| Metal-Organic Framework (MOF) is a new type of porous materials constructed by metal clusters and organic building units through coordination bonds. These materials have shown significant potential for CO2 capture and separation due to their rich topology, high specific surface areas, tunable pore sizes and designable surface properties. However, it is difficult to find the balance between large storage capacity and high selectivity for CO2. In addition, hydrothermal stability is a serious problem to hinder its application. To obtain high-efficiency gases capture and storage /separation materials, the impact on gas adsorption in MOFs by various factors has also been explored.Based on the crystal engineering principles, it is recognized that M2(O2CR)4A2 paddlewheel-like unit are capable of generating square lattice (sql) or Kagome lattice (kgm) supramolecular isomers when dicarboxylates such as 1,3-benzenedicarboxylate (1,3-bdc) are exploited to link them. In this dissertation, we make efforts to generate 3D porous MOFs using containing carboxylate and nitrogen donor moieties via "pillaring" these layered MOFs. And we focus our attention on the merit of the functionalities for the materials CO2 uptake abilities. This dissertation mainly covers the following three parts:Firstly, SYSU, a porous MOFs has been successfully designed from Cu2(COO)4N2 paddlewheel-like unit, in which the vertices are linked into square lattice layers followed by being pillared via ligand-to-axis. Based upon the (3,6)-connected SYSU, iso-reticular NJU-Bai7 and NJU-Bai8 were designed by shifting the coordination sites of ligands to fine-tune pore size and polarizing the inner surface with uncoordinated nitrogen atoms, respectively, with almost no changes in surface area or porosity. Compared with SYSU, both the adsorption enthalpy and selectivity for CO2 of NJU-Bai7 and NJU-Bai8 have been greatly enhanced, which makes NJU-Bai7 and NJU-Bai8 good candidates for postcombustion CO2 capture. Notably, the CO2 adsorption enthalpy of NJU-Bai7 is the highest reported so far among the MOFs without any polarizing functional groups or open metalsites. Meanwhile, NJU-Bai8 exhibits high uptake of CO2 and good CO2/CH4 selectivity at high pressure, which arequite valuable characteristics in the purification of natural gases. According to data of the TGA and the temperature-variant PXRD, this type of sql-MOF shows good thermal stability. We also measured the stability in water and HC1 aqueous solution, they perform a peak shifting towards high degree without losing crystal lattice. These results make NJU-Bai7 and NJU-Bai8 good candidates for CO2 capture.Secondly, to further explore the CO2 storage capacities of this type of sql-MOF, we investigated the influence of metal ions in this type of MOFs. These MOFs have the same formula as NJU-Bai7 and NJU-Bai8 except for the metal ion and the static structures are slightly different due to narrowing channels. According to data of the TGA and the temperature-variant PXRD, this type of sql-MOF also shows good thermal stability. Unlike NJU-Bai8-Co, activating NJU-Bai7-Co, NJU-Bai7-Zn and NJU-Bai8-Zn by solvent-exchang strategy can not led to exhibit adsorption performance. Compared with NJU-Bai8, NJU-Bai8-Co exhibits a lower Brunauer-Emmett-Teller (BET) surface area, and equivalently high uptake of CO2 and slightly higher uptake of CH4. The different adsorptivities should stem from the slightly different stacking mode of the layers leading to the formation of meandering pores that induce effective groove sites.Thirdly, NJU-Bai15, NJU-Bai16 and NJU-Bai17 have the kgm layers being further pillared by the internal auxiliary nitrogen unit to form a three-dimensional microporous framework with alkyne/acylamide linking groups. They have micropores of the same "static aperture size" but different "effective aperture size". NJU-Bai15 and NJU-Bai16 exhibit high BET surface area of 1470 and 1134 m2·g-1 and total pore volume obtained from N2 isotherms is 0.563 and 0.451 cm3·g-1. Compared with NJU-Bai15, the adsorption enthalpy and selectivity for CO2 of NJU-Bai16 have been greatly enhanced due to the open Cu(Ⅱ) sites and the acylamide groups which act as strong interaction sites and play an important role in the high CO2 uptake of MOFs. The TGA and the temperature-variant PXRD data show this type of kgm-MOF has good thermal stability.To sum up, we use "apples with apples" comparisons to facilitate systematic study of binding affinity towards important guests such as small gas molecules (especially carbon dioxide). Fine-tuning pore size and insertion functional groups into the frameworks of MOFs may significantly enhance the CO2 adsorption behaviors; this observation may have significant implications for future design of new high-performance CO2 porous MOF materials. |
PDF Full Text Request