Surface Vacancies in Iron Sulfides Drive Denitrification Mechanisms

Global nitrogen cycling is tightly governed by iron and sulfur biogeochemical processes in anoxic environments, while the mechanism of surface vacancy structures of iron sulfides on nitrate transformation remains unclear. This research demonstrated that pyrrhotite with iron vacancies and lower Fe–S bond energy (1.35 eV) facilitated efficient electron transfer and microbial utilization of reduced sulfur to achieve nitrate autotrophic denitrification to dinitrogen. Conversely, FeS2, possessing strong Fe–S bonding (1.63 eV), showed minimal reactivity due to restricted electron mobility. FeS, with intermediate bond energy (1.39 eV) and abundant sulfur vacancies, supported simultaneous abiotic nitrate–to–ammonium conversion and microbial denitrification. These mineral-specific mechanisms support nitrogen transformations in diverse anoxic systems, from wetland to marine sediments, ultimately determining the global nitrogen cycling. Furthermore, tuning iron sulfide phases and vacancy structures presents novel strategies for sustainable, wastewater treatment, steering nitrate removal toward nutrient recovery or benign gas production.