Selective reduction of nitrate into nitrogen at neutral pH range by iron/copper bimetal coupled with formate/ferric ion and ultraviolet radiation

Nitrate reduction by zero valent iron (Fe-0) has been gained increasing attention. However, two key issues, that is, the reduction is efficient only at acidic condition; and the major reduction product is ammonium, which limited the application of Fe-0 for the nitrate removal. In this study, to address these issues, a novel system of Fe-0@Cu-0 bimetal with formate/Fe3+ under UV irradiation was developed for the nitrate reduction. The results showed that 100% nitrate removal efficiency and 98% N-2 selectivity were achieved at initial pH of 6.47 by a two-step reduction process: (1) the nitrate was firstly reduced to nitrite, while ammonium was negligible in the Fe-0@Cu-0/formate/UV system; (2) the accumulated nitrite in the effluent from the first-step reduction could be further reduced to nitrogen by CO2 center dot(-) radical generated by the reaction of formic acid, Fe3+ and UV radiation. Almost no formate residual was found in the effluent due to the action of photo-induced electron transfer of Fe3+. The optimization of operation conditions and the combination mode of Fe-0@Cu-0 with formate/formic acid, Fe3+ and UV were investigated. The chemical denitrification mechanism of the Fe-0@Cu-0 particles was proposed.