Selective reduction of nitrate to nitrogen by Fe0-Cu0-CuFe2O4 composite coupled with carbon dioxide anion radical under UV irradiation

Zero-valent iron (Fe-0) has been widely used for the reduction of nitrate, but the end reduction product is mainly ammonium. Here, a novel strategy for selective reduction of nitrate (NO3-) to nitrogen gas (N-2) with high efficiency and N-2 selectivity was investigated using Fe-based material (Fe-0-Cu-0-CuFe2O4) combined with citric acid (CA) and ultraviolet (UV) irradiation. In this strategy, the nitrate was firstly reduced to nitrite (NO2-) by Fe0-Cu-0-CuFe2O4/UV process, and then the produced NO2- could be further reduced to N-2 by carbon dioxide anion radicals (CO2 center dot-) which was generated from CA that was added later. In this process, the selective reduction of NO3- to NO2- was a key step. For this purpose, we synthesized Fe-0-Cu-0-CuFe2O4 composite by simple chemical replacement and in-situ growth process, which made it have a delicate structure with good contact between Cu and Fe and CuFe2O4. The selective reduction of NO3- to NO2- in Fe-0-Cu-0-CuFe2O4/UV process was due to that the Cu-0 was the electron enrichment center and the photo-generated hole could suppress the NO3- reduction to NH4+ by Fe-2(+). In this proposed strategy, 100% NO3- removal efficiency and 96.3% N-2 selectivity were achieved when the initial NO3- concentration was 30 mg N/L and the reduction time was 60 min. The denitrification mechanism of the Fe-0-Cu-0-CuFe2O4/UV/CA system was proposed.

Automated summary

A novel strategy for the selective reduction of nitrate to nitrogen gas with high efficiency and selectivity has been investigated using a Fe-based material combined with citric acid and UV irradiation. The proposed strategy achieved 100% nitrate removal efficiency and 96.3% nitrogen gas selectivity, and a denitrification mechanism was proposed.