Hydroxyl radical dominated elimination of plasticizers by peroxymonosulfate on metal-free boron: Kinetics and mechanisms

Plasticizer pollution in drinking water and aquatic systems has raised global concerns due to the lasting and chronic hazards to marine life and public health. Metal-free materials are promising as green catalysts for wastewater purification. In this study, amorphous boron was applied as a metal-free activator to decompose peroxymonosulfate (PMS) for the degradation of plasticizers in water. Integrating radical trapping and selectively quenching tests with kinetic evaluation and electrochemical analysis, hydroxyl radical was found to be the dominating reactive oxygen species (ROS). With a strong oxidative capacity, the boron/PMS system can effectively degrade both bisphenols and phthalates plasticizers. In contrast, a carbon nanotube-catalyzed PMS system mediated a nonradical pathway to oxidize the electron-rich plasticizer (bisphenol A), but ineffectively to decompose the highly recalcitrant phthalates plasticizers (diethyl phthalate). Moreover, we unveiled that the boron surface was oxidized to boron oxide during the redox reaction, and the oxide would be self-cleaned in the acidic solution to regenerate fresh boron and restore the activity during the cyclic operations. Therefore, this work not only gains new insights into the radical and nonradical oxidations by metal-free catalysis, but also provides feasible technologies for plasticizer purification in water.