Asymmetric Coordination Modulating Co Spin State for Peroxymonosulfate Activation to Accelerate 1O2 Generation

Abstract

Singlet oxygen (1O2) has received extensive attention for the selective degradation of emerging contaminants. However, how to efficiently generate 1O2 by modulating the asymmetric structure and electron spin state of catalyst remains a challenge. Herein, an asymmetric Fe─S─Co structured catalyst (Co-Fe3S4) is designed by in situ substitution of FeIIITd strategy. The strong interaction in the asymmetric structure induces a low-spin state (e: ↑↓, ↑↓, t2: ↑↓, _, _) at d-orbital of Co sites, shifting the d-band center closer to the Fermi level and elevating the antibonding states, which is beneficial for the adsorption of peroxymonosulfate (PMS). The catalyst accelerates 1O2 generation by PMS activation, achieving 100% removal of acetaminophen in pharmaceutical wastewater in 8 min with a high K-value of 112 min⁻¹ M⁻¹. Experiments and DFT calculations reveal that the spin state of the generated *O2 (from the S─O bond cleavage in HSO5−) is reduced by electron reversal (↓ to ↑) or pairing (↑, ↑ to ↑↓, _) in the 2p (2px and 2py) orbitals of the O─O anti-π bond (π*), resulting in the 1O2 generation. This work presents an approach for regulating the spin state using an asymmetric structure and offers a broader perspective on the generation mechanism of 1O2.