Facile synthesis of carbon-doped ZnO with oxygen-vacancy and its photocatalytic degradation performance for PS microplastics.

To address the poor photocatalytic activity of ZnO caused by rapid charge carrier recombination, we synthesized carbon-doped porous ZnO with oxygen-vacancy via a one-step pyrolysis of zinc oxalate precursor. EPR confirmed the presence of oxygen vacancies (g = 2.0031), while SEM and BET revealed a loose porous network (specific surface area 37.8 m2/g) formed by in-situ COx release. Photochemical tests showed that the synergy between carbon doping and oxygen vacancies effectively suppresses electron-hole recombination and narrows the bandgap to 3.17 eV. In the photocatalytic degradation of 3-μm PS microplastics, 400-2.5 achieved a mass loss of 63.9% within 6 h, with a normalized degradation capacity of 0.213 mg·mg-1·h-1-approximately 1.5 times that of commercial ZnO. Radical trapping experiments identified superoxide radicals as the dominant active species (activity decreased from 63.7% to 44.3% upon PBQ addition), with holes and •OH playing auxiliary roles. HRGC-MS and UPLC-MS analysis of the filtrate unambiguously detected nine key intermediates, including benzene, benzoic acid, acetophenone, styrene, p-xylene, ethylbenzene, and 2,2'-biphenyldicarboxylic acid. Based on these findings, three parallel degradation pathways-main-chain scission, side-chain oxidation, and benzene ring hydroxylation/ring-opening-are proposed, demonstrating that the PS backbone is progressively attacked by reactive species and ultimately mineralized to CO2 and H2O.