Synthesis and Gas Storage Application of Porous Metal-Organic Frameworks and Nanomaterials

Abstract

PART I. Hydrogen Storage in Metal - Organic Framework Incorporating Crown Ether Moieties: Cation Inclusion A doubly interpenetrated metal-organic framework (MOF) incorporating a 18-crown-6 ether (18C6) moiety, Zn5(μ3-OH)2(TBADB-18-Cr-6)2•4DMF]•13DMF•4H2O (SNU-200), has been synthesized. SNU-200 not only provides binding sites with various cations (K+, NH4+, methyl viologen(MV2+), and Eu3+) but also exhibits characteristic gas sorption property depending on the bound cation. Despite the inclusion of the cations, SNU-200 retains the structure and the surface areas of MOF do not decreased. The MOF undergoes single-crystal to single crystal transformations upon cation binding together with the inclusion or coordination of the counter anion in the pores or at the metal site, respectively. To investigate the effect of the crown ether moiety and metal ions incorporated in the MOF on gas sorption properties, the adsorption-desorption isotherms were measured for N2, H2, CO2, and CH4 gases at various temperatures. SNU-200 shows a higher isosteric heat (Qst) of the H2 adsorption (7.70 kJmol-1) compared to other Zn based MOFs. Among the cation inclusions, K+ is the best for enhancing the Qst of the H2 adsorption (9.92 kJmol-1) as well as the adsorption selectivity of CO2/N2 (22.6).

PART II. Fabrication of Magnesium Nanocrystal in Highly Porous Materials for Hybrid Hydrogen Storage by Physi- and Chemisorption A 3D porous metal-organic frameworks, [Zn4O(atb)2]∙22DMF∙9H2O (SNU-90), have been prepared by the solvothermal syntheses from Zn(NO3)2 and aniline-2,4,6-tribenzoate (atb) ligand. SNU-90 is a non-interpenetrated (6,3)-connected net of a qom topology, similar to MOF-177 generating 3D channels. SNU-90 has Brunauer-Emmett-Teller (BET) and the Langmuir surface area of 4244 m2g-1 and 4914 m2g-1, respectively. Hexagonal-disk shaped magnesium nanocrystals of size 40 - 100 nm were embedded in a highly porous metal-organic framework, [Zn4O(atb)2] (SNU-90), where atb is aniline-2,4,6-tribenzoate, via chemical vapor deposition of Mg(cp)2 followed by thermal decomposition at 473 K under argon atmosphere. The shape and location of Mg nanocrystals were confirmed by HRTEM and tomography. Mg@MOF adsorbs hydrogen gas both by physi- and chemi- sorptions. The physisorption capacity at 77 K decreased as the amount of Mg embedded in MOF increased. However, the heat of H2 adsorption was increased from 4.55 kJmol-1 up to 11.6 kJmol-1 with increasing amount of Mg in the MOF. The hydrogen uptake capacity of the MOF at 298 K and 80 bar was also improved by the Mg nanocrystals from 0.45 wt% to 0.54 wt%. The Mg nanocrystals embedded in the MOF lowered the chemisorption temperature of hydrogen to 473 K, compared to 573 - 673 K for bare Mg powder of 50 - 100 µm. At 473 K and 30 bar, Mg@SNU-90 with a 10.5 wt% loaded amount of Mg chemisorbs hydrogen up to 0.71 wt%, which corresponds to 7.5 wt% of H2 adsorption in Mg alone. Highly porous covalent organic framework (Porous Aromatic Framework, PAF-1) has prepared by Ni catalyzed cross-coupling reaction of tetrakis (4-bromophenyl) methane. PAF-1 represents the diamondoid structure which consists of phenyl ring. It shows a high surface area (BET, 5640 m2g-1), exceptional thermal/ hydrothermal stability and the super hydrophobicity. The Mg nanocrystals (Mg NCs) were prepared in PAF-1 by reduction of Mg precursor that was vapor-deposited in the pore. The Mg of 11.87 wt% is included in PAF-1. The size of Mg NCs in PAF-1 is in a wide range from 17 to 400 nm, and it was characterized by HRTEM, and PXRD patterns. On exposure Mg NCs @PAF-1 to air for 10 days, the PXRD peak of Mg NCs still indicate a pure Mg peaks without any oxidation in nanosized Mg. In N2 and H2 gas sorption, as Mg incorporated in the PAF-1, surface area, pore volume, and H2 uptake capacity at 77 K and 1 atm decreased. However, the zero-coverage isosteric heats of the H2 adsorption is increased from 4.0 kJmol-1 to 5.8 kJmol-1.