Thin interfacial film spontaneously produces hydrogen peroxide: mechanism and application for perfluorooctanoic acid degradation

Abstract

An effective decontamination method for soil remediation is a long-standing challenge. Herein, hydrogen peroxide (H₂O₂) was spontaneously produced in thin films generated by evaporating almost all of the water. H₂O₂-sensitive test strips and oxidation of 2-hydroxybenzophenone to 2-hydroxyphenyl benzoate confirmed the generation of H₂O₂. Experiments in which the reaction time and temperature were varied were performed and established the dependence of H₂O₂ production on the long-lasting thin films. H₂O₂ production was independent of irradiation and oxygen from the air or dissolved oxygen. Spin-trapping probe experiments suggested that electric fields in the thin interfacial films enabled the conversion of OH⁻ to hydroxyl radicals and then further recombination to H₂O₂. As a proof-of-principle experiment, perfluorooctanoic acid (PFOA) was effectively degraded on the thin films without catalysts, and UV irradiation could further facilitate the degradation. A degradation mechanism was proposed involving the formation of PFOA radicals on the thin interfacial films and the subsequent decomposition of the radicals with successive loss of CF₂. These findings have important implications for the development of decontamination methods for soil remediation based on thin films, because thin film formats are ubiquitous at the surface of soils and when aerosols fall onto a substrate.