Synergistic activation of persulfate by oxychar and LDH for efficient degradation of PLA microplastics

This is the authors' abstract. We don't add key points for this paper.

Polylactic acid microplastics (PLA-MPs) pose a persistent risk in the aquatic environment due to incomplete degradation under natural conditions. Here, a FeMg-LDH-modified oxychar composite (OC-LDH) was prepared via low-temperature partial oxidation and evaluated as a persulfate (PS) activator for the degradation of PLA-MPs. During oxychar synthesis, FeMg-LDH promoted the activation of O 2 and left more oxygen-containing functional groups (OCFGs) on the surface of OC-LDH. In batch degradation experiments, OC-LDH achieved the highest weight loss (50.2%) of PLA-MPs in 30 days, outperforming oxychar and FeMg-LDH alone and indicating a synergistic effect between the two components. Moreover, OC-LDH maintained about 84% of its initial activity after three reuse cycles, with Fe leaching below 0.3 mg/L. Mechanistically, the active species attack the PLA backbone (ester) before oxidizing terminal C-H groups. Quenching experiments and EPR confirm that the PS activation proceeded through both radical pathways (SO 4 •- •OH, O 2 •- ) and non-radical ones ( 1 O 2 , electron transfer). XPS points to Fe(II) and OCFGs (especially C=O) on the OC-LDH as the key reaction sites. Meanwhile, the oxychar matrix also helped to disperse LDH, promoted Fe(II)/Fe(III) redox cycling and improved electron transport, all of which boosted PS activation. Overall, this work offers a recyclable catalyst design and practical insight into the synergistic roles of oxychar and LDH in PS activation for PLA-MPs remediation in water.