Ultrahigh-loading Cu single atom catalysts enabled by nitrogen vacancies-anchored unsaturated Cu-N3 sites for singlet oxygen-dominated Fenton-like degradation

Ultrahigh-loading Cu single atoms (26.93 wt%) are atomically dispersed on g-C 3 N 4 via nitrogen vacancy anchoring. • Nitrogen vacancies act as electron reservoirs to accelerate the Cu(I)/Cu(II) redox cycling and H 2 O 2 activation. • A non-radical pathway dominated by Singlet oxygen( 1 O 2 ) is established via surface-mediated O 2 •⁻ disproportionation. • The catalyst overcomes traditional Fenton limitations and degrades tetracycline efficiently over a pH range of 7.68-11.33. The practical application of single-atom catalysts (SACs) in advanced oxidation processes (AOPs) for wastewater treatment is severely constrained by their limited metal loading. Herein, we report the synthesis of an ultrahigh-loading copper single-atom catalyst (SA-Cu/g-C 3 N 4 ) via a supramolecular pre-assembly strategy coupled with a two-step thermal polycondensation. The resulting catalyst achieved an exceptionally high Cu loading of 26.93 wt% with maintaining atomic dispersion, as confirmed by aberration-corrected electron microscopy and X-ray absorption fine structure spectroscopy. Structural analyses revealed that isolated Cu(I) species are stabilized as coordinatively unsaturated Cu(I)–N 3 moieties adjacent to nitrogen vacancies (NVs). In Fenton-like degradation of tetracycline, SA-Cu/g-C 3 N 4 attains 86.4% removal within 60 min and sustains high catalytic activity across a broad pH range. Mechanistic investigations demonstrated that NVs act as localized electron reservoirs to accelerate the Cu(I)/Cu(II) redox cycle, while the Cu(I)–N 3 sites facilitate the selective conversion of H 2 O 2 to singlet oxygen ( 1 O 2 ) via a surface-mediated superoxide disproportionation pathway. Consequently, a non-radical oxidation regime dominated by 1 O 2 is established, enabling efficient pollutant degradation with enhanced selectivity and stability. This work not only provides a viable strategy for constructing high-loading SACs but also deepens the mechanistic understanding of vacancy-engineered non-radical AOP systems for environmental remediation. Download: Download high-res image (236KB) Download: Download full-size image