Surface vacancy structure of iron sulfide critical to nitrogen transformation during denitrification

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 in nitrate transformation remains unclear. Here we show that pyrrhotite with iron vacancies and a low Fe–S bond energy (1.35 eV) facilitates efficient electron transfer and microbial utilization of reduced sulfur to convert nitrate into dinitrogen. Conversely, FeS₂, with strong Fe–S bonding (1.63 eV), shows minimal reactivity due to restricted electron mobility. FeS, with an intermediate bond energy (1.39 eV) and abundant sulfur vacancies, supports simultaneous abiotic nitrate-to-ammonium and microbial nitrate-to-dinitrogen conversions. These mineral-specific mechanisms regulate nitrogen transformations in anoxic systems such as wetlands and marine sediments, ultimately shaping global nitrogen cycling. Furthermore, tuning iron sulfide phases and vacancy structures offers potential strategies for sustainable wastewater treatment, steering nitrate removal towards nutrient recovery or benign dinitrogen production.