Peroxymonosulfate activation by iron-cluster-modified Mn single atom catalyst for ciprofloxacin removal: Non-radical pathway dominated by 1O2 and high-valent metal–oxygen species

Abstract

Atomic clusters have been recognized for boosting interactions with single-atom sites and activating peroxymonosulfate (PMS) to degrade pollutants. However, research on the synergies between different metals in these clusters and their impact on enhancing single-atom activity remains limited. This paper introduces an iron-cluster-modified manganese single-atom catalyst (FeMn_ac-NC) exhibiting exceptional catalytic activity. At low doses of the catalyst (FeMn_ac-NC, 0.05 g/L) and the oxidant (PMS, 0.2 g/L), the FeMn_ac-NC/PMS system recorded an impressive removal efficiency of 91.0 % in 5 min, exhibiting a k_obs of 0.1038 min⁻¹. Within this system, the active oxygen species identified included singlet oxygen and high-valent metal–oxygen species. X-ray photoelectron spectroscopy analysis revealed a significant presence of pyrrolic nitrogen in the material, which binds with Mn to create the primary active site. Based on calculations using the density functional theory, the redox cycling between iron clusters and manganese single atoms has been proved to improve the activation efficiency of the system. The system demonstrates high tolerance to environmental media containing anions and dissolved organic matter, showing notable degradation performance over a wide pH range. This research provides valuable insights for the development of high-performance catalysts that is well-suited for practical environmental purification applications.