Study On The Construction And Modification Of Bismuth And Bismuth Tungstate Composite Photocatalytic Nitrogen Fixation System

As one of the most common nitrogen-containing compounds,ammonia is an indispensable industrial product for human society.Nowdays,Haber-Bosch process is widely used to artificial synthesis ammonia in the industry,which causes energy waste and environmental pollution.Developing a new ammonia synthesis process to replace traditional nitrogen fixation process is the key of the development of human society.Among many new strategies,semiconductor photocatalytic nitrogen fixation technology is one of the most promising nitrogen fixation technologies because of the ability of directly utilize solar energy.bismuth tungstate is a common semiconductor material with chemical stability and suitable band gap,which is widely used to carry out photocatalytic process.However,its conduction band bottom is too low to reduce nitrogen.In this paper,the modification of bismuth tungstate was carried out by means of constructing preferred orientation structure and element dopingA bismuth tungstate photocatalyst with preferred orientation structure was prepared by microemulsion-solvent thermal coupling method.The results of SEM and TEM showed that the sample was uniform in morphology,which was characterized by a layered nano-disk structure with lamellar stacks assembled from nanoparticles.In the HRTEM test results,a 2:1 ratio of the interplanar spacing of the(131)crystal plane of the bismuth tungstate to the(024)crystal plane of the metal bismuth was observed.And the lattice fringes exhibited a certain regular orientation.The SAED pattern showed an arc shape,demonstrating the existence of a preferred orientation structure.The PL spectra demonstrate that the sample has a lower fluorescence intensity.The TRPL test results demonstrate that the preferred orientation of the material enhances its photo-generated carrier lifetime.The EIS test results show that the sample has a lower resistance value and less carrier transmission resistance.The special structure of the preferred orientation makes the photogenerated electron lifetime of the material longer and the transmission resistance smaller,which improves the photocatalytic nitrogen fixation performance of the catalyst.The presence of ammonia in the solution was determined by ion chromatography and the yield of ammonia was determined by Nessler colorimetric method.Variables controlled experiments show that photocatalytic nitrogen fixation activity is only present when light,catalyst and nitrogen are present simultaneously.On the basis of the microemulsion-solvothermal combination method,the bismuth tungstate system was further modified by molybdenum doping.The XRD patterns showed that as the amount of molybdenum doping increases,the bismuth tungstate will become more and more amorphous.The crystallinity of the metal bismuth also becomes stronger first and then becomes weaker as the amount of molybdenum doping further increases.SEM images show that the morphology of the sample after molybdenum doping is irregular spherical,and the degree of irregularity increases with the increase of doping amount.The XPS spectra show that the molybdenum element in the doped sample exists in the form of pentavalent,UV-Vis absorption spectra show that the absorption edge of the sample after doping is significantly broadened,and the maximum absorption wavelength is extended to the near-infrared region.The PL spectra show that the fluorescence intensity of the sample after molybdenum doping becomes lower,indicating the separation efficiency of photogenerated electrons and holes is higher.The TRPL spectra show that the photo-generated carrier lifetime of the doped sample is significantly higher than that doping before.The doped molybdenum can not only act as an active site for activating nitrogen,but also increase the maximum absorption wavelength of the material and prolong the lifetime of photogenerated carriers.Therefore,the photocatalytic nitrogen fixation activity of our material is enhanced.Variables controlled experiments have shown that photocatalytic nitrogen fixation activity is only present when light,catalyst and nitrogen are present simultaneously.