Air oxidation behavior of wet-mechanochemically synthesized pyrite FeS2: Fenton performance regulated by Fe species, sulfur vacancy and crystal facet ratio

Numerous studies have revealed that air oxidation behavior profoundly impacts pyrite properties. Whereas its influence on pyrite Fenton performance remains controversial. Herein, pyrite FeS 2 nanoparticles synthesized by facile wet-mechanochemical method was employed as oxidation model and its oxidation degree was evaluated by XPS depth profiling technique. Based on theoretical calculation and experimental evidence, the properties and Fenton performance of surface oxidized pyrite (SOP x ) were comprehensively assessed. With oxidation degree increase, free radical generation selectivity was alternated from •O 2 – to •OH, and the selectivity to •OH showed strong correlations with {210} facet ratio, Fe(Ⅱ)-O and sulfur vacancies (SVs) contents. The oxidation degree dependence in •OH selective production primarily stemmed from different electron-donating and Fe 2+ releasing capacity. Moderately oxidized pyrite (SOP 4 ) with high {210} facet ratio, SVs and Fe(Ⅱ)-O contents could donate electrons for H 2 O 2 barrierless dissociation and Fe 2+ /Fe 3+ redox-cycle, and cause more Fe 2+ releasing to enhance homogeneous Fenton reaction. As the oxidation degree increased (from SOP 0 to SOP 4 ), the Fenton systems demonstrated a significant enhancement in sulfadiazine (SDZ) degradation kinetics, with the rate constant increasing from 0.02039 to 0.06904 min −1 . The superior SDZ removal efficiency in SOP 4 system at wide pH range (5–9) indicated moderate oxidation significantly improved its decontamination and practical application ability. However, the amorphous iron oxide layer generated in the over-oxidized pyrite (SOP 6 ) impaired its catalytic activity, resulting in a decrease of the rate constant (0.0485 min −1 ). These findings unveiled the mystery of Fenton performance regulated by FeS 2 oxidation via {210} facet, SVs and Fe(Ⅱ)-O, and offered fresh insights into developing targeted structures for tunable performance.