Efficient Visible-Light Degradation of Polyethylene Microplastics over a Co-Doped CeO2/g-C3N4 Composite

Abstract The widespread accumulation of microplastics in aquatic and terrestrial ecosystems has emerged as a critical global environmental challenge, posing serious risks to ecological and human health. The persistence of polyethylene (PE) microplastics in aquatic environments poses a significant environmental challenge due to their chemical stability and resistance to natural degradation. Herein, we report a visible-light-active Co−CeO2/g-C3N4 composite for the efficient photocatalytic degradation of PE microplastics. Structural and spectroscopic characterization confirmed successful formation of the Co−CeO2/g-C3N4 composite, with preserved crystalline phases, strong interfacial interactions, uniform dispersion of Co−CeO2 nanoparticles over g-C3N4, homogeneous elemental distribution, and enhanced visible-light absorption and interfacial charge-transfer behaviour. Under visible-light irradiation, the composite achieved 59.76 ± 0.8% PE mass loss within 24 h, substantially outperforming the individual components. Oxidative degradation was further supported by an increase in the carbonyl index from 0.05 to 1.38, together with pronounced surface erosion, fragmentation, and increased roughness. EPR and radical-scavenging experiments identified •OH and O2•− as the major reactive species, with •OH playing the predominant role. LC−MS and TOC analyses confirmed the formation and subsequent transformation of soluble PE-derived intermediates. MTT-based cytotoxicity assessment using HepG2 and MCF-7 cells further showed that the degradation-product-containing aqueous phase did not exhibit greater cytotoxicity than pristine PE under the tested conditions. These findings demonstrate the potential of Co−CeO2/g-C3N4 for visible-light-driven PE microplastic degradation and highlight the potential of advanced heterostructured photocatalysts for environmental remediation.