Preparation Of Metal Sulfides And Their Application In Photocatalytic Nitrogen Fixation

This article mainly focuses on the study and discussion of photocatalytic nitrogen fixation.Photocatalytic nitrogen fixation is a new photocatalytic technology with mild reaction conditions and no pollution.Photocatalytic nitrogen-fixing reaction is a process in which nitrogen is combined with protons provided by methanol（solvent）under the action of catalyst by solar energy to produce ammonia.In this process,the selection of catalyst,the solubility of nitrogen,the adsorption and activation of nitrogen on the surface of catalyst and the conditions of activity test all affect the performance of nitrogen reduction.In this article,the research background and basic principle of photocatalytic technology and photocatalytic nitrogen fixation,common ways of nitrogen fixation and the restrictive factors and solutions of photocatalytic nitrogen fixation are firstly described.In the exploration of photocatalyst that can improve the yield of photocatalytic synthesis of ammonia,the most common methods are the construction of defects in the sample structure,different morphology and the addition of co-catalyst for loading.In this article,the common metal sulfide is modified to study the performance of its photocatalytic nitrogen fixation.Secondly,defect structures of Zn₃In₂S₆ photocatalysts with different morphologies were carried out.Zn₃In₂S₆ with zinc vacancy was prepared from different sulfur sources,and the effects of the defects on the photocatalytic nitrogen fixation adsorption,activation and reaction were studied.The zinc vacancy in the Zn₃In₂S₆ nanosheet is electron-rich and can effectively activate the triple bond N≡N,thus improving the kinetic nitrogen reduction rate.When the N₂ molecule is activated at the zinc vacancy,the electron transfer rate between the N₂ molecule and the protons provided by methanol（solvent）will be greatly increased during the nitrogen reduction reaction.Zn₃In₂S₆ with rich zinc vacancy(355.2 mg/L/g_cat)showed higher activity than Zn₃In₂S₆ with lower zinc vacancy(23.3 mg/L/g_cat).Finally,we loaded the cocatalyst Mo S₂ on the common Cd S photocatalyst,aiming to study the change of the photocatalyst nitrogen fixation performance after the addition of the cocatalyst.By adjusting the load of Mo S₂,we found that when the mole ratio of Mo S₂/Cd S was 3%,the nitrogen fixation efficiency of the composite catalyst was the highest,which could reach 242.13 mg/L/g_cat.The addition of Mo S₂ causes the formation of heterojunction between Mo S₂ and Cd S.The special heterojunction structure can accelerate the separation speed of carrier and further improve the activity of photocatalytic nitrogen fixation.We also detected a large number of sulfur vacancies in the Mo S₂/Cd S composite catalyst through ESR test,which further proved the importance of defects in semiconductor materials for photocatalytic nitrogen fixation.This indicates that the structure of defects is conducive to improving the activity of photocatalytic nitrogen fixation,which provides a new solution for the future study of photocatalytic nitrogen fixation,and has important guiding significance for the photocatalytic nitrogen fixation system.