Impact of microplastics on 4-chlorophenol degradation via MnOOH-catalyzed periodate activation

Phenolic compounds such as 4-chlorophenol (4-CP) are widely discharged from various industries that pose significant threats to human health and environment due to their toxicity and resistance to conventional treatment methods. In this study, hydrothermally synthesized MnOOH was used to activate periodate (PI), forming PI/MnOOH for degradation of 4-CP. The effect of microplastic (MP) coexistence on the performance of PI/MnOOH was evaluated. The degradation of 4-CP by PI/MnOOH was 92.53 ± 0.93 %, much higher than PI oxidation itself (23.85 ± 1.19 %) and that of MnOOH alone (11.82 ± 0.59 %), confirming the effective activation of IO₄^- ions by the synthesized MnOOH to generate free radicals. The PI/MnOOH process achieved degradation efficiency of 98.75 % at solution pH of 3 with a kinetic rate constant (k_obs) of 0.062 ± 0.003 min^-1. The quenching experiments suggested that reactive species, including IO₃^• (93.94 %), ¹O₂ (88.03 %), O₂^•- (61.97 %), and ^•OH (27.42 %) were detected. The degradation efficiency of 4-CP without MP was 97.54 ± 0.98 %, which decreased to 94.57 ± 4.73 %, 88.67 ± 4.43 %, and 68.95 ± 0.69 % in the presence of polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC), respectively due to electrostatic interactions between the positively charged MnOOH and the negatively charged MPs as well as pore-blocking effects. This work provides new insights into MP interference in PI/MnOOH based advanced oxidation processes and highlights their environmental implications.