Design And Preparation Of Metal-orgnic Frameworks For The Adsorption And Separation Of SF₆ And CH₄ Greenhouse Gases

As the main greenhouse gases,SF₆and CH₄always exist in the form of N₂mixture in practical applications.If they are emitted directly into the air after use without treatment,they will waste this valuable resource and cause significant environmental contamination,so adsorption and purification of the gas mixture is required to reduce emissions and improve resource utilisation.Metal-organic frameworks materials（MOFs）are new porous materials with large specific surface area,high porosity,tunable pore channels,and tunable chemical properties that show potential applications in gas separation.However,there is a general problem of relatively low adsorption capacity or separation selectivity to meet industrial requirements,so the development of efficient adsorbents is necessary.In this work a variety of MOFs are designed and synthesised and used for the separation of SF₆/N₂and CH₄/N₂mixtures.The main research work in this thesis is as follows:（1）An ultramicroporous nickel-based metal-organic framework material Ni（NDC）（TED）_0.5functionalized with multiple naphthalene rings was used for the separation of SF₆/N₂gas mixtures.This MOF exhibited unprecedented IAST-predicted SF₆/N₂selectivity（750）and low pressure SF₆adsorption capacity(61.86 cm³cm^-3).Theoretical calculations indicate that the center of the splint-like pores of the material is the optimal adsorption location.At the same time,the affinity between SF₆and the framework is strong due to the short interaction distance between the F atoms on SF₆and the pore wall.The penetration experiments further demonstrate that this MOF can completely separate the SF₆/N₂mixture,and the breakthrough absorption(56.60 cm³cm^-3)and cause-free time（τ:281.8）of this material for SF₆are 1.6 and 2.5 times higher than those of the currently reported benchmark material（Cu-MOF-NH₂）,respectively.At the same time,the material has good structural stability and recoverability,making it ideal for the recovery of SF₆from SF₆/N₂gas mixtures.（2）Two CH₄-selective MOFs,Ni（NDC）（TED）_0.5and Ni（ADC）（TED）_0.5,were synthesized by altering the carboxylic acid bond in Ni（BDC）（TED）_0.5,and their pore size and non-polar aromatic ring were precisely controlled.The experimental results show that Ni（ADC）（TED）_0.5has the most suitable pore size and low polarity,while it displays high CH₄/N₂separation selectivity（8.0）and CH₄adsorption capacity(31.2 cm³g^-1),especially its selectivity is higher than all conventional adsorbents（e.g.zeolite and carbon materials）,nickel-based MOFs and most other reported MOFs.Penetration experiments have shown that Ni（ADC）（TED）_0.5can completely separate CH₄/N₂mixtures.With this work,we demonstrate that in the context of CH₄/N₂separation,tuning the pore size and chemical properties by adding non-polar naphthalene or anthracene rings can enhance the interaction between the CH₄molecule and the framework.The design principles revealed in this work are general,which will provide some guidance for the design and implementation of some novel CH₄-selective materials with suitable pore size and non-polar chemical properties to improve CH₄/N₂separation performance.（3）The adsorption and separation performance of a stable metal-organic framework material（ZU-610）for methane and nitrogen mixtures in unconventional natural gas was systematically investigated.The material was synthesized using a hydrothermal method and experimentally prepared with good morphology,high crystallinity and purity,and excellent thermal stability.298 K,1 bar,ZU-610 exhibited CH₄and N₂adsorption capacities of 15.8 and3.0 cm3 g-1,and the CH₄adsorption capacity exhibited by this material has exceeded that of many materials reported so far,in addition to ZU-610exhibiting good CH₄/N₂selectivity（7.2）.To further explore the separation performance of ZU-610 for CH₄/N₂mixtures,the penetration experiment of ZU-610 was carried out at normal temperature and pressure.The experimental results showed that the material could completely separate CH₄/N₂mixture.The adsorption cycle experiment proved that the material had excellent regeneration performance.Therefore ZU-610 can separation of CH₄/N₂mixtures.