High selectivity for nitrogen in nitrate reduction on Ag–ZnO nanoparticles with formic acid as hole scavenger



A series of Ag-doped ZnO (Ag–ZnO) catalysts with a doping concentration up to 7wt% were prepared by a direct precipitation method. The prepared photocatalysts were characterized by XRD and TEM to determine their chemical composition and surface structure. The photocatalytic activity of different Ag–ZnO catalysts was evaluated in the photocatalytic reduction of nitrate in aqueous solution under UV illumination. In the experiments, formic acid was used as a hole scavenger to enhance the photocatalytic reduction reaction. The experimental results indicate that the presence of Ag in ZnO catalysts substantially enhances the photocatalytic reaction of nitrate reduction. It was found that the optimal dosage of 5wt%Ag in ZnO achieved the fastest reaction of nitrate reduction under the experimental condition. Nitrite ions were not monitored during the reaction and a negligible amount of ammonia formed. Hence selectivity to N2 is nearly 100%.