Molecular Engineering toward Pyrrolic N-Rich M-N4 (M = Cr, Mn, Fe, Co, Cu) Single-Atom Sites for Enhanced Heterogeneous Fenton-Like Reaction

Heterogeneous Fenton-like reactions (HFLR) are promising alternative strategies to address the inherent limitations of the classic Fenton systems. Herein, a facile and scale-up approach for the synthesis of transition metal single-atom sites (SA-TM, TM = Cr, Mn, Fe, Co, Cu) coordinated onto pyrrolic N-rich g-C3N4 (PN-g-C3N4) scaffold is developed. The regulated pyrrolic N-rich SA-TM catalytic sites exhibit excellent performances for HFLR. As a model of SA-TM/PN-g-C3N4, SA-Cr/PN-g-C3N4 is efficient for the catalytic oxidation of bisphenol A via HFLR under visible light with outstanding cyclic stability and wide effective pH range (3.0-11.0). The synergy of photocatalysis and single-atom catalysis leads to accelerated production and separation of charge carriers as well as the cycling of Cr3+/Cr2+ couple, consequently boosting the performance in HFLR. Theoretical calculations indicate that the Cr(II)-N-4 sites with the metalloporphyrin-like structure are more reactive than the doped Cr(II) sites in the g-C3N4 matrix, which act as the peroxidase-mimicking nanozyme for efficient and homolytic cleavage of peroxide O-O in H2O2. This study expands the family of the iron-free Fenton-like systems and provides new strategies to the rational design and precise regulation of on-demand multifunctional single-atom catalysts for advanced water remediation.