Direct and efficient reduction of perfluorooctanoic acid using bimetallic catalyst supported on carbon

A variety of metal elements have exhibited strong reductive and dehalogenative capabilities for the removal of persistent organic pollutants, owing to electron transfer or electron-hole activation through various methods. Herein, a bimetallic C_Ni-Al₂O₃ structure (AlC_Ni) was successfully synthesized to simultaneously function as sorbent and catalyst in the reduction of perfluoroalkyl carboxylic acids (PFOA) polluted wastewater. Using a reaction period of 3 h, 98% of PFOA was removed by AlC_Ni through a mechanochemical stirring method and 70.43% of fluorine ions was released from PFOA anchored onto the surface of AlC_Ni. Both thermocatalysis and photocatalysis technologies were incorporated and compared when utilized in tandem with AlC_Ni to mitigate the PFOA. In addition, peroxymonosulfate (PMS) and sodium sulfite (Na₂SO₃) were also integrated into experiments, separately, as a strong oxidant and reductant to improve the degradation effect of PFOA. However, the degradation efficiency of both were lower than that of AlC_Ni, even when assisted by elevated temperatures and ultraviolet irradiation. The feasibility of employing AlC_Ni for PFOA degradation was further investigated at various temperature and pH conditions. The data obtained from HPLC-MS/MS, TOC, and IC with multiple characterizations of AlC_Ni/PFOA, proposed the predominant degradation pathways comprising adsorption, defluorination-hydroxylation, and decarboxylation. This study provides a valuable remediation method without utilizing chemical agents and special activation for PFOA by AlC_Ni, which can be suitable for large-scale sewage treatment applications.