LAUSR

Abstract Although photocatalytic reduction of nitrate attracted much attention recently, undesired intermediate products (nitrite and ammonium) limited its application in practice. In this study, novel Pd/GdCrO3 composite was successfully synthesized to photo-catalytically reduce nitrate to N2 with high selectivity. Compared with TiO2 (P25), GdCrO3, Ag/GdCrO3 and Cu/GdCrO3, 1 wt% Pd/GdCrO3 achieved higher removal rate of nitrate (98.7%) and selectivity to N2 (100%). The kinetics constant of 1 wt% Pd/GdCrO3 was two times higher than that of P25. Even after six cycling runs, 1 wt% Pd/GdCrO3 still remained high photocatalytic reduction rate of nitrate (95.5%) and selectivity to N2 (98.4%). Such advantages were not only attributed to the negative conduction band value of GdCrO3 but also attributed to the co-catalyst effect of Pd. On one hand, nano particles Pd improved the utilization of charge carriers of GdCrO3. On the other hand, nitrite was easily reduced to NO* on nano particles Pd surface, followed by decomposition step to N* and O*, and then the reduction of nitrite in the vicinity of the N* could yield N2O* which would be preferentially transformed into N2. Accordingly, high concentration of nitrite accumulated initially could enhance the likelihood of N* encountering nitrite so as to increasing the N2 selectivity. In addition, electron paramagnetic resonance and hole scavenger experiments demonstrated that both photo-generated electrons and CO2 − played important role in photocatalytic reduction process, suggesting a different mechanism from P25 where nitrate was mainly reduced by CO2 −. Thus, the present work not only prepared a promising photocatalyst for reduction of nitrate in water/wastewater treatment process, but also provided a simple and efficient way to improve the photocatalytic activity and selectivity to N2of photocatalysts.