Efficient and selective photocatalytic nitrite reduction to N2 through CO2 anion radical by eco-friendly tartaric acid activation

In this study, the environmentally friendly precursor, tartaric acid (TA), was employed for the generation of CO2 anion radical (CO2•−) in an advanced UV/TA/Fe3+ system to reduce the hazardous NO2–-N in wastewater. To optimize this process, various factors, including the dosage of Fe3+, TA, and pH, were systematically investigated for their impact on the reduction process. Under the conditions of 3 mmol/L Fe3+ dosage, 10 mmol/L TA dosage, and a pH of 2.5, NO2–-N was effectively removed from the water within 60 min, selectively transformed into N2, with a remarkable N2 selectivity of 91.2%. In the optimal conditions, the NO2–-N reduction mechanism in the UV/TA/Fe3+ system and the critical role of CO2•− were illustrated. Finally, this study explored the reduction of real nitrified seawater using the UV/TA/Fe3+ system. The results demonstrated that the UV/TA/Fe3+ system could completely eliminate NO2–-N and achieve a N2 selectivity of up to 90%, with minimal interference from coexisting ions. This work holds promising implications for the environmentally benign treatment of nitrite-polluted wastewater.