Research On Design,Preparation And Preformance Of Two-Dimensional Materials Based Photocatalysts

Environmental pollution and energy shortage have become two major problems hindering the rapid development of society.It is urgent to develop clean energy and efficient pollutant treatment technology.Photocatalysis based on semiconductor is a promising green technology for environmental purification and energy production.The technology works by creating pairs of electron holes when specific semiconductors are excited by sunlight,which are used to degrade pollutants and convert energy,among other things.The core of this technology is photocatalyst,so the design and development of catalyst with visible light response and good electron-hole pair separation efficiency becomes the key in this technology.Since entering the era of two-dimensional materials in 2004,such materials with many novel properties have become a research hotspot.Two-dimensional materials have large specific surface area,atomic thickness and more active sites,which are very suitable for the design and development of photocatalysts.The composite photocatalyst based on two-dimensional materials can further improve the catalytic activity,mainly due to the promotion of photocarrier separation.In this paper,a series of superior performance composite photocatalysts were designed and developed based on graphene,black phosphorus,Zn In₂S₄ and g-C₃N₄,respectively.The phase structure,morphology and optical absorption properties of composite photocatalysts were studied by various characterization methods and calculation analysis,and the photocatalytic degradation of pollutants and photocatalytic hydrogen evolution were applied.The details are as follows:（1）Synthesis and photocatalytic degradation of GO/α-Ag VO₃.A series of GO/α-Ag VO₃composite photocatalysts were synthesized by simple in situ coprecipitations at room temperature.Morphology and structure characterization show that the prepared Ag VO₃ is theαphase,which tends to grow along the c-axis perpendicular to plane（002）,and forms 2D/1D carbon based heterostructure after tightly coupling with the wrinkled GO nanosheets.The performance and stability of GO/α-Ag VO₃ samples were investigated by rhodamine B（Rh B）degradation test.The results show that GO/α-Ag VO₃ with 0.5wt%GO have the best photocatalytic degradation performance among all the samples.After irradiation with visible light for 40 min,the degradation efficiency of Rh B by 0.5wt%GO/α-Ag VO₃ is up to 90%,and the apparent reaction rate constant is 18 times higher than that of pureα-Ag VO₃,and it can maintain good stability.First-principles calculations and heterojunction analysis show that the increase in the catalytic activity of GO/α-Ag VO₃ nanorods is due to the appropriate band gap width and the formation of carbon based heterojunction.（2）Synthesis of BP/Zn In₂S₄ and study on photocatalytic hydrogen evolution.A series of new BP/Zn In₂S₄ photocatalysts were successfully synthesized by liquid phase ultrasound combined with solvothermal method.The morphology and structure of the composite photocatalyst were characterized.The results show that both the BP nanosheets and Zn In₂S₄ nanosheets are ultrathin two-dimensional materials,and the average thickness of BP nanosheets is about 3 nm.Zn In₂S₄ nanosheets are tightly attached to the larger BP nanosheets by face to face,forming a 2D/2D heterojunction with unique nanoscale.Under visible light irradiation,BP/Zn In₂S₄ heterojunction show better photocatalytic hydrogen evolution activity than BP or Zn In₂S₄ nanosheets.Among them,5wt.%BP/Zn In₂S₄ have the best photocatalytic hydrogen evolution activity,and the highest rate is 1317μmol h^-1g^-1,which is 3.35 times that of pure Zn In₂S₄ nanosheets(393μmol h^-1g^-1).The photocatalytic mechanism analysis results show that the Zn-P chemical bond between BP and Zn In₂S₄ nanosheets contributes to the photogenerated carrier migration efficiency.After the Z-scheme heterojunction is formed,it can also promote the separation of photogenerated charge in space,so the photocatalytic hydrogen evolution performance of composite samples can be greatly improved.（3）Synthesis of BPQDs/g-C₃N₄ and study on photocatalytic hydrogen evolution.BPQDs/g-C₃N₄composite photocatalyst was successfully synthesized by mixed ultrasonic agitation.Experimental characterization shows that BPQDs are uniformly loaded on g-C₃N₄ surface and formed 0D/2D heterojunction with broad spectral absorption capacity.Under visible light irradiation,BPQDs/g-C₃N₄ shows better photocatalytic activity of hydrogen evolution than bulk g-C₃N₄ and g-C₃N₄nanosheets.The photocatalytic rate of BPQDs/g-C₃N₄ is 678.1μmol h^-1g^-1.The enhanced activity of photocatalytic hydrogen evolution may be due to the formation of typeⅡheterojunction between BPQDs and g-C₃N₄,which promotes the separation of electron-hole pairs.