Synthesis And Photocatalytic Hydrogen Evolution Performance Of Mesoporous Graphitic Carbon Nitride-based Composites Photocatalysts

With the rapid development of human society,the contradiction between energy and environment has become increasingly serious.Fortunately,due to the advantages of environmental protection and sustainability,the photocatalytic technology provides the important theoretical basis research and practical application for the solution.Since photocatalytic technology was investigated,the key of developing photocatalysts is the exploration of suitable photocatalytic materials.Recently,various photocatalytic materials have been investigated.Among them,the graphitic carbon nitride has attracted widely attention from researchers due to its advantages of low price,convenient preparation,stability and high efficiency.With the suitable band gap structure,the graphitic carbon nitride can respond under the visible light irradiation,but the poor utilization of visible light seriously limits the improvement of photocatalytic performance due to it low specific surface area.In order to improve photocatalytic performance of graphitic carbon nitride,the mesoporous structure has been introduced to increase the specific surface area by morphology control.In this paper,mesoporous graphitic carbon nitride was selected as main research object,and its photocatalytic water splitting for hydrogen evolution has been investigated.Through the morphology modification of mesoporous graphitic carbon nitride and cocatalysts,the different cocatalysts（Metals（Pt,Ag,Ni）nanoparticles,PtS₂ nanosheet,Co-NG nanosheet）were prepared and coupled with mesoporous graphitic carbon nitride to obtained different complex photocatalysts.Besides,this paper revealed the reasons for the improvement in photocatalytic performance from the aspects of mesoporous structure,cocatalysts and transfer of photogenerated electrons.The research results are as following:（1）Through the multiple vacuum-induced methods,the metals nanoparticles had been induced into the mesoporous structure,and contacted closely with mesoporous channels to obtain the novel V-M（M=Pt,Ag,Ni）/MCN composites.By the series characteristics such as XRD,ICP,N₂ adsorption desorption experiments et al.,the morphology structure,element component and photocatalytic hydrogen evolution activity were investigated.The results indicated that the V-M（M=Pt,Ag,Ni）/MCN exhibited the higher photocatalytic H₂ evolution performance compared with P-M（M=Pt,Ag,Ni）/MCN due to the photogenerated electrons can concentrate within the mesoporous structure by vacuum-induced methods.（2）Through the liquid exploitation methods,the defects-enrich PtS₂ nanosheet had been prepared and coupled with mesoporous graphitic carbon nitride by electrostatic self-assembly to obtain the PtS₂/MCN composites.By the series characteristics such as XRD,AFM,XPS,Raman et al.,the morphology structure and element component were investigated.Through the photocatalytic H₂ evolution experiments and ESR,the photocatalytic performance and mechanism of photocatalytic reaction were investigated.The results indicated that the two-dimensional PtS₂ nanosheets can decrease the distance of electron transfer and promote the photocatalytic H₂ evolution performance.Among them,1wt%PtS₂（U）/MCN exhibited the optimal photocatalytic performance(¹168μmol·g^-1),and the apparent quantum efficiency（AQY）atλ=405nm was 1.16%.（3）Through one-step calcination strategy,the two-dimensional mesoporous graphitic carbon nitride had been prepared and coupled with the nitrogen-doped graphene that anchored Co atoms to obtain the novel 2D-2D Co-NG/TMCN composites.By the series characteristics such as SEM,TEM,AFM,XPS et al.,the morphology,structure and photocatalytic performance were investigated.Due to the formation of the fast electron transfer channels by 2D-2D structure,the Co-NG/TMCN composites exhibited the good photocatalytic performance.Among them,the 10wt%Co-NG/TMCN exhibited the optimal photocatalytic H₂ evolution activity(²947μmol·g^-1),and the apparent quantum efficiency（AQY）atλ=405 nm was 1.69%.