Phenoxyl mediators improve enzymatic degradation of organic pollutants: Effect and mechanism

Abstract

A mediation strategy can effectively overcome the low reaction activity of enzymes with nonspecific substrates. In this study, we demonstrated how phenol compounds can mitigate the substrate limitation of HRP in catalytic degradation of various organic pollutants. In a classical HRP/H2O2 system, phenol and natural phenolic compounds (4-HBA & pHBA), exhibited up to over 100-fold enhancement in eliminating organic dyes and persistent antibiotics while the loading is only 2–5 wt%. A combination of molecular modelling, docking and frontier orbital energy analysis was employed to elucidate the catalytic performance and mechanism. We revealed that (1) generating phenoxyl radicals required the proximity of mediators to the HRP active centre, and (2) the subsequent efficient radical transfer to pollutants was determined by the large energy gap between the SOMO energy of phenoxyl radicals and the HOMO energy of phenols. When considering phenols as pollutants, we showed a synergistic effect on catalytic degradation of phenols, dyes, and tetracycline with a removal efficiency of 71–92 %. Overall, this work not only demonstrates that phenoxyl mediators can overcome the lower efficiency and substrate-specificity limitations of the HRP/H2O2 system but also revealed their structure-mediation relationship, implying great potential in the biodegradation of diverse pollutants and their mixtures.