Rational Synthesis And Adsorption/Separation Of Cage-based Metal-organic Frameworks

As more and more factories are builded,the emission of carbon dioxide has caused serious environmental pollution and social problems.Low-carbon hydrocarbons in industry are mainly produced by petroleum cracking.There are multiple component gases in the production process,which makes it difficult to obtain a single gas.Water pollution is also a serious problem,and especially hexavalent chromium Cr(VI)has caused serious harm to human health and the environment.Traditional separation methods have many disadvantages such as high energy consumption and large investment.So we need to find other efficient and inexpensive methods.Metal-Organic Frameworks materials have attracted much attention due to their excellent adsorption and separation properties.Compared with the conventional MOFs cage-based MOFs materials,as a special type of MOFs with ordered cavities and adjustable windows,can provide unique cage-like structures to trap small molecules.Based on these properties,Construction of ideal cage-based MOFs is of great importance.The idea of this thesis focuses on the synthesis of a series of cage-based MOFs with different structural characteristics through crystal engineering and supramolecular self-assembly strategies.Chemical property studies were conducted on the properties of some compounds.The cage-based MOFs were mainly tested for CO₂/N₂,C₂H₂/CO₂,C₂/C₃gas separation,for the application of dichromate(Cr₂O₇^2-)ion adsorption in solution and for stability in water or acid-base solutions.Seven cases of cage-based MOFs crystals were used for the study as follows:1.Two examples of anionic cage-based MOFs-compounds 1 and 2 were obtained using different kinds of metal salts mixed with triangular nitrogen-containing ligands.The SO₄^2-ligand in compound 1 is attached to the copper ion in tetrahedral form and further forms a super tetrahedral structural unit with the 2,4,6-tris(4-pyridyl)1,3,5-triazine ligand.Compound 1 has a(3,12)-linked TTT network topology,which is effective for CO₂/N₂separation.Compound 2 is an ionic fluorine cluster-based Si F₆^2-material with two F^-coordinated to copper ions in a junctional manner,and still four active F^-are exposed inside the framework.The presence of interpenetration inside the framework affects the gas adsorption.2.Two examples of macroporous cage-based MOFs materials,compounds 3 and 4,were by using triangular-shaped nitrogen-containing ligands with metal salts.Compound 3 is a MOF material with mononuclear copper as the growth node,and the three-dimensional supramolecular structure is constructed by?-?stacking and hydrogen bonding between layers.The internal pore is completely occupied by Zr F₆^2-and Zr₂F₆²⁺with the purpose of maintaining charge balance but not participating in coordination.Compound 4 was prepared by constructing octahedral cage basic unit by solvothermal method,and then preparing porous cage-based MOF by stacking octahedral cage.Compound 4 was applied as a physical adsorbent for the adsorption of Cr₂O₇^2-in aqueous solution,and the adsorption amount could reach 97.03%within 48 h.The crystalline form remained in a more intact state after adsorption.3.Three examples of isomeric super tetrahedral cage MOFs-compounds 5,6 and 7 were constructed using different metal salts mixed with two types of delta-type ligands.These cage-based MOFs are formed by the self-assembly of trinuclear metal ion cluster nodes(Co₃,Ni₃,Co₂Ti)with organic ligands through coordination bonds.They form a sodalite mesh topology in an angle-sharing manner,with?-cavities of mesoporous size(?22(?)).Compound 7 is not only thermally stable and resistant to acids and bases,but also has excellent properties for the separation of C₂H₂/CO₂.