Preparation Of TiO₂-based Composite And Exploration Of Their Photocatalytic Nitrogen Fixation Performance

As a promising energy storage and conversion technology,solar nitrogen fixation technology,which converts abundant and stable N₂into NH₄⁺,has attracted wide attention.As an important raw material for energy development,chemical preparation and fertilizer production,ammonia is very important to human life.Herein,TiO₂is chosen as the primary catalyst because it is one of the most promising catalytic materials for practical application.Using TiO₂as photocatalytic nitrogen fixing material,the synergistic effect of Au and PdO and the influence of supporting sequence on the photocatalytic nitrogen fixing activity of TiO₂were studied,the new idea of Cu improving the photocatalytic nitrogen fixing performance of TiO₂was discussed,and the influence of PdO on the relative photocatalytic nitrogen fixing performance of TiO₂crystal was explored.（1）Both PdO and Au both have the ability to improve the photocatalytic nitrogen fixing activity of TiO₂.PdO improves the photocapturing ability of the composites,and Au can be used as the electron transfer medium.However,there are relatively few studies on whether the loading sequence can affect the photocatalytic nitrogen fixing performance of the composites.In the nitrogen fixation reaction,PdO/Au-TiO₂showed higher photocatalytic nitrogen fixation performance（198.35 mg/L）compared with Au/PdO-TiO₂,mainly because the loading sequence of Au and PdO on TiO₂had a significant effect on the electron transport pathway,and the carrier recombination efficiency of PdO/Au-TiO₂was lower.Charge transfer ability is better because of its better photocatalytic nitrogen fixing activity.Furthermore,the possible photocatalytic nitrogen fixation mechanism of PdO/Au-TiO₂was proposed.（2）The supporting metal Au and Pd can effectively promote the photocatalytic nitrogen fixing ability of TiO₂.Does the supporting transition metal Cu have the same effect?Using Na BH₄and ascorbic acid as reductant,M-TiO₂-S1 and M-TiO₂-S2（M=Au,Pd,Cu）were prepared respectively.Due to the synergistic effect of size effect,strong electron interaction,strong carrier separation ability and Cu/Cu²⁺can provide more active sites,Cu-TiO₂-S1 has the best photocatalytic nitrogen fixation performance.In addition,it was found that the nitrogen fixing performance of Au-TiO₂was different due to the different size of Au particles caused by different reductant.Cu particles could not be obtained by ascorbic acid reduction,so Cu-TiO₂-S2 had no activity.On the contrary,the catalytic performance and size of Pd-TiO₂were not affected by the reductant.Finally,the possible photonitrogen fixation reaction mechanism of Cu/Cu²⁺-TiO₂was proposed.（3）To explore the interaction between PdO and TiO₂with different crystalline phases,and reveal the nature of PdO/TiO₂to improve photocatalytic nitrogen fixation,and systematically study the difference in the performance of PdO/TiO₂（single-crystalline）and PdO/TiO₂（biphase）in photocatalytic nitrogen fixation reaction was studied.It is found that PdO/B-TiO₂has the best photocatalytic nitrogen fixation performance among single-crystalline TiO₂,which may be because the morphology,specific surface area and photogenerated carrier separation efficiency affect its photocatalytic activity.For biphase TiO₂,the photocatalytic nitrogen fixation performance of PdO/AB-TiO₂is significantly better than that of PdO/AR-TiO₂,possibly because the photocatalytic activity of PdO/AB-TiO₂is affected by the separation efficiency of photogenerated carrier and specific surface area.In addition,it was found that the nitrogen fixation performance of PdO/P25 and PdO/AB-TiO₂was very similar when PdO was loaded on P25.Finally,the possible photocatalytic N₂reduction mechanism of PdO/AB-TiO₂composites was proposed.