Graphical Abstract
![](https://wqketang.oss-cn-beijing.aliyuncs.com/unzip/large-zip/zip-2a02756c-9a3e-46eb-b900-8aa2a7a59dfe/5696/files/5696-TOC.jpg?Expires=1725758032&OSSAccessKeyId=STS.NT5eViCkqzTYdbfdqxMkjpyyq&Signature=jY3j%2B7hA41plIj%2B9zgKNzyBHMuc%3D&security-token=CAISywJ1q6Ft5B2yfSjIr5eALuzdrrRQzZayZkTXgHEtQeRGn7zSkzz2IHtKenhsBOsbtfk1mG5W5%2FgZlqJ9SptIAEfJa9d99MzUP%2FpFltCT1fau5Jko1beHewHKeTOZsebWZ%2BLmNqC%2FHt6md1HDkAJq3LL%2Bbk%2FMdle5MJqP%2B%2FUFB5ZtKWveVzddA8pMLQZPsdITMWCrVcygKRn3mGHdfiEK00he8TouufTinpHMskGA1Aell7Mvyt6vcsT%2BXa5FJ4xiVtq55utye5fa3TRYgxowr%2Fwo0v0YpGya5YzHXwcPskvdKZbo78UqLQlla6w%2BGqFJqvPxr%2Fp8t%2Fx5fWJKAezhVgs8cVM8JOjIqKOscIsiJsO71SmqFV55c8Fdm%2BgUooJVgIMhTnduUfAPJAGOxzJitP%2BUVGGphr60TEnBL4rB5MUctfzRp75SXVPUTzDnGoABjuNLcf76FQN6p3t%2BSlCg%2FxR5C72RIk78k%2BUi44L9ZBmFT6F8GV7aXA52D1Ps56knKF6PAnhRivwyTxgsolycBfvccb3t5jGJ24SgY0aYosAECutxAo7sJhSwlwZvGwGDZJsop1vGiZ8eN1MbtZeRRuMeaZ2I%2BQo%2BnVP6Cf%2F0pDsgAA%3D%3D)
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Nitrate (NO3−) removal by photochemical-reduction has received extensive attention. However, the low selectivity of NO3− reduction to N2 hinders the application of this technology. In this study, a novel Cu@Fe-Cu-CuFe2O4−x photocatalyst was prepared by modifying CuFe2O4 with KBH4 and Cu(II), and used to selectively reduce NO3− to N2 with a two-step reduction process. In step (1), with Cu@Fe-Cu-CuFe2O4−x/ultraviolet (UV) system, 91.0% NO3− was reduced to 52.3% NO2− and 39.4% N2 within 60 min. The rapid removal of NO3− was due to the synergistic effect of oxygen vacancies, Fe-Cu corrosion cell, and CuFe2O4 photocatalysis. In step (2), H2C2O4 and H2O2 were introduced into the effluent of step (1) to promote CO2·− formation via Fe(II) and Fe(III) catalysis and UV radiation, which boosted the selective reduction of NO2− to N2. When H2C2O4 and H2O2 dosages were both 4.0 mmol·L−1 and the reaction time was 30 min, the removal efficiency of NO2− achieved 100% and the selectivity of N2 was 83.0%. Overall, the two-step reduction process achieved 95.0% NO3− removal efficiency and 90.1% N2 selectivity with initial NO3− concentration of 30 mg·N·L−1. In addition, the denitrification mechanism of the two-step reduction process was tentatively proposed.
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