Facet-Dependent Productions of Reactive Oxygen Species from Pyrite Oxidation

Reactive oxygen species (ROS) are widespread in nature and play central roles in numerous biogeochemical processes and pollutant dynamics. Recent studies have revealed ROS productions triggered by electron transfer from naturally abundant reduced iron minerals to oxygen. Here, we report that ROS productions from pyrite oxidation exhibit a high facet dependence. Pyrites with various facet compositions displayed distinct efficiencies in producing superoxide (O₂^• -), hydrogen peroxide (H₂O₂), and hydroxyl radical (^•OH). The 48 h ^•OH production rates varied by 3.1-fold from 11.7 ± 0.4 to 36.2 ± 0.6 nM h^-1, showing a strong correlation with the ratio of the {210} facet. Such facet dependence in ROS productions primarily stems from the different surface electron-donating capacities (2.2-8.6 mmol e^- g^-1) and kinetics (from 1.2 × 10^-4 to 5.8 × 10^-4 s^-1) of various faceted pyrites. Further, the Fenton-like activity also displayed 10.1-fold variations among faceted pyrites, contributing to the facet depedence of ^•OH productions. The facet dependence of ROS production can greatly affect ROS-driven pollutant transformations. As a paradigm, the degradation rates of carbamazepine, phenol, and bisphenol A varied by 3.5-5.3-fold from oxidation of pyrites with different facet compositions, where the kinetics were in good agreement with the pyrite {210} facet ratio. These findings highlight the crucial role of facet composition in determining ROS production and subsequent ROS-driven reactions during iron mineral oxidation.