Selective conversion of nitrate to nitrogen gas by enhanced electrochemical process assisted by reductive Fe(II)-Fe(III) hydroxides at cathode surface

Abstract

A selective electrocatalytic system for the exhaustive conversion of inorganic nitrogen to nitrogen gas (N2) is developed, whereby the total nitrogen (TN) removal and N2 selectivity achieve 96.8 % and 99.6 % in 120 min, respectively. Cyclic voltammetry reveals the feasibility of electrooxidative chlorination of NH4+ compared to direct anodic oxidation. The TN removal is ranging from 96.2% to 99.7% under various inorganic nitrogen ratios. Green rust (GR) of mixed Fe(II)-Fe(III) hydroxides is identified at cathode surface by in-situ Raman analysis, donating electrons to NO3−. Direct electron reduction, indirect atomic H* reduction, and GR induced reduction are integrated for the rapid NO3− conversion at cathode interface. Treatment of authentic wastewater of nickel plating in continuous running further demonstrates the superiority and durability of the electrochemical system for both NO3− and TN abatement. The electrochemical system has potential for efficient and stable nitrogen pollutants removal in the high-salinity wastewater.