Photocatalytic Properties Of G-C₃N₄-base Heterojunction Prepared By Template Method

In recent years,due to the rapid increase of energy demand and over-exploitation of the environment,energy shortage and environmental pollution have become increasingly serious problems.As an inexhaustible and clean energy,solar energy has the potential to replace traditional energy.In particular,the use of photocatalytic hydrogen production has been widely recognized in the energy and environmental protection field due to its low cost,non-polluting and efficient development of solar energy.Therefore,various types of photocatalytic materials are emerging one after another.Among them,g-C₃N₄ has easily synthesized method,suitable electronic band structure,visible light response ability,high physical and chemical stability and its“earth-abundant”nature,etc.have attracted the attention of researchers.However,the application of g-C₃N₄ in practice is severely limited due to its low conductivity,low specific surface area and high recombination rate of photogenerated carriers.Base on this,the photocatalytic performance of g-C₃N₄ was improved by increasing the specific surface area and reducing the recombination rate of photo-generated carriers.Generally,the g-C₃N₄ obtained by simple calcination is a bulk material of several micrometers or even several tens of micrometers,and the specific surface area is relatively small.Therefore,the porous structure of g-C₃N₄ is prepared by using SiO₂ nanospheres as a hard template to increase the specific surface area.In addition,this paper adopts the way of constructing heterojunction,which effectively promotes the diffusion and separation of photogenerated carriers,thus effectively reducing carrier recombination and improving photocatalytic hydrogen production efficiency.The content of this article has the following three aspects:?1?Porous g-C₃N₄ was prepared by using SiO₂ nanospheres as template.The porous g-C₃N₄ was dispersed in a mixture of Bi?NO₃?₃·5H₂O as bismuth source,KI as iodine source and ethylene glycol as solvent.Finally,the porous g-C₃N₄ modified by Bi₅O₇I nanoparticles was obtained by solvothermal method.The photocatalytic performance of Bi₅O₇I/g-C₃N₄ was 30times that of pure g-C₃N₄ by degrading phenol under visible light.The reason can be attributed to the heterostructure to effectively separate photogenerated carriers.?2?In recent years,black TiO₂ has attracted much attention due to its high photocatalytic performance.Therefore,in the second part,we introduct black TiO₂ into the template system.Specifically,using isopropanol as solvent,SiO₂ nanospheres as template,titanium tetraesopropoxide as titanium source,TiO₂/SiO₂ was obtained by stirring,centrifugation and calcination.Then,using the mixed solution of cyanamide and water,TiO₂/SiO₂ powder was dispersed by ultrasound,then during drying and calcining,and removing the template by NH₄HF₂ forming TiO₂/g-C₃N₄.Finally,the B-TiO₂/g-C₃N₄ was obtained by reduction of NaBH₄.It was detected by XRD,SEM,TEM and other instruments that g-C₃N₄ grew out of the hollow titanium dioxide nanosphere in the form of core-shell structure.The results of photocatalytic hydrogen production experiments show that the hydrogen production performance of B-TiO₂/g-C₃N₄ is 808.97?mol/g·h,which is about 65 times higher than unmodified g-C₃N₄,and about 18 times higher than TiO₂.It comes down to a highly efficient core-shell heterojunction,oxygen defects and a large specific surface area.?3?MoS₂ materials are widely concerned in the field of catalysis due to their high catalytic performance.Based on the B-TiO₂/g-C₃N₄ system,MoS₂ quantum dots were further deposited.The MoS₂ quantum dots were synthesized by one-step hydrothermal method using Na₂MoO₄ and L?+?-Cysteine?L-cysteine?as Mo source and S source respectively.Then,MoS₂ quantum dot solution was used as precursor liquid,and appropriate amount of B-TiO₂/g-C₃N₄ powder was added,fully stirred,reacted and dried to obtain B-TiO₂/g-C₃N₄/MoS₂ QDs composite product.The photocatalytic hydrogen production results show that the hydrogen production of B-TiO₂/g-C₃N₄/MoS₂ QDs is further increased to 1524.37?mol/g·h compared with the unmodified B-TiO₂/g-C₃N₄ system,which can be attributed to The unique energy band structure of MoS₂ quantum dots.