Removal of perfluorinated compounds at environmentally relevant concentrations on non-equivalent dual sites regulated by single-atom-strengthened biochar

Abstract

Removal of perfluorinated compounds (PFCs) at environmentally relevant concentrations in drinking water is challenging. A novel K single-atom-strengthened biochar (K1-BC) is designed to effectively adsorb the representatives of PFCs, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), from 1 μg/L to below 70 ng/L (CPFOA+PFOS) in tap water under dynamic mode, which meets a health advisory level in drinking water from the U.S. Environmental Protection Agency. Furtherly, an adsorption theory of non-equivalent dual sites (N-EDS) is firstly proposed to clarify the adsorption process and mechanisms, that is, the sites of K single-atom and adjacent C are the main adsorption sites for PFOA and PFOS. The difference charge density and adsorption energy reveal that the introduction of K single-atom could change the local environment to form the N-EDS, which could strengthen the adsorption ability of K1-BC to electronegative PFOA and PFOS. Moreover, the Bader charge transfer value of K1-BC is larger than that of Blank BC, implying that N-EDS construct a channel for electron transfer to enhance the adsorption ability and stability. This proposed adsorption theory is of vital significance to guide the synthesis of single-atom-strengthened biochar and the application for PFOA/PFOS removal at environmentally relevant concentrations in drinking water.