Concentration-decomposition technology for perfluorooctanoic acid mineralisation based on adsorption by ZIF-8 and subsequent electrolytic oxidation.

Abstract

Electrolytic oxidation is a promising decomposition method for perfluorooctanoic acid (PFOA) because it is relatively mild compared with incineration and ultraviolet (UV) treatment, does not use chemicals, and has a low environmental impact. However, the electrolytic oxidation method is inefficient when the concentration of the target substance is low. In this study, a new concentration-decomposition technology based on adsorption by the metal-organic framework zeolitic imidazolate framework (ZIF)-8, followed by electrolysis, was developed for PFOA degradation. The concentration of PFOA was increased by performing adsorption with reduced-pressure filtration, resulting in an adsorption efficiency of >90%. Then, considering that the structure of ZIF-8 can be destroyed under strong acid conditions, a H₂SO₄ aqueous solution was added after adsorption to destroy ZIF-8, followed by neutralisation by adding a NaOH aqueous solution. Subsequent electrolysis of PFOA reached the same level of mineralisation energy efficiency as that obtained via conventional electrolysis. The mineralisation energy efficiency under the five-fold concentrated condition with acid-base treatment was 1.2 mg/Wh, which is higher than that of other degradation methods. Although optimisation of the amounts of ZIF-8 and the acid-base reagents is still required, this study provides a new foundation for developing efficient approaches for PFOA detoxification, including PFOA desorption via acid-base treatment and energy efficiency enhancement through the concentration process.