Z-scheme Cu2O/g-C3N4/Ag heterostructures: A novel approach for simultaneous water pollutant removal and real-time SERS monitoring

To address the challenge of achieving simultaneous pollutant removal and real-time monitoring in water remediation, Z-scheme Cu 2 O/g-C 3 N 4 /Ag heterostructures with integrated functionalities for synergistic adsorption, photocatalytic degradation, and surface-enhanced Raman scattering (SERS) detection were developed—hereafter referred to as APS-Hs (adsorption–photocatalysis–SERS heterostructures). Particular emphasis was placed on the Cu 2 O/g-C 3 N 4 /Ag-1.5 APS-Hs, incorporating an optimized 1.5 wt% Ag loading. Optical and electrochemical tests demonstrated that the Cu 2 O/g-C 3 N 4 /Ag-1.5 APS-Hs significantly enhanced charge separation efficiency and reduced charge transfer resistance. Under visible-light irradiation, the Cu 2 O/g-C 3 N 4 /Ag-1.5 APS-Hs attained a removal efficiency of 98.1 % for methyl orange (MO) within 45 min and sustained an efficiency of 84.0 % after three consecutive cycles. XRD and SEM analyses conducted before and after photocatalytic cycling confirmed the composite's outstanding structural and morphological stability. Notably, the Cu 2 O/g-C 3 N 4 /Ag-1.5 APS-Hs demonstrated the highest adsorption capacity (21.34 mg/g) among all samples. Zeta potential measurements revealed a surface charge reversal from + 22.35 mV to −10.29 mV, indicative of strong electrostatic interactions with anionic pollutants. Pseudo-second-order (PSO) kinetic modeling (R 2 =0.971) further established physisorption as the dominant mechanism. Radical trapping experiments verified that the enhanced photocatalytic performance originates from the Z-scheme charge transfer pathway. Additionally, the Cu 2 O/g-C 3 N 4 /Ag-1.5 APS-Hs substrate achieved a SERS enhancement factor of 3.1 × 10 6 and a broadband self-cleaning capability, underscoring its potential for integrated environmental remediation and sensing applications.