Enhancement of the Coadsorption of Per- and Polyfluoroalkyl Substances onto Fe-MOF Derivative in Surface Water through Strengthening Hydrophobic Interactions

Severe harmful effects of per-fluoroalkyl and polyfluoroalkyl substances (PFAS) to ecology and human health have led many countries to continuously upgrade their control for PFAS, which poses higher requirements for the efficient removal of PFAS in water to ensure water resource security. In the present study, the three-dimensional/two-dimensional (3D/2D) structure of metal oxide immobilized on a carbon substrate of the Fe-based metal-organic frameworks (Fe-MOF) heat treatment derivative H:MIL-101(Fe) was constructed. H:MIL-101(Fe) could completely remove PFOA from pure water within 5 min, and complete recovery was achieved within 30 s. H:MIL-101(Fe) exhibited stable properties and can maintain its initial adsorption percentage after four cycles of PFAS adsorption. It was found that the high hydrophobic interface of H:MIL-101(Fe) was formed by partial carbonization during the Fe-MOF heat treatment, and a large number of unsaturated ═C-H bonds on the unstructured benzene ring were generated. Furthermore, cationic chelating agent, such as cetyltrimethylammonium bromide, were mixed with PFAS to synthesize more hydrophobic long-chain complexes; six PFAS containing 4-8 carbon atoms could be completely coadsorbed in surface water within 10 min at pH 7.0, mainly depending on the mechanism of hydrophobic interaction. This study develops a novel adsorption material that can match PFAS types to realize the effective coadsorption of PFAS in water, which provides new insights for removal of PFAS with different carbon chains based on improving hydrophobic interactions between adsorbents and adsorbates.