A novel strategy for sequential reduction of nitrate into nitrogen by CO2 anion radical: Experimental study and DFT calculation

Wang, Bingqing; An, Baohua; Su, Zhi; Li, Laicai; Liu, Yong

A novel strategy for sequential reduction of nitrate into nitrogen by CO2 anion radical: Experimental study and DFT calculation

2021

Wang, Bingqing | An, Baohua | Su, Zhi | Li, Laicai | Liu, Yong

In order to expand the application of CO₂ anion radical (CO₂⁻), as a novel green reductant in the control of environmental pollution, CO₂⁻ radical was induced into the reduction of nitrate. The reduction efficiency, products and mechanism of nitrate or nitrite by CO₂⁻ radical were investigated based on the results of batch experiments and theoretical calculation using density functional theory (DFT) methods, respectively. It was found that: (1) the efficiency of nitrate reduction by CO₂⁻ radical from the HCOOH/UV system was far lower than that of nitrite under the same reaction conditions, (2) the rate-control step of nitrate reduction by CO₂⁻ radical was the transformation process of nitrate into nitrite with an activation energy of 23.9 kcal/mol, (3) the final products of nitrate reduction were mainly composed of nitrogen (N₂). On this basis, a novel strategy of rapid reduction of nitrate into N₂ using CO₂⁻ radical was proposed. Specifically, nitrate was firstly reduced into nitrite with the assistance of Zn/Ag bimetal, and then nitrite was further reduced into N₂ by CO₂⁻ radical. In this way, the removal efficiency of nitrate was all achieved nearly 100% in the initial nitrate concentration ranging from 25 to 100 mg (N)/L, while the highest N₂ selectivity could reach 97.5%. This work provided a promising approach for the reduction of nitrate into nitrogen with high efficiency and high N₂ selectivity by CO₂⁻ radical.

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