Design of tertiary Z-scheme CuO–ZnO@MXene photocatalyst with superior visible-light activity for decomposition of nanoplastics

Plastic pollution has resulted in the widespread accumulation of nanoplastics (NPs) in aquatic environments, highlighting the need for innovative remediation strategies. In this study, a tertiary z-scheme CuO–ZnO/MXene nanocomposite was developed for the visible-light-assisted degradation of polyethylene-based NPs. ZnO particles were doped with 8 % CuO to form a p-n type heterojunction, and the resulting CuO–ZnO nanoparticles were anchored onto two-dimensional MXene sheets through a sono-precipitation dispersion method, forming a ternary z-scheme photocatalyst with enhanced surface area. The composite exhibited a low electron-hole recombination rate and a tunable band gap (~2.55 eV), enabling efficient visible-light absorption. Under visible light irradiation, the optimized CuO–ZnO/50 % MXene photocatalyst achieved over 90 % degradation of polystyrene-based NPs (10 mg.L −1 ) at neutral pH, substantially outperforming CuO–ZnO without MXene. Photoluminescence and electrochemical analyses confirmed effective charge separation, facilitated by the CuO–ZnO heterojunction and MXene's conductive network. Mechanistic studies revealed that photogenerated holes and electrons oxidized the polymer chains, breaking them into smaller oxygenated intermediates, ultimately leading to mineralization. Notably, amino-functionalized polystyrene degraded most rapidly, highlighting the influence of surface chemistry. The photocatalyst retained its activity over four reuse cycles with minimal loss. This work demonstrates the potential of MXene-integrated CuO–ZnO photocatalysts for sustainable nanoplastic remediation under visible light. • MXene loading enhanced the physicochemical properties of the photocatalyst. • FTIR and TOC confirmed the oxidation of nanoplastics during degradation. • CuO-ZnO/50 % MXene photocatalyst achieved 91.7 % degradation of amino-polystyrene. • pH and nanoplastic type were the key parameters in photodegradation efficiency.