Investigation On The Preparation,Post-modification And Photocatalytic Performance Of Carbon Nitride And Zirconium-based Metal-organic Framework Materials

The development of industry and technology has guaranteed people’s daily life,but at the expense of the environment,improving energy and environmental issues is imminent.Energy and environmental issues have become major issues that we urgently need to solve at present!At the same time,photocatalytic technology emerged as a new type of clean and pollution-free technology,was widely used in photocatalytic water splitting,CO2 reduction,degradation of pollutants,and organic selective synthesis.etc.However,most of the photocatalytic reactions are not very efficient and still restricted by the narrow light absorption range and low quantum efficiency.Therefore,the development of new and efficient semiconductor photocatalytic materials is inevitable.Among a wide variety of photocatalytic semiconductor materials,graphite-like phase g-C₃N₄ and MOFs（metal-organic framework）materials have attracted widespread attention due to their excellent photocatalytic properties.g-C₃N₄ is stable,cheap,green,has a suitable energy band position and visible light absorption capacity,but low conductivity and severe photo-generated carrier recombination limit its further use.Therefore,it is necessary to further adjust g-C₃N₄ to enhance its photocatalytic performance.MOFs material is a porous material composed of metal sites,organic ligands and internal cavities.Unlike traditional photocatalytic semiconductor materials,it has a huge specific surface area and a rich porous structure,which gives it extremely strong adsorption capacity.Although the photocatalytic performance of MOFs is not ideal,its unique crystal structure can be easily modified to increase its surface active sites to obtain the corresponding photocatalytic performance.In this paper,based on the analysis of the reasons for the limited photocatalytic activity of g-C₃N₄,we promoted the separation of photogenerated electron-hole pairs by introducing the material with high hole mobility and constructing the heterojunction structures,thereby improving its photocatalytic performance.In order to expand the application of MOFs materials in photo-Fenton-like reactions,we adopt the method of post-modification of the organic ligands of MOFs materials,and use metal ions to modify the surface of UiO-66-NH2,thereby improving its corresponding catalytic activity.The main chapters of this thesis are as follows:In the first section of the first chapter,we gave a brief introduction to the current global energy and environmental issues,led to the importance of semiconductor photocatalysis in solving the above problems,analyzed the basic principles and research status of semiconductor photocatalysis,and focused on the application,constraints and solutions of photocatalytic CO2 reduction and photo-Fenton-like technology.In the second and third sections,we introduced carbon nitride and metal-organic framework materials,including their structure,properties,photocatalytic mechanism,advantages and disadvantages,and proposed corresponding solutions and design strategies for their shortcomings.Finally,the significance and subsjects of this thesis are drawn.In chapter two,by introducing the material with high hole mobility promotes the separation of g-C₃N₄ photogenerated carriers.The GDY@CNtb composite material was constructed through a simple self-assembly process by electrostatic adsorption andπ-π stacking between CNtb（g-C₃N₄ nanotubes）and GDY（graphyne）.By means of high conductivity and strong hole mobility of GDY,it can compensate for the poor conductivity and serious recombination of photo-generated carriers of g-C₃N₄.XPS spectroscopy revealed that there is a strong electronic interaction between GDY and CNtb,which provides evidence for the introduction of GDY to promote the separation of photo-generated carriers.The PL spectra and photocurrent response results also prove that the introduction of GDY suppresses the recombination of photogenerated carriers.Besides,the smaller resistivity radius of EIS further proves that GDY greatly enhances the conductivity of the material.Finally,the photocatalytic CO2 reduction performance test of the prepared samples proves that the catalyst can effectively convert CO2 into CO and CH4,and has excellent stability.In chapter 3,by constructing heterojunctions to promote the separation of g-C₃N₄ photogenerated carriers.The CNUN（g-C₃N₄/UiO-66-NH2）composite was prepared by in-situ hydrothermal growth method.Due to the special electron transfer method of the Type Ⅱ heterojunction structure,the separation efficiency of photogenerated carriers was significantly improved,and CNUN demonstrated a more efficient photocatalytic CO2 reduction ability than CN and UN.SEM and TEM images showed the close combination of CN and UN,which effectively promoted the electron transfer at the contact interface.DRS and valence band spectra provided evidence for the formation of heterojunction.In addition,the unique porous structure and the abundant amino functional groups on its surface of UN are conducive to the adsorption and activation of CO2,which jointly promote the photocatalytic reduction of CO2.In chapter 4,by modifying the organic ligand of UN（UiO-66-NH2）with Fe ions to improve its photo-Fenton-like ability.With the help of the complexation between amino functional groups and metal ions to form Fe-N bonds,Fe ions were successfully introduced into UiO-66-NH2.XRD,FT-IR,SEM and TEM（EDS）characterizations proved the successful preparation of the samples;in addition,the lone pair of electrons of the amino functional group can reduce Fe3+ to Fe2+,thereby achieving bivalent state loading.The introduction of light energy promotes the dynamic cycle of Fe3+ and Fu2+,and XPS characterization also confirms our point of view.The prepared catalyst was tested for photo-Fenton-like degradation of antibiotics,and it was found that under different reaction conditions（light source,H2O2 dosage,pH,temperature,catalyst dosage,etc.）,it had excellent degradation performance for different antibiotics.The active species capture experiment and EPR test verified that the reactive species was O2-,and the corresponding photo-Fenton-like mechanism was proposed.In chapter 5,we summarize the full text and put forward the main innovations and shortcomings,and look forward to the follow-up work.