A layered g-C3N4 support Single-Atom Fe-N4 catalyst derived from hemin to Activate PMS for Selective degradation of electron-rich compounds via singlet oxygen species

Single-atom catalysts (SACs) have been widely applied in electrocatalysis, photocatalysis and advanced oxidation processes. However, the synthesis of Fe SACs supported by layered g-C3N4 remains challenging due to the high temperatures required for Fe single-atom (Fe-SA) sites formation, which can lead to the decomposition and curling of g-C3N4. Herein, Fe SACs loaded on layered g-C3N4 (Fe-SA@CN) were synthesized via an one-step pyrolysis using the pre-coordination metal precursor (hemin). The pre-coordinated structure in hemin prevented Fe atoms aggregation, while the planar structure of hemin suppressed the curling of g-C3N4 at high temperature. The structures of the resulting material, including the atomically dispersed Fe-SA sites and its coordination environment (Fe-N4), were characterized by AC-STEM and XAFS. The doping of Fe-SA sites facilitates the fracture of C-N bonds in pyridinic N and boosts the recombination of C-C bonds, thereby lowering the initial temperature of thermal decomposition of g-C3N4 and improving the quality of the carbonization residue. Experimental tests and DFT calculations demonstrate that Fe-SA sites effectively decrease the adsorption energy of PMS, facilitating electron transfer processes. The Fe-SA@CN, with a Fe loading of 2.03 wt%, performs best in activating PMS for the degradation of aromatic compounds bearing electron-donating groups, which are mainly attacked by 1O2 generated on Fe-SA sites (above 90% 1O2 selectivity). This study highlights the role of precursor in the synthesis of single-atom catalysts, and provides insight for developing SACs for advanced oxidation processes.