Dual-functional Cu2O/g-C3N4 heterojunctions: a high-performance SERS sensor and photocatalytic self-cleaning system for water pollution detection and remediation

Abstract 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.