Synthesis Of Novel Porous Materials In Supercritical CO₂ And Their Applications

Metal organic frameworks(MOFs)and covalent organic framework(COFs)materials have been used in a wide range of applications due to their standout properties such as high porosity,large specific surface area and regular microporous channels.In this paper,metal organic framework ZIF-67 and covalent organic framework COF-LZU1 were synthesized in supercritical carbon dioxide.ZIF-67synthesized under the optimized conditions was applied to the adsorption of CO₂,and its adsorption performance was investigated.Using cobalt(?)acetylacetonate as the metal precursor and 2-methylimidazole as the organic ligand,ZIF-67 was synthesized in supercritical carbon dioxide without adding any organic solvents.The effects of reaction pressure,reactant ratio,reaction temperature,and reaction time on the synthesis of ZIF-67 have been investigated.Under the proper reaction conditions of 40°C and 20 MPa for 3 hours with the molar ratio of Co²⁺to 2-methylimidazole as 1:4,the synthesized ZIF-67 has rhombic dodecahedron morphology with both microporous structure and mesoporous structure and the specific surface area of 1182 m²·g^-1.Compared with traditional synthesis methods,the preparation of ZIF-67 in supercritical CO₂ has the advantages of time saving and no use of organic solvent,and the synthesized ZIF-67 has larger specific surface area and pore volume,which is beneficial to the application as adsorbents for CO₂ capture.ZIF-67 material synthesized under the proper conditions was used as CO₂adsorbents,and its adsorption behavior and performance were studied.It has been found that it has a good adsorption capacity for CO₂ due to its large specific surface area,pore volume,and hydrogen bonds in the framework.The maximum CO₂adsorption capacity was 1.37 mmol·g^-1 at 25 ?.The adsorption process conforms to the second-order adsorption kinetics curve.Moreover,as the CO₂ adsorbent,ZIF-67exhibited a good cycle stability with the adsorption capacity of 1.29 mmol·g^-1 after 5cycles.Using triformylbenzene and p-phenylenediamine as reactants,COF-LZU1 was synthesized in supercritical carbon dioxide with acetic acid as catalyst and DMF as co-solvent.The effects of co-solvent,reaction temperature,reaction pressure,acetic acid content,reaction time and reactant ratio on the crystal structure and micromorphology of COF-LZU1 have been investigated.The proper conditions are40 ? and 20 MPa for 6 h with the molar ratio of triformylbenzene to p-phenylenediamine to acetic acid as 1:1.5:15 and the volume ratio of DMF to acetic acid(3 M)as 1:1.The synthesized sample has the morphology of nanorods with good crystallinity,it also has excellent thermal stability which exceeds 550 ?.Compared with conventional synthesis methods,the preparation of COF-LZU1 in supercritical CO₂ has the advantages of time saving and usage of less organic solvent,and the synthesized COF-LZU1 has excellent thermal stability.