Speciation Differences in the Surface Oxidizing Species on FeS<sub>2</sub>and NiS<sub>2</sub>: Reactivity in Hydrogen Atom Transfer and Oxygen Atom Transfer
Xuebin Zhang, Hao Tian, Song‐Hai Wu, Yong Liu, Xu Han
Abstract
As the most abundant metal sulfide on Earth’s surface, pyrite (FeS 2 ) plays important roles in the transformation of various elements and contaminants. Noteworthily, pyrite-type metal disulfides (FeS 2 and NiS 2 ) exhibit enzymatic reactivity in hydrogen atom transfer (HAT) and/or oxygen atom transfer (OAT) reactions. However, the oxidizing species and their corresponding reactivity on the surface of FeS 2 and NiS 2 are still not clear. In this work, both FeS 2 -O 2 and NiS 2 -O 2 exhibit high HAT reactivity, whereas only FeS 2 -O 2 shows OAT reactivity under alkaline and oxic conditions. The high conversion and selectivity in the oxidation of l -cysteine and benzyl alcohol to the respective l -cystine and benzaldehyde indicate the high HAT reactivity of the oxidizing species in both FeS 2 -O 2 and NiS 2 -O 2 systems. On the other hand, the higher oxidation selectivity of methyl phenyl sulfide (MPS) and methyl phenyl sulfoxide (PMSO) to the corresponding PMSO and phenyl methyl sulfone (PMSO 2 ) by FeS 2 -O 2 than those by NiS 2 -O 2 indicates that Fe(IV)═O oxo in the FeS 2 -O 2 system plays important roles in OAT reactions. EPR and quenching experiments reveal that superoxo, peroxo, and oxo species, instead of the produced •OH and H 2 O 2, are the predominant oxidants in HAT reactions, and the DPD and electrochemical analyses indicate that the oxidizing species are located on the surface of FeS 2 and NiS 2 . Raman analysis further confirms the presence of ≡Fe(III)-OOH peroxo and ≡Fe(IV)═O oxo on FeS 2 and ≡Ni(III)-OOH peroxo on NiS 2 . This study enriches our understanding on the reactivity of peroxo and/or oxo species on the surface of metal disulfides, providing new perspective for better understanding of the reactivity of various metal disulfides on the earth.