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Electron beam synergetic removal of microplastics and hexavalent chromium: Synergetic removal process and mechanism
Summary
Electron beam irradiation was tested as a method to simultaneously degrade PVC microplastics and reduce toxic hexavalent chromium (Cr(VI)) in contaminated water, finding a synergistic effect where treating both together improved chromium removal from 57% to 92% compared to treating either contaminant alone. The mechanism involves electron beam aging of PVC generating reactive compounds that chemically reduce chromium, while the chromium in turn accelerates PVC breakdown. This dual-pollutant removal approach offers a novel strategy for treating industrial wastewater containing both plastic debris and heavy metal contamination.
Microplastics are ubiquitous in the environment and aged microplastics are highly susceptible to absorbing pollutants from the environment. In this study, electron beam was innovatively used to treat PVC composite Cr(VI) pollutants (Composite contaminant formed by polyvinyl chloride microplastics with the heavy metal hexavalent chromium). Experiments showed that electron beam was able to achieve synergistic removal of PVC composite Cr(VI) pollutants compared to degrading the pollutants alone. During the electron beam removal of PVC composite Cr(VI) pollutants, the reduction efficiency of Cr(VI) increased from 57% to 92%, Cl concentration increased from 3.52 to 12.41 mg L, and TOC concentration increased from 16.72 to 26.60 mg L. The research confirmed that electron beam can effectively promote the aging degradation of PVC, alter the physicochemical properties of microplastics, and generate oxygen-containing functional groups on the surface of microplastics. Aged microplastics enhanced the adsorption capacity for Cr(VI) through electrostatic and chelation interactions, and the adsorption process followed second-order kinetics and the Freundlich model. Theoretical calculations and experiments demonstrated that PVC consumed oxidizing free radical through dechlorination and decarboxylation processes, generating inorganic ions and small organic molecules. These inorganic ions and small organic molecules further reacted with oxidizing free radical to produce reducing free radicals, facilitating the reduction of Cr(VI). Cr(VI) continuously consumed the educing free radicals to transform into Cr (Ⅲ), enhancing the system oxidative atmosphere and promoting the oxidation degradation of PVC. This study investigated the formation and synergistic removal processes of PVC composite pollutants, offering new insights for controlling microplastics composite pollution.