Selective reduction of nitrate to nitrogen gas by novel Cu2O-Cu0@Fe0 composite combined with HCOOH under UV radiation

The nitrate reduction by Fe-based materials has been extensively studied, however, the selectivity of nitrate reduction to nitrogen gas is very low, which hinders the application of this technology. In this study, a novel Cu2O-Cu-0@Fe-0 composite was synthesized and a strategy of Cu2O-Cu-0@Fe-0 composite combined with HCOOH under UV radiation as reducers for the nitrate reduction was established to improve the selective reduction of nitrate (NO3-) to nitrogen gas (N-2). The Cu2O-Cu-0@Fe-0 composite was synthesized by simple chemical replacement and O-2 oxidation process and characterized by SEM, EDS, XRD and XPS. The nitrate removal efficiency of 100% and the N-2 selectivity of 95.4% were achieved in Cu2O-Cu-0@Fe-0/HCOOH/UV system when the initial nitrate concentration was 50 mg N/L and the reduction time was 60 min. The nitrate reduction efficiency was low by the role of alone or combinations of Cu2O-Cu-0@Fe-0 composite, HCOOH or UV radiation. The quick reduction of nitrate to nitrite was due to the synergistic effect of electrons from the galvanic-type cell consisting of Fe-0 as anode and Cu-0 as cathode, photoelectrons from Cu2O under UV radiation and CO2 center dot- produced mainly via photochemical reaction between HCOOH and UV radiation. The subsequent conversion of nitrite to N-2 was caused by CO2 center dot-, which was responsible for the high efficient reduction of nitrate to nitrogen gas in the Cu2O-Cu-0@Fe-0/HCOOH/UVsystem. Finally, the denitrification mechanism of the Cu2O-Cu-0@Fe-0/HCOOH/UV system was tentatively proposed.