Dual-functional Cu₂O/g-C₃N₄ heterojunctions: a high-performance SERS sensor and photocatalytic self-cleaning system...

This study introduces a multifunctional device based on Cu₂O/g-C₃N₄ monitoring and purification p-n heterojunctions (MPHs), seamlessly integrating surface-enhanced Raman scattering (SERS) detection with photocatalytic degradation capabilities. The SERS and photocatalytic performances of the Cu₂O in various morphologies, g-C₃N₄ nanosheets (NSs) and Cu₂O/g-C₃N₄ MPHs with different g-C₃N₄ mass ratios were systematically evaluated, with a particular emphasis on the Cu₂O/g-C₃N₄-0.2 MPH, where g-C₃N₄ constituted 20% of the total mass. Multiple optical and electrochemical tests revealed that the Cu₂O/g-C₃N₄-0.2 MPH effectively enhances charge separation and reduces charge transfer resistance. The Cu₂O/g-C₃N₄-0.2 SERS sensor exhibited a relative standard deviation (RSD) below 15% and achieved an enhancement factor (EF) of 2.43 × 10⁶ for 4-ATP detection, demonstrating its high sensitivity and consistency. Additionally, it demonstrated a 98.3% degradation efficiency for methyl orange (MO) under visible light within 90 min. Remarkably, even after 216 days, its photocatalytic efficiency remained at 93.7%, and it retained an 84.0% efficiency after four cycles. XRD and SEM analyses before and after cycling, as well as after 216 days, confirmed the structural and morphological stability of the composite, demonstrating its cyclic and long-term stability. The excellent performance of the Cu₂O/g-C₃N₄ MPH is attributed to its Z-type mechanism, as verified by radical trapping experiments. The evaluation of the self-cleaning performance of the Cu₂O/g-C₃N₄-0.2 SERS sensor demonstrated that its Z-scheme structure not only provides excellent self-cleaning capability but also enables the detection of both individual and mixed pollutants, while significantly enhancing the SERS signal response through an effective charge transfer enhancement mechanism.