Construction Of Metal/Covalent Organic Framework And Adsorption Separation Of Acetylene And Carbon Dioxide

Acetylene（C₂H₂）is an important raw material widely used in the production of chemical products.In industry,trace carbon dioxide（CO₂）is inevitably mixed in the process of producing C₂H₂ through partial combustion of methane or steam cracking,which seriously affects the purity of C₂H₂ and its further applications,but since they have identical kinetic diameters and similar boiling points,the C₂H₂-CO₂ separation is extremely challenging.In recent years,crystalline porous material（CPM）shows its unique superiority and great application prospect in the field of separation of multi-component low-carbon hydrocarbon mixtures due to its visual crystal structure,regular channel structure and high porosity.Metal–organic framework（MOF）based on organic and inorganic components and covalent organic framework（COF）connected by light elements（such as C,H,O,N,B,etc.）has the advantages of high specific surface area,designable,easily functionalized and modified pore environment,which has become a new material in crystalline porous materials.The development of functional MOFs and COFs and the establishment of the relationship between structure and properties has become a research hotspot in many fields.Based on pyridine carboxylic acid and pyridine boric acid organic linkers,two cases of microporous MOF and one case of delicate COF materials were prepared,and their crystal structures and adsorption and separation properties of C₂H₂ and CO₂ mixtures were mainly studied.The main contents of the full text are as follows:In Chapter 1,reticular chemistry is summarized,and the structure of MOF and COF and their research status on adsorption and separation of C₂H₂ are reviewed,and the research idea and progress of this paper are proposed.In Chapter 2,the organic linker 2-（2-carboxypyridin-4-yl）terephthalic acid（H₃CPTA）was designed by introducing a chelating site that can form a five-membered ring and a stable MOF,Zn-CPTA,was assembled.Zn-CPTA is a 3D framework constructed from three Zn–O–Zn chain coordination CPTA^3–known as rod secondary building units.Its 1D pore is modified by uncoordinated carboxyl O atoms and exhibits excellent chemical stability in aqueous solutions with p H values ranging from 2 to 12.In gas adsorption studies,the microporous Zn-CPTA exhibited a high adsorption enthalpy of C₂H₂(50.6 k J mol^–1)and a moderate separation ratio of C₂H₂/CO₂.Continuous dynamic breakthrough experiments show that Zn-CPTA can completely separate the C₂H₂/CO₂ mixture.In Chapter 3,a flexible MOF,Zn-DPNA with the gate-opening effect was synthesized by regulating the binding site of the linker and using the isomer 5-（2’,5’-dicarboxylphenyl）nicotinic acid of H₃DPNA.The framework shrank after the removal of solvents.The transition from the large pore phase to the narrow pore phase is manifested as the dispersive 0D cage with narrow channels becomes a curved and interlaced cage.The adsorption isotherm of activated Zn-DPNA for C₂H₂ is a stepped isotherm,while the adsorption isotherm of CO₂ is a classical I-type isotherm.Due to the large adsorption difference before the gate pressure,Zn-DPNA has a good CO₂/C₂H₂ inverse separation ability at 298 K and low pressure.The molecular simulation showed that the high adsorption enthalpy of CO₂(43.1 k J mol^–1)was due to the strong electrostatic interaction between CO₂ and dimethylamine cation,which not only locked the hydrogen bond network formed by dimethylamine and the framework but also kept the framework in the narrow pore phase.The adsorption density and electrostatic potential indicate that the middle part of the cage in the large pore attracts C₂H₂ and repels CO₂,leading to the expansion of the narrow pore and further diffusion of C₂H₂.The structure of crystalline organic frames using dative B←N bonds（BNOF）has attracted more and more attention,but the lack of permanent porosity is an obstacle that must be overcome to ensure its application as porous materials.In Chapter 4,in order to control the final structure and reduce the possible by-products,the elegant 2D supramolecular BNOF-1 was synthesized in one step using the cheap and readily available bi-functional 4-pyridine boric acid,and make the structural prediction.4-connected boroxine rings act as nodes to bridge four trans-conformation pyridine and one coplanar pyridine to form a single-layer structure.2D networks generate a highly porous supramolecular framework through parallel stacking.BNOF-1 can be prepared on a large scale and can be dissolved and regenerated in organic solvents.It is worth mentioning that the framework not only has the highest BET surface area(1345 m² g^-1)of all BNOF materials to date,but also has the highest C₂H₂ and CO₂ adsorption capacity of all COF materials.In addition,breakthrough experiments also confirmed that BNOF-1 can effectively separate C₂H₂ from the C₂H₂/CO₂ mixture.