Hydrated electron produced on aluminum cathode mediates electro-reduction of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a globally concerning persistent organic pollutant (POP) due to its strong chemical stability, making it resistant to decomposition by conventional water treatment methods. Conventional advanced reduction processes (ARPs) involving hydrated electrons (eaq−) have been recognized as effective method of decomposing PFOA, which face the challenges of light shielding, chemical agent addition, and operation intricate. In this study, the unique properties of amphoteric metals aluminum (Al) were used as electrochemical cathode to generate eaq− for efficient PFOA removal. Experimental results indicated that 97.4 % PFOA was removed at the reaction time of 4 h (kobs = 0.0125 min−1, pH = 4), and the kobs of PFOA decomposition showed negligible pH dependence, ranging from 0.0125 min−1 to 0.0119 min−1 (pH 4 to pH 12). Quenching experiments and electron spin resonance (ESR) measurements confirmed that eaq− was the primary active species for PFOA removal. Chemiluminescence (CL) and electrochemiluminescence (ECL) measurements suggested that the eaq− was generated through direct contact between Al and the interfacial alkaline solution Al + 4OH− → Al(OH)4− + 3eaq−), which the local pH adjacent to Al cathode was in-situ adjusted to a basic environment to boost the production of eaq−. As an unprecedented eaq− production strategy, the Al cathode-based ARPs system demonstrates that PFOA degradation and defluorination performance are minimally affected by the initial pH, demonstrating its robustness and versatility in environmental remediation applications.