Efficient purification of a nitrate and chlorate mixture in water via photoredox activated intermediate...

Nitrate (NO₃^-) is a widespread contaminant that threatens human health and ecological safety. Meanwhile, the disinfection byproducts chlorate (ClO₃^-) is generated inevitably in conventional wastewater treatment. Therefore, the contaminants mixture of NO₃^- and ClO₃^- are universal in common emission units. Photocatalysis technology is a feasible approach for the synergistic abatement of contaminant mixture, where matching suitable oxidation reactions is a potential strategy to improve the photocatalytic reduction reactions. Herein, formate (HCOOH) oxidation is introduced to facilitate the photocatalytic reduction of the NO₃^- and ClO₃^- mixture. As a result, high purification efficiency of NO₃^- and ClO₃^- mixture are achieved, evidenced by 84.6% e^--dependent removal of the mixture at a reaction time of 30 min, with 94.5% N₂ selectivity and 100% Cl^- selectivity, respectively. Specifically, by the close combination of in-situ characterizations and theoretical calculations, the detailed reaction mechanism is revealed, in which the intermediate coupling-decoupling route from NO₃^- reduction and HCOOH oxidation is established by the chlorate-induced photoredox activation, leading to the significantly enhanced efficiency for the wastewater mixture purification. The practical application of this pathway is established for simulated wastewater to show its wide applicability. This work provides new insights into photoredox catalysis technology for its environmental application.