Concurrent redox reactions for perfluorocarboxylic acids decontamination via UV-activated tryptophan/carbon nanotubes

Abstract

The contamination and persistence of Perfluorooctanoic Acid (PFOA) in aquatic environments have escalated environmental concerns, driving extensive research into effective decontamination strategies. To enhance the removal efficiency of PFOA via Advanced Reduction Processes (ARP) utilizing UV irradiation of tryptophan (Trp), carbon nanotubes (CNT) were incorporated, resulting in the development of a UV-Trp/CNT system. This novel process demonstrated a significant improvement in PFOA removal kinetics, as well as defluorination and Total Organic Carbon (TOC) reduction, and was effective across a broad spectrum of perfluoroalkyl carboxylic acids (PFCAs). In addition to the advanced reduction mechanism driven by hydrated electrons ($e_{aq}^{-}$), quenching experiments, material characterization, and chemical calculations indicated that CNTs facilitated the enrichment of Trp and PFOA, enabling electron transfer from PFOA to Trp via the CNT surface. This established a novel reaction pathway for PFOA oxidation coupled with ARP. The sequential defluorination of -CF₂- groups was facilitated by $e_{aq}^{-}$, while the electron transfer mechanism enabled oxidative decarboxylation, electron rearrangement, CC bond cleavage, and carbon chain shortening. These oxidative and reductive processes alternated systematically, advancing the development of a synergistic redox approach for the removal of PFCAs and inspiring further exploration into the use of carbon materials to construct confined domains and catalyze the degradation of PFASs.