Tailoring metal-pyridinic N4 sites in single-atom catalysts enables selectivity approaching 100% for 1O2 generation in water cleanup

Near-100% selective 1 O 2 generation via Fe-pyridinic N 4 sites. • Metal-atom utilization enhanced by 10 2 -10 4 -fold in FeSA-N-C-2S. • Fe-pyridinic N 4 shifts d -band center, lowering 1 O 2 energy barrier and tuning pathway. • 1 O 2 steady-state concentration positively correlates with Fe-pyridinic N 4 proportion. • A universal strategy creates various metal-based SACs with > 90% 1 O 2 selectivity. The type and quantity of nitrogen ligands in the first-shell coordination structure (FSCS) of single-atom catalysts (SACs) govern catalytic performance. However, current research largely focuses on nitrogen atom count, overlooking its chemical structure. Herein, by reconfiguring the FSCS from Fe-pyrrolic N 4 to Fe-pyridinic N 4 (FeSA-N-C-2S), we achieve selectivity approaching 100% for singlet oxygen ( 1 O 2 ) generation. Mechanistically, Fe-pyridinic N 4 shifts the d -band center toward the Fermi level via axial d_z² orbital hybridization, reducing Fe d -orbital occupancy, which enhances electron transfer through the conjugated π-system of pyridinic N, lowering the activation barrier for 1 O 2 generation and optimizing the reaction pathway. This facilitates complete degradation of electron-rich pollutants like 2,4,6-trichlorophenol, with a 4.3-fold increase in rate constant and a 21.5-fold higher metal-atom utilization efficiency compared to the FeSA-N-C-1S. Moreover, 1 O 2 steady-state concentration exhibits a significant linear positive correlation with Fe-pyridinic N 4 proportion, which can be precisely modulated by adjusting the pyrolysis temperature and metal-to-precursor ratio. This insight extends to other transition metals (Co, Cu, Mn), affording > 90% 1 O 2 selectivity. Long-term continuous-flow experiments and life-cycle assessments highlight the potential for scalable water treatment. Our work deciphers how coordination structure governs reactive oxygen species, providing a universal design paradigm for metal-pyridinic N 4 catalysts. Download: Download high-res image (210KB) Download: Download full-size image