Oxygen Vacancy-Induced High-Spin Octahedral Co Sites Enable Accelerated Singlet Oxygen Production for Water Cleanup

Abstract

Spinel Co3O4 holds great promise for pollutant elimination in Fenton-like catalysis. Nevertheless, octahedral CoOh3+ sites with an intrinsic low-spin (LS) configuration deliver sluggish electron transport and cannot efficiently initiate the singlet oxygen (1O2)-dominated nonradical pathway. To address this issue, we develop an oxygen-vacancy-induced spin-state transition strategy in spinel Co3O4, where oxygen vacancies (Ov) distort octahedral CoOh-O coordination, lower crystal field splitting, and redistribute electrons to convert intrinsic LS CoOh3+ (t2g6eg0) into high-spin (HS) CoOh2+ (t2g5eg2) with occupied eg orbitals. This process constructs an Ov-HS CoOh2+ dual-site motif that spatially differentiates peroxymonosulfate activation: (i) Ov preferentially adsorbs PMS and polarizes the O–O bond of HSO5–. (ii) Adjacent HS CoOh2+ accelerates electron transfer through apex-to-apex eg orbital coupling, thereby promoting O–O bond cleavage, O* formation, and subsequent 1O2 generation. Inert ZnTd2+ and AlOh3+ site substitution experiments further verify that this Ov-HS CoOh2+ synergy, rather than isolated Ov or Ov-CoTd2+ sites, dominates selective 1O2 production. Consequently, Co3O4–Ov/PMS system achieves rapid Rhodamine B (RhB) elimination with a kinetic constant of 0.693 min–1 and a high 1O2 yield of 9.46 μmol, 24.9 and 5.5 times higher than pristine Co3O4, respectively. This work establishes Ov as a spin-state regulator and provides a dual-site cooperation strategy for designing nonradical oxidation catalysts.