Highly efficient defluorination of perfluorooctanoic acid by a BiOCl-ND photocatalyst: Enhanced charge transfer and synergistic mechanism

Considerable attention has been given to the control of perfluorooctanoic acid (PFOA) environmental pollution due to its degradation resistance and potential risks. In this study, Bismuth oxychloride based nanodiamond (BiOCl-ND) composite materials were successfully synthesized by using hydrothermal method. The complete decomposition of PFOA and a high defluorination ratio of 74.6% by BiOCl-ND 10:1 was obtained under UV light irradiation within 60 min, and the composite's degradation rate constant was nearly 3.8 times than that of pure BiOCl. It was demonstrated that critical roles played in PFOA degradation were photogenerated holes (h⁺) and superoxide radicals (·O₂⁻). A synergistic effect between BiOCl and ND and the heterostructure was revealed, the differences of the energy band structure between BiOCl and ND reduced the recombination of photogenerated e⁻-h⁺ and enhanced the charge transfer. In this process, a large number of h⁺ with oxidizing properties and·O₂⁻ generated from both BiOCl and ND played a critical role, and oxygen vacancies (OVs) also participated in the reaction as active species and contributed to electron transfer. Additionally, the photocatalytic decomposition intermediates of PFOA and the release of fluorine ions were analyzed to verify the effective defluorination of PFOA, and the results confirmed a gradual decrease in the toxicity of the reaction matrix during PFOA degradation. Hence, these results might provide insights for the development of photocatalysts to improve the photodegradation effect of PFOA in water.