Photocatalytic Hydrogen Production And Nitrogen Fixation Performance Of Visible-light-response ZnIn₂S₄ And G-C₃N₄

Photocatalysis is considered to be an ideal way to solve the current energy problems.Photocatalysis can achieve solar hydrogen production and nitrogen fixation.Among them,hydrogen is a clean fuel and NH₃is the raw material for the production of fertilizers.Compared with wide band gap semiconductor materials（Ti O₂,Zn O,etc.）,visible light catalysts can make better use of sunlight.Among many visible light-responsive semiconductors,Zn In₂S₄has strong light trapping and hydrogen production activity,but the lack of active sites and photo-generated carrier recombination restrict the improvement of its photocatalytic hydrogen production efficiency.g-C₃N₄gas has a large adsorption capacity and is a good photocatalytic nitrogen fixation material,but its photocatalytic nitrogen fixation performance is not ideal because of its few photocatalytic active sites and serious carrier recombination.Therefore,in this paper,Zn In₂S₄ microspheres were synthesized to improve the photocatalytic hydrogen production performance by forming a large number of S vacancies,and the mechanism was studied;g-C₃N₄nanosheets were synthesized and loaded with Zn Fe₂O₄nanoparticles in order to enhance its photocatalytic nitrogen fixation performance,reveal the nitrogen fixation reaction mechanism.The specific research content is as follows:（1）Zn In₂S₄microspheres were synthesized by hydrothermal method,and the S vacancies obtained by plasma and annealing treatment were compared.The research results show that the sample obtained by plasma treatment has a better photocatalytic hydrogen production rate(720μmolg^-1h^-1),which is 1.2 times that of the sample obtained by annealing treatment and 5 times that of the untreated sample.The reason is that the S vacancies obtained by annealing treatment are uniformly distributed in the bulk and inside of Zn In₂S₄,while the sulfur vacancies obtained by plasma treatment are mainly concentrated on the surface of Zn In₂S₄.Density functional theory（DFT）calculation results confirm this point.The S vacancies formed on the surface of the ZIS will generate localized energy levels that can capture photo-generated electrons,thereby accelerating the light hydrogen production reaction process.The DFT calculation results also show that the S atoms near the S vacancies can be used as active sites for photocatalytic hydrogen production.experiment（2）The g-C₃N₄nanosheets are synthesized by the thermal polymerization urea method,and Zn Fe₂O₄nanoparticles are loaded on the surface to enhance its light nitrogen fixation performance.The research results show that the visible light nitrogen fixation yield of pure g-C₃N₄ is（4.4 mg/g/h）.As the content of g-C₃N₄ increases,the performance of light nitrogen fixation first increases and then decreases.When the content of g-C₃N₄ is 160 mg,the NH₄⁺output reaches the maximum value（25.3 mg/g/h）,which is about 6 of that of pure g-C₃N₄.Times.Under near-infrared light（>700nm）,it still has the performance of photocatalytic nitrogen fixation（5 mg/g/h）.The research results show that the reason for the performance improvement,which comes from the absorbance of the sample was significantly increased after the composite,and Fe doped into the g-C₃N₄ structure to form an Fe-N bond.DFT calculation results also confirm this,theoretical calculations prove that the g-C₃N₄ band gap formed after Fe doping forms a localized energy level,which can be used as a photo-generated carrier trap to inhibit the recombination of photo-generated carriers.In addition,Fe doping can increase the N₂ bond length and activate N₂ molecules.Density functional theory calculations show that Fe doping sites can be used as photocatalytic nitrogen fixation reaction sites.Therefore,the improvement of the sample performance after recombination is due to the increase of active sites caused by Fe doping,and the synergistic effect of heterojunction and local energy level enables the effective separation of photogenerated carriers.There are 30 figures,7 tables and 84 references in this thesis.