Nitrate Chemodenitrification by Iron Sulfides to Ammonium under Mild Conditions and Transformation Mechanism.

Autotrophic denitrification utilizing iron sulfides as electron donors has been well studied, but the occurrence and mechanism of abiotic nitrate (NO) chemodenitrification by iron sulfides have not yet been thoroughly investigated. In this study, NO chemodenitrification by three types of iron sulfides (FeS, FeS, and pyrrhotite) at pH 6.37 and ambient temperature of 30 °C was investigated. FeS chemically reduced NO to ammonium (NH), with a high reduction efficiency of 97.5% and NH formation selectivity of 82.6%, but FeS and pyrrhotite did not reduce NO abiotically. Electrochemical Tafel characterization confirmed that the electron release rate from FeS was higher than that from FeS and pyrrhotite. Quenching experiments and density functional theory calculations further elucidated the heterogeneous chemodenitrification mechanism of NO by FeS. Fe(II) on the FeS surface was the primary site for NO reduction. FeS possessing sulfur vacancies can selectively adsorb oxygen atoms from NO and water molecules and promote water dissociation to form adsorbed hydrogen, thereby forming NH. Collectively, these findings suggest that the NO chemodenitrification by iron sulfides cannot be ignored, which has great implications for the nitrogen, sulfur, and iron cycles in soil and water ecosystems.