Cobalt doping of FeS2 simultaneously promotes radical and nonradical pathways of O2 activation by creating dual active sites

Abstract

Molecular oxygen (O₂) activation by iron-based materials represents a sustainable strategy for organic pollutant removal. However, the inherently high energy barrier of O₂ activation limits the generation of reactive species, especially nonradical species. Here, we demonstrate that cobalt (Co) doping of pyrite (FeS₂) significantly enhances both radical and nonradical pathways of O₂ activation by creating dual active sites. Specifically, quenching experiments and theoretical calculation demonstrate that the Fe atoms are the primary sites of hydroxyl radical (·OH) generation. Co doping upshifts the Fe d-band center toward the Fermi level (from −2.02 to −1.63 eV), thereby facilitating ·OH generation. Simultaneously, electron paramagnetic resonance spectroscopy results indicate that Co doping promotes generation of sulfur vacancies (SVs), which act as singlet oxygen (¹O₂)-producing sites. The divergent O₂ transformation pathways at the Fe and SVs sites are attributed to differences in adsorption affinity of *OOH intermediate at these sites. The relative contributions of the two pathways can be tuned by varying the Co dopant level, enabling efficient degradation of diverse contaminants, including chlorinated phenols, chlorinated aliphatic hydrocarbons, and antibiotics. This work elucidates a dual-site catalytic mechanism for regulation of radical and nonradical pathways of O₂ activation, and can guide the design of O₂-activating materials for environmental remediation via advanced oxidation processes.