Enhancing Efficiency and Selectivity of Nitrate Reduction Toward Nitrogen Gas in an Open-Air UV/Fe(III)–Oxalate System

An advanced photochemical reduction system involving the UV/Fe(III)–oxalate system was developed for the reduction of nitrate (NO3−) to harmless N-gaseous species, primarily nitrogen (N2), by carbon dioxide radical (·CO2−) generated in the presence of dissolved oxygen (DO). Electron paramagnetic resonance (EPR) analyses confirmed the presence of both ·CO2− and ·OH radicals. Systematic investigations were conducted on various operational parameters, such as the initial Fe(III) concentration, oxalate concentration, and pH levels, to assess their impacts on the efficiency and products of NO3− reduction. Notably, solution pH played a significant role in influencing the NO3− reduction efficiency and the final products. At pH 2, approximately 75% of NO3− was converted into N2 with an 80% selectivity. In the pH range of 3 to 5, a remarkable NO3− removal rate of about 90% was achieved. Furthermore, higher concentrations of Fe(III) (2 mM) and oxalate (10 mM) were found to enhance NO3− removal to 91.95% and 88.71%, respectively. The presence of DO increased the oxidative potential in the reaction system, subsequently enhancing the selectivity conversion of NO3− to N2. In summary, the UV/Fe(III)–oxalate system exhibits significant potential for effective removal of NO3− while achieving high selectivity for the production of N2 in water remediation applications.