Fe-N/C single-atom catalysts with high density of Fe-Nx sites toward peroxymonosulfate activation for high-efficient oxidation of bisphenol A: Electron-transfer mechanism

A high-efficient iron-based heterogeneous catalyst is desired to active peroxymonosulfate (PMS). Due to a large catalytic contribution of atomically dispersed Fe-Nx sites, single-atom iron–nitrogen-carbon catalysts exhibit superior performance in the catalytic activation of PMS. Herein, a sequence of Fe-N-C SACs with atomically dispersed Fe-Nx sites, FeSA-N-C and FeSA-N/C, were prepared from Fe-doped ZIF-8 and FePc@ZIF-8, respectively. Single-atom Fe-Nx sites were confirmed to be the main active sites for PMS activation. FeSA-N/C-20 with a higher density of Fe-Nx sites exhibited superior catalytic performance to N/C, FeSA-N-C, FeSA-N/C-15, and FeSA-N/C-25 for BPA degradation. Integrated with chemical quenching experiments, electron spin resonance (ESR), in-situ Raman spectra, and electrochemical analysis, a nonradical pathway was demonstrated to dominate the degradation of BPA in the PMS + FeSA-N/C-20 system. More importantly, the nature of this nonradical pathway was found to be an electron-transfer regime instead of a high-valent iron or singlet oxygenation process. The BPA was adsorbed onto the Fe-Nx site by a “donor–acceptor complex” mechanism to form a nonradical PMS* intermediate during the process. Benefiting from this mechanism, the PMS + FeSA-N/C-20 system showed wide pH adaptation and high resistance to inorganic anions.