Microplastic degradation and organic acids recovery via homogeneous catalytic wet air oxidation: Role of redox and Lewis acidity of metal ions.

The pervasive accumulation of microplastics (MPs) in aquatic and terrestrial ecosystems poses a growing threat to environmental and human health, yet current advanced oxidation technologies are constrained by inefficiency or reliance on excess oxidants. Here, a homogeneous catalytic wet air oxidation (CWAO) system using Cu2 + ions was developed to degrade polyethylene (PE) MPs and simultaneously recover value-added carboxylic acids. The system enables 98.7% weight loss of PE (1.0 g/L) and a liquid-phase total organic carbon of 489 mg/L at 170 °C, substantially outperforming non-catalytic WAO. About 57.1% of the PE carbon is transformed into carboxylic acid species, with a total dicarboxylic acid concentration reaching 186.9 mg/L. The catalyst functions through a synergistic dual-mechanism pathway, consisting of a Cu2+/Cu+ redox cycle that activates O2 to generate •OH radicals for C-C bond scission, and Lewis acidity that polarizes C-H and C-C bonds to lower the activation energy for oxidative cleavage, which enables controlled polymer chain scission and stepwise oxidation, including hydroxylation, carbonylation, and carboxylation. The system also exhibits applicability to other MPs or real-world PE-rich plastic waste, with more than 97.7% weight loss. This work establishes CWAO as a promising route that integrates environmental remediation with resource recovery for MPs treatment.