Water-mediated kinetic modulation of Z-scheme In₂O₃/Cu/Cu₂O heterojunctions for durable photocatalytic remediation

The practical deployment of cuprous oxide (Cu₂O) in photocatalytic remediation is severely restricted by its intrinsic photocorrosion and fast charge recombination. To address these issues, a novel water-mediated in situ one-pot hydrothermal-calcination strategy is developed to fabricate a robust ternary In₂O₃/Cu/Cu₂O heterojunction. Water acts as a kinetic regulator to precisely control Cu reduction and phase evolution, enabling intimate interfacial contact among In₂O₃, metallic Cu, and Cu₂O. The optimized composite shows outstanding photocatalytic activity for sulfamethoxazole (SMX) degradation under simulated sunlight, with a rate constant of 0.0181 min⁻¹, 36.2 times higher than pure Cu₂O. It also exhibits excellent photostability, retaining 94.4% activity after five cycles with negligible Cu leaching. Mechanistic studies reveal a Cu-mediated all-solid-state Z-scheme charge transfer pathway. The Cu bridge serves as an electron relay, extracting photogenerated electrons from the Cu₂O conduction band to recombine with holes in the In₂O₃ valence band. This suppresses Cu₂O self-reduction while maintaining high redox potential for reactive radicals (∙O₂⁻, h⁺) generation. This work provides a green, facile route to design stable multi-component Z-scheme photocatalysts for efficient removal of refractory pharmaceutical pollutants.