Complete defluorination of PFASs via photocatalytic reduction in water

Overview

Per- and polyfluoroalkyl substances (PFASs) represent persistent environmental contaminants whose C-F bonds resist conventional degradation pathways. This study demonstrates a photocatalytic approach to achieve near-complete defluorination of PFAS compounds through visible-light-driven reduction using 5,10,15,20-tetraphenyl (4-aminophenyl) porphyrin (TAPP) aggregate photocatalysts. The methodology operates without external chemical additives, addressing a critical gap in remediation technologies for these legacy contaminants.

Methods and approach

TAPP aggregates were employed as photocatalytic substrates under visible-light irradiation. The central mechanistic feature involves generation and stabilization of the TAPP radical species (TAPP•), which persists for extended periods under ambient conditions. The radical anion generates reductive electrons with a reduction potential of -2.68 V relative to the normal hydrogen electrode, sufficient to access C-F antibonding orbitals. Radical stability derives from intramolecular charge delocalization facilitated by electronic coupling between amino group lone-pair electron distributions and the porphyrin highest occupied molecular orbital. This steady radical strategy was evaluated for defluorination efficacy across PFAS substrates.

Key Findings

TAPP aggregates achieved approximately 100% defluorination of PFAS compounds under visible-light conditions. The TAPP• radical demonstrates remarkable stability, with measured lifetimes exceeding seven days under ambient conditions. The sustained reduction potential of -2.68 V enables direct electron injection into C-F antibonding orbitals, initiating defluorination pathways. The synergistic electronic overlap between amino group orbitals and the porphyrin macrocycle provides the mechanistic basis for extended radical lifetimes and consequent photocatalytic performance.

Implications

This work establishes a charge-delocalization engineering strategy for designing photocatalysts capable of degrading exceptionally stable halogenated pollutants. The near-quantitative defluorination of PFAS without supplementary chemical additives presents a pathway toward practical remediation of contaminated aqueous systems. The approach is generalizable to other persistent organic contaminants characterized by strong C-X bonds resistant to conventional treatment methods. The extended radical stability under ambient conditions suggests potential scalability and reduced operational complexity compared to existing defluorination technologies. Further investigation into substrate scope, mineralization pathways, and performance in complex environmental matrices would strengthen technological viability for environmental applications.