Preparation And Nitrogen Photofixation Of Pd/BiOBr And Fe-BiOCl Photocatalysts

Solar photocatalytic nitrogen fixation is an effective method to convert nitrogen to ammonia under mild conditions.The core is to develop high-efficient catalytic materials to improve the adsorption and activation of nitrogen.BiOX?Cl,Br,I?semiconductor photocatalytic materials possesses good photocatalytic activity due to their unique layered structure and electronic properties.However,the nitrogen fixation yield of the semiconductor photocatalytic materials cannot meet the demand.Therefore,it is critical that how to maintain good photocatalytic activity while enhancing the active site to increase the adsorption and activation ability of nitrogen over the semiconductor photocatalytic materials.The way of coordination of metal ions to activate the strong N?N triple bond is promising.The photocatalytic nitrogen fixation will be enhanced by effectively promoting the separation of photogenerated carriers and providing more nitrogen adsorption and activation sites.Therefore,in this paper,precious metal Pd and non-precious metal Fe is introduced by rational design to improve the capacity of nitrogen adsorption and activation over BiOX?X=Br,Cl?.The specific research contents are focused on the aspects:?1?BiOBr containing EG on the surface was used as a carrier,we successfully fabricated an atomically dispersed Pd catalyst over the BiOBr with UV-Vis under mild conditions,that is 0.2 Pd/BOB-EG catalyst.The structure,morphology,optical properties,formation mechanism of catalyst,differential charge density,and adsorption energy of nitrogen were analyzed by XRD,SEM,TEM,XPS,in situ FT-IR and density functional theory calculation?DFT?.The photocatalytic nitrogen fixation performance of the prepared samples was evaluated by nitrogen fixation experiments under simulated solar irradiation.The experimental results show that the synthesized atomically dispersed 0.2 Pd/BOB-EG catalyst exhibits high catalytic activity in photocatalytic nitrogen fixation at a rate of 124.63?mol·h^-1,exceeding that of0.2 Pd/BOB-H₂O catalyst with Pd nanoparticles by a factor of 1.17.The calculation results clarify the importance of EG during the progress of atomically dispersed Pd catalyst and the mechanism of Pd-EG group in the activation of N?N triple bond.Finally,the photocatalytic nitrogen fixation mechanism of nano-particles and atomically dispersed Pd catalysts was proposed.?2?A series of Fe-BiOCl photocatalysts with different contents were synthesized by hydrothermal method.The photocatalytic performance of various catalysts was evaluated based on photocatalytic nitrogen fixation experiments.Through photocatalytic nitrogen fixation experiments and various characterization experiments,the following conclusions were obtained.Fe₂O₃is observed over 5wt%Fe-BiOCl catalyst,which means Fe is present in the form of Fe₂O₃.While Fe is existed in the form of trivalent iron over10wt%Fe-BiOCl and 15wt%Fe-BiOCl catalysts with the way of doping.The results of photocatalytic nitrogen fixation experiments show that the formation rate of 10wt%Fe-BiOCl NH₄⁺is 30?mol/L,which is higher than other photocatalytic materials.The results show that the main reason for the enhanced activity is that the presence of Fe,which reduces the forbidden band width and improves the photo-responsibility of the catalyst.On the other hand,Fe doping can provide more reactive sites for photocatalytic nitrogen fixation,and thus improve the formation rate of NH₄⁺.