Selective photo-reduction of nitrate to nitrogen with a two-step process by a KBH 4 /Cu(II) modified CuFe 2 O 4 photocatalyst

Nitrate (NO 3 − ) removal by photochemical-reduction has received extensive attention. However, the low selectivity of NO 3 − reduction to N 2 hinders the application of this technology. In this study, a novel Cu@Fe-Cu-CuFe 2 O 4− x photocatalyst was prepared by modifying CuFe 2 O 4 with KBH 4 and Cu(II), and used to selectively reduce NO 3 − to N 2 with a two-step reduction process. In step (1), with Cu@Fe-Cu-CuFe 2 O 4− x /ultraviolet (UV) system, 91.0% NO 3 − was reduced to 52.3% NO 2 − and 39.4% N 2 within 60 min. The rapid removal of NO 3 − was due to the synergistic effect of oxygen vacancies, Fe-Cu corrosion cell, and CuFe 2 O 4 photocatalysis. In step (2), H 2 C 2 O 4 and H 2 O 2 were introduced into the effluent of step (1) to promote CO 2 · − formation via Fe(II) and Fe(III) catalysis and UV radiation, which boosted the selective reduction of NO 2 − to N 2 . When H 2 C 2 O 4 and H 2 O 2 dosages were both 4.0 mmol·L −1 and the reaction time was 30 min, the removal efficiency of NO 2 − achieved 100% and the selectivity of N 2 was 83.0%. Overall, the two-step reduction process achieved 95.0% NO 3 − removal efficiency and 90.1% N 2 selectivity with initial NO 3 − concentration of 30 mg·N·L −1 . In addition, the denitrification mechanism of the two-step reduction process was tentatively proposed.