Selective reduction of nitrate to nitrogen gas with hydrating electrons from the photo-corrosion of natural pyrite

The removal of nitrate (NO3−) from wastewater by photolysis has received increasing attention because the high photoactivity of NO3−. However, the relatively low efficiency and nitrogen gas (N2) selectivity remain challenges in denitrification. Herein, a novel strategy using in situ-generated hydrating electrons (eaq−) during the photo-corrosion of natural pyrite for enhancing the selective photochemical reduction of NO3− to N2 was proposed. The results indicated that the photo-corrosion of natural pyrite produced multitudinous reductive ions, such as Fe2+, S2− and S(IV) ions in aqueous solution, which served as the precursors of eaq− under ultraviolet irradiation (UV). The conduction band electrons on natural pyrite (ecb−) and pyrite promoted the regeneration of reductive ions, accelerating the production of eaq−. eaq− was identified as the predominant active species for the selective reduction of NO3− to N2 with high efficiency, which was verified by control, EPR and quenching tests. A NO3− removal efficiency of 98.07% and a N2 selectivity of 98.61% were achieved in the pyrite/UV/NO3− system at initial NO3− concentration of 30 mg N/L, pyrite dosage of 6 g/L, initial pH of 6. Finally, the denitrification mechanism of the pyrite/UV/NO3− system was tentatively proposed.