| Abstract |
This thesis investigates the synthesis and study of Metal-organic Frameworks (MOFs), for applications in gas adsorption, predominantly CO2, CH4, N2 and Η2.
The greenhouse effect and the subsequent depletion of natural fossil fuel, leads the research around the world towards “green applications”. Basic goal is the sequencing of CO2 emissions, which is the major contributor to the greenhouse effect. Methane has been suggested as a first line alternative for fossil fuel, due to its low C content leading to fewer CO2 emissions. Another alternative is the use of Η2 as fuel since the only byproduct during its burning is water. Both applications are economically and energetically costly. In the meantime, growing economies, like China and India, demand even more energy for their industry. As a solution to this, the use of MOFs as gas carriers has been suggested, mostly due to their high surface areas and their ability to be modified with tailor-made functionalities, depending on the application they are targeted for.
In the first part, the synthesis of a series of materials with ZnZr2+ SBUs bridged with bitopic (UoC-1a and UoC-1b) or mixed bitopic and tritopic ligands (UoC-2a and UoC-2b). UoC-1a and UoC-1b are isostructural to IRMOF-9 and is made up of the well known Zn4O SBU of IRMOFs bridged with –ΟΗ functionalized ligands. They show an increase in the uptake of the gases we are interested for and interact better in comparison to IRMOF-9, although they have a much smaller BET surface. UoC-2a and UoC-2b have a similar structure to MOF-205. H2ndc and H2ndc-oh are used in place of the ditopic ligand where as H3tatab is used instead of H3btb. UoC-2b is one of the few instances, if not the only, that the ligands of a MOF carry acidic and basic functionalities simultaneously. Gas adsorption for UoC-2a is described.
The second part investigates the synthesis and study of a series of Zr and Hf-MOFs, isoreticular to UiO-67, which have different functionalities on the bitopic H2bpdc ligand. The ability of these materials to have defects in their lattice in the form of coordinated AcO- or OH- on the Zr6(μ3-Ο)4(μ3-ΟΗ)4(-CO2)12 SBU, is proven via NMR and TG. These defects stem from the use of auxiliary (AcOH) or mineral acids (HCl) as co-reagents, which are necessary for the MOF synthesis. The presence of functionalities on the ligand causes significant improvement in the gas sorption properties, mostly CO2. UoC-3, functionalized with –SO2 groups leads to 122% increase in CO2 uptake and 55% increase in Qost compared to non functionalized UiO-67. Respectively UoC-7, functionalized with –NO2 groups, adsorbs 116% more CO2 and has 32% higher Qost compared to the starting MOF. The CH4, N2 and H2 uptake is described along with CO2/CH4 and CO2/N2 selectivity, in some of them.
The third part involves the synthesis of MOFs with AlZr3+ SBUs and the H2bpydc ligand. Coordination of PdCl2 and subsequent reduction using H2 at elevated temperatures, afforded MOFs loaded with metallic Pd nanoparticles. Materials with three different loadings were synthesized and characterized. The morphology and the specific surface area of the materials is described. These materials show enhanced H2 uptake at room temperature, which is assigned to the spillover effect.
In the fourth and last part of this thesis, the synthesis of two new materials with Zr4+ SBUs and quadratopic ligands with tetrahedral geometry, are described. The first one, UoC-12, has an ith topology and its gas sorption properties were studied, which are relatively high compared to other non functionalized Zr-MOFs. UoC-13 has a flu topology and the same ligand decorated with –SO2 and –SO2H groups is being used. The morphology and structure of this material is described.
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Νέα νανοπορώδη στερεά ανόργανου-οργανικού σκελετού για αποθήκευση και διαχωρισμό αερίων συμπεριλαμβανομένων H2, CO2 και CH4
