Local Electron Density Regulation of Iron Single Atoms by Adjacent Nitrogen Vacancies for Ultra-stable Photo-Fenton-Like Reactions

Abstract

Single-atom catalysts (SACs) have emerged as efficient oxidant activation materials, yielding highly reactive species in organic wastewater decontamination. However, the fundamental studies on single metal sites are susceptible to insufficient electron input and instability. Herein, we first used theoretical calculations to predict the optimal locations of nitrogen vacancy and Fe single-atom sites and also revealed that dual sites could significantly enhance light absorption, charge separation, and transfer. Guided by the computational predictions, introducing adjacent nitrogen vacancies to regulate the electron density of single iron atoms were finely designed and then served as a photo-activator for low-toxic peracetic acid, exhibiting a superior and ultra-stable (15 cycles) activity for eliminating various organic pollutants. The catalytic performance exceeded ~27.4 times that of the original g-C3N4 equivalent over a pH range of 3-9. Electrons trapped in nitrogen vacancies could be rapidly transferred to nearby Fe sites assisted by a visible light switch, accelerating their ability to reduce the "peracetic acid-catalyst" intermediate. Theoretical calculations were further performed to uncover the synergy of dual engines, and the enhanced adsorption and activation of reactive molecules were detected. The electron reduction pathways on the conduction band were sufficiently exposed to produce highly active species, favoring photocatalytic reactions. This work provides insights into the rational design of ultra-efficient and -stable SACs for organic wastewater decontamination in a photo-Fenton-like system.