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 N-2 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 N-2 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 <middle dot>CO2- by Ag-TiO2 and HCOOH under visible light catalysis can achieve efficient NO3- removal.