 60 min and followed pseudo-first-order kinetics with a rate constant of 0.04093 min–1, while maintaining stable activity over repeated photocatalytic cycles. Photoelectrochemical responses and spectroscopic analyses, together with radical-trapping experiments, collectively support an Ag-mediated Z-scheme charge-transfer pathway that suppresses carrier recombination and preserves strong redox capability, with photogenerated holes as the dominant oxidative species and reactive oxygen species contributing in an auxiliary role. Beyond photocatalysis, CGA-5 enables sensitive and reproducible SERS detection using 4-ATP and methyl orange (MO) as probes, achieving an enhancement factor (EF) 1.51 × 105 for 4-ATP, a detection limit down to 10–5 M for MO, and spot-to-spot reproducibility with an RSD below 11.06%. Importantly, four consecutive detection, photocleaning, and redetection cycles demonstrated that the regenerated substrate retained a clearly detectable SERS response, confirming its practical reusability. This work demonstrates a Z-scheme plasmonic coupling strategy that unifies efficient degradation, reusable catalysis, and regenerable SERS detection in a single material platform, offering a practical route toward integrated pollutant monitoring and remediation.