Multifunctional Ag-doped CuS surface nanostructures for simultaneous dye degradation and bacterial inactivation via visible-light activation

Abstract

This work reports a new dual-strategy approach for the preparation of nanostructured Ag-doped CuS (Cu_1−xAg_xS, x = 0.03) photocatalysts designed by the synergy of morphology control and band gap engineering for enhanced environmental cleanup. The hexagonal covellite phase, the successful lattice substitution of Ag ions, and the change from strongly agglomerated 65 nm particles to well-dispersed 55 nm nanoparticles were confirmed by systematic characterization using XRD, FTIR, SEM, and EDX analyses. In addition, I–V analysis demonstrated a remarkable increase in conductivity. Together with UV-vis DRS, PL, electrochemical impedance spectroscopy (EIS), and transient photocurrent response analyses, the results demonstrated that Ag doping decreased the bandwidth from 1.69 eV to 1.57 eV, strongly inhibited charge recombination, and improved interfacial charge transfer. Thus, 3% Ag-doped CuS with the best performance shows excellent photocatalytic activity, with almost 98.2% MB degraded in 80 min (k = 0.029 min⁻¹), which is 3.6 times higher than the activity of pristine CuS. In addition, an anti-bacterial assay revealed a 2.12-fold increase in the zone of inhibition against Escherichia coli (23.3 mm). Mechanistic information based on radical scavenging experiments and electron paramagnetic resonance (EPR) spectra indicated that ˙OH and ˙O₂⁻ were the major reactive species for dye mineralization and bacterial inactivation. Cyclic degradation experiments and after-cycling XRD analysis demonstrated that the material could be reused several times without any structural degradation.