Design And Construction Of G-C₃N₄ And Metal Phosphide Photocatalyst With Enhanced Separation And Transportation Of Photogenerated Carriers For Efficient Hydrogen Production

Photocatalytic water splitting to produce hydrogen has potential and broad application prospects in energy and environmental fields,its core purpose is to design catalysts that are efficient,stable,green and inexpensive.However,most photocatalysts are limited by too narrow light adsorption range or too fast photocarrier recombination rate,so their photocatalytic activity and efficiency are not high.Therefore,in order to achieve better hydrogen evolution performance,this article is devoted to exploring and solving the problem of low separation efficiency of photogenerated carriers.Strengthen the separation and transfer of photogenerated electrons to promote the activity for photo-catalyst.Meanwhile,the mechanism of internal electronic transition and transfer was deeply investigate,which provide new methods for the design and construction of new types of photocatalysis,and a new ideas for optimizing the performance of photocatalytic hydrogen production.The main work contents are as follows:（1）The Ni-Cu bimetallic nanoparticles were successfully anchored on the surface of g-C₃N₄ nanosheets by a simple heat treatment process which was applied to the photocatalytic hydrogen evolution reaction.In-situ introduction of Ni-Cu could significantly improve the photocatalytic hydrogen evolution performance compared with pure g-C₃N₄ in the EY sensitization system under visible light irradiation.The excellent electrical conductivity of the bimetallic Ni-Cu and the close interfacial contact between Ni-Cu and g-C₃N₄ played an important role for improve the charge transfer rate.This are also the reasons why the charge separation efficiency is higher and the activity of photocataluytic hydrogen production is significantly enhanced.Ni-Cu/g-C₃N₄ coupling with a close schottky interface between metals and semiconductors which enhances H₂-evolution performance and the kinetics of TEOA oxidation.（2）The electronic structure and carrier behaviors of g-C₃N₄ are modified by a strategy of in-situ growth of Ni S-WO₃.The Ni S-assisted WO₃/g-C₃N₄ heterojunction system provides more active sites for the formation of heterojunction system which could promote charge separate and transfer efficiently.When photocatalysts are added to this system,Ni S,which is used as co-catalyst,can significantly increase the photocatalytic hydrogen production rate,reaching 2929.1μmol g^-1 h^-1 below the illumination.The improvement of photocatalytic performance can be owing to two aspects.First,the heterojunction formed by WO₃/g-C₃N₄ greatly improves the recombination for photogenerated carriers.Additionally,the exist of Ni S improves the electron mobility rate and provides more active sites for hydrogen evolution,which are proved with,a succession of studies like XRD,FT-IR,TEM,SEM,BET,UV-vis DRS,XPS,photoelectric performance test and steady state/transient fluorescence.This work provides a hopeful approach for improving the property of g-C₃N₄ from the perspective of electronic structure and carrier behavioral regulation.At the same time,it provides a new understanding for the construction of g-C₃N₄ heterojunction composite materials.（3）The Cu-MOFs@ZIF-9（Co）core-shell precursor was treated by low temperature phosphorization to obtain a Cu₃P@Co P composite catalyst with a self-supporting structure.The composite of Cu₃P@Co P not only possess a hierarchical structure,but built a p-n heterojunction at the interface.The unique structure and composition of Cu₃P@Co P could promote charge migration,provide large surface area and rich active sites to drive water photolysis.In addition,by controlling the degree of phosphating degree of Cu-MOFs@ZIF-9（Co）material and adjusting the ratio of Cu and Co,it was found that the maximum hydrogen producing activity of the composite photocatalyst reached 469.95μmol(9399μmol h^-1 g^-1),and it had a very excellent cycle stability.The results for photoelectrochemical and fluorescence tests showed that suitable conduction and valence band positions of Cu₃P and Co P formed a more effective path for the thermodynamic charge transfer.The construction of p-n type heterojunction provided a fast electron transfer channel in the Cu-P@Co-P interface.The special structrue and the existence of the bult-in electric filed in the p-n heterojunction made the photogenerated carriers in the composite have more effective separation and lower recombination rate,which significantly enhanced H₂ production activity.（4）The Mo-S@Mo-P heterojunction was successfully constructed on the surface of Mo-S nanospheres by simple phosphating.The introduction of phosphorus created a special electron transfer pathway on the surface of catalyst.Mo-S-P nanoflowers were a unique and special hetrojunction photocatalyst constituted of mixed anions.The synergistic effect between sulfur and phosphorus produced a photocatalyst that was more active than those based on pure sulfide or pure phosphide.The Mo-S-P-15 composite photocatalyst hydrogen evolution reached 551.8μmol in 5 h under visible light irradiation(11036.1μmol h^-1 g^-1).A series of tests had shown that the application of this partial phosphating strategy increased the reduction potential of the composite catalyst on the one hand,thereby enhancing the reduction ability of the composite catalyst.On the other,it formed a Mo-S@Mo-P heterojunction after partial phosphating,which could effectively improve the separation efficiency of photo-generated charges,prolong the lifetime of photo-generated charges,and improve the performance of photocatalytic hydrogen production.These findings provide new insights into the construction of highly oriented heterojunctions for anisotropic semiconductors and provide new strategies for adjusting the surface structure and carrier behavior of photocatalyst.