Photo-Catalytic Reduction of Nitrate by Ag-TiO2/Formic Acid Under Visible Light: Selectivity of Nitrogen and Mechanism

Ubiquitous nitrate (NO3−) in groundwater sources is considered a hazard compound for human health. Photo-catalytic reduction by Ag-TiO2/formic acid/visible light represents an emerging method for NO3− removal without secondary pollution. In this contribution, the removal of NO3− by photo-catalytic reduction and the selectivity of N2 were systematically investigated under varied conditions, including concentrations of Ag-TiO2, NO3−, and formic acid (HCOOH). The removal efficiency of NO3− reached 84.47%, 82.68% of which was converted to N2 under the optimal conditions: NO3− at 50 mg-N/L, Ag-TiO2 at 1.0 g/L, HCOOH at 20.05 mmol/L, and reaction time at 120 min. The removal of NO3− was enhanced mainly by CO2− rather than by photo-generated electrons or HCOO−. The results of this study indicated that the production of ·CO2− by Ag-TiO2 and HCOOH under visible light catalysis can achieve efficient NO3− removal.