Synthesis And Characterization Of MOFs Based On A Sulfur-Containing Triazole-Carboxylic Acid Ligands

Metal-Organic Frameworks（MOFs）are a new form of porous coordination polymers.Because of their diverse structures,excellent porosity,ultra-high specific surface area,pore cage size suitable for gas absorption and good stability,MOFs can be used as adsorbents to achieve the function of storing energy gases,and they can also be selectively adsorbed through different interactions with the guest molecules to achieve effective separation and purification,so MOFs are ideal for theoretical studies and practical applications of gas adsorption.choice.In this study,a total of nine different metal-organic frameworks were constructed using sulfur-containing carboxylic acid-triazole organic ligands as linkers and different metal ions as nodes,followed by selection of representative MOFs for basic characterization tests and investigation of the CO2 adsorption separation performance of two 3D MOFs.This thesis consists of four chapters as follows.Chapter 1 is an introductory chapter,which introduces the concept,background,synthesis methods,classification of MOFs,applications in different fields and the research objectives and innovations of the selected topic.Chapter 2 of the work,the pioneering synthesis of triazole-carboxylic acid organic ligands containing thiophene moieties that have not been reported yet is presented.In this paper,sulfur-containing carboxylic acid-triazole organic ligands were used as linkers,and different kinds of metal salts were used as raw materials to screen the optimal synthesis conditions of metal-organic skeletal materials by varying the reaction temperature,reaction ratios,and solvent types.Nine novel MOF materials were successfully constructed under solvothermal conditions,which were tested and analyzed by single crystal diffractometer for two three-dimensional structures（compounds 1,compounds 2-4）,one one-dimensional structure（compounds 5-6）and one two-dimensional structure（compounds 7-9）,respectively.Their stability,basic composition,and coordination were subsequently determined by basic characterization using powder X-ray diffraction,thermogravimetry,carbon-hydrogen-nitrogen,and infrared.Among them,compound 2 was tested to be stable in water for 30 days and in strong acids and bases（PH=1,14）for 24 h without pore collapse,showing its excellent water stability and good acid and base resistance,which provides some experience and theoretical basis for the synthesis of new stable MOFs materials in the future.Chapter 3,since compounds 1 and 2 have a three-dimensional structure containing sulfur sites,as representative MOFs of the same configuration,they were tested separately for the adsorption and separation performance of gases to investigate the effect of S coordination sites on the CO₂ adsorption performance.Compound 1 has a large cubic pore and the S active site on the backbone was tested and studied to be able to coordinate Cu²⁺,so a certain amount of copper ions was modified into its backbone by post-synthesis method in this chapter.The adsorption test results showed that the adsorption of CO₂ was significantly enhanced for compound 1 modified with Cu²⁺,indicating that the open metal center is an active site for capturing CO₂ molecules.For compound 2 with one-dimensional pore channels,the pore size is small and the adsorption of copper ions is not obvious,so the gas adsorption test was performed directly,and it was found that it has excellent CO₂ adsorption capacity by itself.A mechanistic analysis was then performed and its performance for CO₂/N₂ selective adsorption was evaluated by IAST calculations.The work in this chapter provides new ideas for future research on S-containing MOFs in the field of CO₂ gas adsorption and separation.Chapter 4 focuses on the summary and outlook of the work in this thesis.