Pd-decorated CuO/g-C₃N₄ heterostructure for visible-light-driven levofloxacin degradation

In this study, a Pd-decorated CuO/g-C₃N₄ heterostructure was synthesized via a facile hydrothermal-calcination route and evaluated for the visible-light-driven degradation of levofloxacin (LEV). The obtained CuO/g-C₃N₄-Pd photocatalyst exhibited enhanced photocatalytic performance, achieving 91.3% degradation of LEV (2.0 mg L^-1) within 90 min using 50 mg of photocatalyst under visible-light irradiation (λ > 420 nm) with a 300 W Xenon lamp, with an apparent pseudo-first-order rate constant of 0.02751 min^-1, which was higher than those of CuO/g-C₃N₄ (0.01378 min^-1), g-C₃N₄-Pd (0.00950 min^-1) and CuO (0.00689 min^-1) and retaining 81.1% degradation efficiency after four consecutive cycles. Structural and surface analyses confirmed the successful integration of CuO, g-C₃N₄, and Pd species within the composite. UV-vis diffuse reflectance spectroscopy and finite-difference time-domain (FDTD) simulations suggested improved visible-light harvesting and localized electromagnetic-field enhancement after Pd incorporation. Density functional theory (DFT) calculations revealed the formation of Cu-N, Pd-N, and Pd-C interfacial bonds, indicating electronic coupling among CuO, g-C₃N₄, and Pd. In addition, DFT results demonstrated strong adsorption of CO on Pd sites, suggesting that Pd may provide favorable adsorption and activation sites for carbon-containing species generated during photocatalytic degradation. Based on the combined experimental and theoretical results, a possible direct Z-scheme charge-transfer pathway was suggested for the CuO/g-C₃N₄-Pd heterostructure. The enhanced photocatalytic performance is attributed to the synergistic effects of improved visible-light harvesting, interfacial electronic interactions, and Pd incorporation. These findings provide useful insights into the design of efficient visible-light-responsive photocatalysts for antibiotic-contaminated wastewater treatment.