Study On Construction And Photocatalytic Activity Of Three-Dimensional Macroprous Graphitic Carbon Nitride

As a potential technology for new clean energy,photocatalytic technology has attracted much attention in recent years.The photocatalysts play a key role in during the conversion process of solar energy.Therefore,the search for photocatalysts with high activity,high stability and unexpansive is a hotpot of current researches on photocatalytic technology.Metal-free graphitic carbon nitride(g-C3N4)is gaining popularity by many researchers due to its high physicochemical stability,visible light absorption,and suitable band structure.However,g-C3N4 has some disadvantages,such as,low specific surface area,insufficient absorption of visible light,and easy recombination of electrons and holes,which all limit the applications in the field of photocatalysis.Thus,it is necessary to improve the photocatalytic activity through a suitable modification.In addition,three-dimensional macroporous(3DM)catalysts with good transport and diffusion properties exhibit excellent catalytic activity.In this thesis,the three-dimensional macropore g-C3N4 is mainly constructed by the template method and its surface structure is modified to increase the surface-active sites and reduce the photogenerated carrier recombination rate.Moreover,heterogeneous structures are constructed by combining with semiconductor materials to expand the visible light absorption range and enhance the photocatalytic activity through the synergistic effect of the interface.First,we synthesized three-dimensional macropore carbon-vacancy carbon nitride(3 DM C/g-C3N4)by a facile one-step calcining with polymethyl methacrylate(PMMA)spheres template.The method effectively constructed g-C3N4 macropore structure,which effectively improves the light utilization efficiency of g-C3N4 and significantly increases the surface-active sites.The introduction of a large number of surface carbon vacancies effectively expands the visible light absorption range and suppresses the recombination of photogenerated carriers.Compared with the unmodified bulk g-C3N4,the photocatalytic H2 evolution rate and photoreduction of CO2 to methanol rate of 3 DM C/g-C3N4 are significantly improved.The experimental results show that the construction of 3D macropore is an effective method to enhance the photocatalytic activity of g-C3N4.In order to improve the stability of the template sphere in the preparation process,we selected more stable silicon oxide ordered spheres as the template to prepared a three-dimensional ordered macroporous carbon nitride(3DOM g-C3N4)structure.The three-dimensional ordered and interconnected macroporous structure was synthesized by adjusting the experimental conditions,which can effectively promote the catalytic reaction,greatly shorten the migration distance of photogenerated carriers,reduce the recombination rate of photogenerated electrons and holes in the bulk,and elevate the photochemical reaction potential.Compared with the bulk g-C3N4,the construction of 3DOM g-C3N4 widens the bandgap and increases the specific surface area.An excellent photocatalytic H2 evolution performance was obtained by the 3DOM g-C3N4.Finally,the absorption range of visible light is one of the significant limiting factors for improving photocatalytic efficiency.The wide absorption band of visible light is closely related to the photocatalytic activity of g-C3N4.In order to achieve efficient H2 evolution of g-C3N4 under visible light,we combined 3DOM g-C3N4 and cadmium sulfide nanoparticles to construct heterogeneous structures(3DOM g-C3N4/CdS)by a photo-deposition method.The DOM g-C3N4/CdS heterostructure exhibited considerably improved photocatalytic H2 evolution activity under visible light.The prolonged lifetimes of photogenerated carriers and the synergistic effect are considered as key factors of the enhanced photocatalytic performance.