Preparation Of Metal-Organic Framework Decorated By Active Sites And Study On Adsorption And Separation Properties

The separation and purification of multi-component mixtures is an important direction of modern chemical industry.The design and synthesis of porous materials with pore structure and functional groups provide an opportunity for the development and popularization of new physical separation technologies with high efficiency and low energy consumption.Metal-organic frameworks（MOFs）have the advantages of adjustable structure and designable pore environment,which show good development trend and application prospect in the separation of small molecular hydrocarbons.In addition,the pollution control of volatile organic compounds（VOCs）is of great social demand and practical significance.MOFs materials have unique advantages in adsorption treatment of VOCs because of their large specific surface area and porosity.In the assembly process of MOFs,the choice of metal nodes and the type,symmetry,size,and functional groups of organic ligands play a decisive role in the formation of the final structures of MOFs and their possible applications.Among the common ligands for the construction of MOFs,nitrogen-oxygen donor ligands usually have the dual advantages of carboxylic acid ligands and azole ligands,while biomass ligands are biocompatible,environmentally friendly and easy to recycle.Based on the above research ideas,four porous MOFs materials with rich pore chemical environment and novel structures were constructed by using transition/rare earth metal ions with biomass ligands and highly symmetrical benzene carboxylic acid ligands substituted by pyridine,triazole and tetrazole,respectively.The crystal structure,gas/vapor molecular adsorption and separation properties were studied detailedly.The main research content of this paper mainly includes the following five chapters:Chapter 1:The concept,composition,and research progress of MOFs in the field of adsorption and separation of small molecular hydrocarbon gases and VOCs were introduced,putting forward the ideas of research and also presenting the research progress of this dissertation.Chapter 2:A mixed ligand strategy was used to construct a porous MOF with a yfy network structure,[Me₂NH₂][Zn3（ALP）（TDC）2.5]·3.5DMF·2H2O（1）using 2,5-thiophene dicarboxylic acid（H₂TDC）,biomass ligand allopurinol（ALP）and zinc acetate hexahydrate.The most obvious feature of complex 1 is the formation of three types of cages,and the pores in 1 are modified by the aromatic ring of the ligand,the abundant uncoordinated carbonyl O atom in ALP,the thiophene S atom and the carboxyl O atom.Therefore,the complex showed moderate acetylene and carbon dioxide capture capacity(the capture capacity of acetylene and carbon dioxide are 96.6 and 74.5 cm³ g^-1,respectively)and the selectivity of C₂H₂/CH₄（33.7）,C₂H_2/CO₂（3.0）.Furthermore,the separation ability of 1 for equal molar C₂H₂/CH₄,C₂H₂/CO₂ binary mixtures was verified by dynamic breakthrough experiments.Chapter 3:A bipyridine-substituted isophthalic acid ligand,4-bis（pyridine-4-yl）isophthalic acid（H₂dpip）,was designed and reacted with nickel sulfate hexahydrate under solvothermal conditions to construct a porous MOF,[Ni（dpip）]2.5DMF·H₂O（2）,with open tubular channels.The MOF has a sqc topology with 4,4 connections and contains two one-dimensional open channels with different pore size environments.The smaller channels are modified by carboxylic acid O atoms and have good adsorption capacity for acetylene,ethylene and carbon dioxide.At 298 K,the separation selectivities of complex 2 to C₂H₂/CH₄,C₂H₂/CO₂,C₂H₄/CH₄,CO₂/CH₄ was calculated by IAST,the corresponding selectivities values are 16.6,2,6.2 and 7.5,respectively.The dynamic breakthrough experiment further verified the separation ability of complex 2 to real mixed gas.In addition,2 also showed the selective adsorption capacity for alcohol（C1-C4 alcohols）and aromatic（benzene,cyclohexane and toluene）VOCs.Chapter 4:In order to further improve the gas separation ability of the prepared MOF materials,based on the research results in chapter 3,a triazole-substituted isophthalic acid ligand,4-bis（triazole-1-yl）isophthalic acid,was used to prepare a porous MOF[Co（btzip）（H₂btzip）]₂DMF·2H₂O（3）with fsc topology under solvothermal conditions.The pores in the MOF are modified by Lewis acidic carboxylic acid groups and Lewis basic uncoordinated nitrogen atoms,which can be used as C₂ hydrocarbons and CO₂ adsorption sites.The single-component adsorption isotherm shows that,compared with the complex 2with less active sites,3 has higher adsorption capacity for CO₂ and C₂ hydrocarbons and excellent selective separation ability for CH₄（C₂H₂/CH₄:24.4,C₂H₂/CO₂:2.5,C₂H₆/CH₄:16.3 and C2H4/CH4:24.8）.The dynamic breakthrough experiment results also further verify the excellent separation ability of 3 for C₂H_n/CH₄,C₂H₂/CO₂ mixed gas.In addition,3 shows good adsorption and separation ability for alcohol molecules（methanol,ethanol and 2-propanol）(the adsorption capacity is 88.0,64.7 and 36.6 cm³ g^-1,respectively,and the selectivity of methanol/1-propanol,methanol/2-propanol and 2-propanol/1-propanol is 8.1,2.5and 10.4,respectively).Chapter 5:Using F-functionalized carboxylic acid-tetrazolium ligand,2-fluoro-4-（1H-5-tetrazolyl-）benzoic acid（F-H₂tzba）,and dysprosium nitrate hexahydrate prepared a cage-like MOF,{[（CH₃）₂NH₂]₂[Dy₆（μ₃-OH）₈（FTZB）₆（H₂O）₆]·（solvent）}_n（4）based on Dy₆（μ₃-OH）₈（COO）₆（N₄C）₆ clusters.The free F atoms and uncoordinated tetrazolyl N atoms in the MOF not only show high acetylene,ethylene and aromatic VOCs adsorption capacity(adsorption capacities are 140.4,114.3 and 109.5 cm³ g^-1,respectively),but also reveal excellent C₂H₂/CH₄,C₂H₄/CH₄,C₂H₂/C₂H₄（selectivity is 15.7,14.9,1.1,7.8 and 2.8respectively）,benzene/toluene,benzene/cyclohexane separation selectivity.The dynamic breakthrough experiment further confirmed the feasibility of using 4 to remove C₂H₂ from the mixture of C₂H₂and C₂H₄ and to purify C₂H₂ and C₂H₄ from CH₄.