DFT-Based Molecular-Level Insights into PFAS Adsorption on a Biochar-Supported Single-Atom Zinc Catalyst (SAZnC@Bc)

Single-atom metal catalysts (SAMCs) supported on substrates, such as biochar, have emerged as promising materials for per- and polyfluoroalkyl substance (PFAS) remediation. Their effectiveness lies in promoting degradation via oxidation or reduction. However, the adsorption behavior of PFAS onto SAMC active sites, a critical prerequisite to degradation, remains poorly understood. In this study, we employed density functional theory (DFT) to investigate PFAS adsorption behavior on single-atom zinc catalysts supported on biochar (SAZnC@Bc) with Zn–N4 coordination. Three representative compounds─perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and perfluorooctanesulfonic acid (PFOS)─were selected for analysis. We explored the influence of local coordination structures containing pyridinic, pyrrolic, or mixed nitrogen atoms. Our results show that the nitrogen composition and zinc coordination significantly affect the surface charge of SAZnC@Bc and, consequently, the PFAS adsorption strength. The configuration with four pyridinic nitrogen atoms exhibited the most positive surface charge and the highest PFAS– adsorption. All PFAS– molecules adopted a parallel orientation relative to the surface, with their functional groups facing the Zn–N4 site. The computed adsorption energy trend is PFBA– < PFOS– < PFOA–. These findings provide critical molecular-level insights to guide the rational design of SAMC-based materials for effective PFAS remediation.