The Preparation And Research Of Photocatalytic Nitrogen Fixation Of G-C₃N₄/BiOCl And W₁₈O₄₉/BiOCl Heterogeneous Materials

The photocatalytic ammonia production reaction can effectively utilize sufficient nitrogen in the air and alleviate global warming problems caused by traditional synthesis methods.The carriers generated on the catalyst surface promoted by light can activate the N-N bonds in the N₂ molecules,and combine with protons from water to convert into NH₃ molecules.BiOCl is considered as an attractive photocatalyst owing to its unique layered structure,non-toxicity,and stable chemical properties.However,the application in the field of nitrogen fixation is obstructed due to its low photogenerated carrier separation efficiency,large forbidden band width,weak light absorption and small specific surface area.In response to these problems,this paper modifies the BiOCl-based materials by adjusting the phase structure,surface morphology and constructing heterostructures.The main contents are as follows:1.The g-C₃N₄/BiOCl heterojunction composite material was synthesized by using normal temperature hydrolysis and high temperature polycondensation methods via controlling the experimental parameters such as the mass ratio of reactants,calcination temperature,calcination time and heating rate.Combining SEM,XRD,XPS,specific surface area test,ultraviolet-visible diffuse reflectance spectroscopy,photocurrent response and Mott-Schottky test methods to characterize the surface morphology,crystal structure and photoelectrochemical performance of the composite material.The results of the study indicate that the g-C₃N₄/BiOCl composite presents a two-dimensional sheet structure and good crystallinity under the optimized experimental conditions.The specific surface area is 33 times larger than that of pure BiOCl,which provides more active sites for the photocatalytic nitrogen fixation reaction.Meanwhile,the light absorption range of the g-C₃N₄/BiOCl material is extended to the visible light region,forming a“Z”semiconductor heterostructure,which promotes the effective separation of photogenerated electron-hole pairs and increases the nitrogen reduction activity.The photocatalytic ammonia production rate of g-C₃N₄/BiOCl reached 144.1μmol/g_cat/h,while the rates of pure g-C₃N₄ or BiOCl were 63.61 and 1.78μmol/g_cat/h,thus the nitrogen fixation efficiency was increased by 2.3 and 81 times respectively.2.In order to further enhance the photoelectrical response strength and conductivity of BiOCl-based materials,a one-step solvothermal method was used to prepare W₁₈O₄₉/BiOCl heterostructure photocatalyst.Optimizing the reaction solvent,reactant molar ratio,solvothermal temperature,solvothermal time and other experimental parameters to determine the best synthesis conditions.Combined with SEM,XRD,XPS,specific surface area measurement,electrochemical impedance,Mott-Schottky and other test methods,it diaplays that the W₁₈O₄₉/BiOCl composite performs a regular and orderly beam structure.The light absorption capacity in the ultraviolet and visible light range has been improved,and more photogenerated charges can be emerged.At the same time,the formation of“p-n”heterojunction is conducive to the separation and migration of photogenerated carriers,and the photocurrent intensity is three times higher than that of pure BiOCl.The ammonia production rate of W₁₈O₄₉/BiOCl heterogeneous composite photocatalyst.The ammonia yield of W₁₈O₄₉/BiOCl heterogeneous photocatalyst is 246.7μmol/g_cat/h,which is is increased by 138 times compared with pure BiOCl.