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.

尽管近来光催化还原硝酸盐备受关注，但不良的中间产物（亚硝酸盐和铵盐）限制了其在实践中的应用。在这项研究中，成功地合成了新型的Pd / GdCrO ₃复合材料，以高选择性将光硝酸盐还原为N ₂。与TiO ₂（P25），GdCrO ₃，Ag / GdCrO ₃和Cu / GdCrO _3相比，1 wt％Pd / GdCrO ₃获得更高的硝酸盐去除率（98.7％）和对N _2的选择性（100％）。1wt％的Pd / GdCrO ₃的动力学常数是P25的动力学常数的两倍。即使经过六次循环运行，Pd / GdCrO _3的含量仍为1 wt％仍然保持较高的硝酸盐光催化还原率（95.5％）和对N _2的选择性（98.4％）。这样的优点不仅归因于GdCrO ₃的负导带值，而且归因于Pd的助催化剂作用。一方面，纳米颗粒Pd提高了GdCrO ₃的电荷载流子的利用率。另一方面，亚硝酸盐在纳米粒子Pd表面容易还原为NO *，然后分解为N *和O *，然后在N *附近还原亚硝酸盐可生成N ₂ O *，优先转化为N ₂。因此，最初累积的高浓度的亚硝酸盐可增加N *遇到亚硝酸盐的可能性，从而增加N _2的选择性。此外，电子顺磁共振和空穴清除剂实验表明，光生电子和CO _2-均在光催化还原过程中起着重要作用，暗示了与P25不同的机理，在P25中硝酸盐主要被CO _2-还原。因此，本发明不仅制备了用于水/废水处理过程中还原硝酸盐的有前途的光催化剂，而且提供了一种简单有效的方法来提高光催化剂的光催化活性和对N ₂的选择性。