Synthesis, characterization and hydrogen adsorption properties of metal-organic framework Al-TCBPB

In this work, a new metal organic framework (MOF) was synthesized by using a large organic ligand 1,3,5-tris[4'-carboxy(1,1'-biphenyl)-4-yl] benzene (abbreviated as TCBPB) and aluminum as the metal that forms the secondary building unit (SBU) by solvothermal method. The MOF, named as Al-TCBPB, was characterized with pore textural properties, powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and FT-IR spectroscopy. Hydrogen adsorption was measured volumetrically at ambient pressure and temperatures of 77, 88 and 298 K and at high pressure (up to 9 MPa) for temperatures 77 and 298 K. Pore textural properties revealed a high BET surface area of 2311 m(2)/g, narrow bimodal pore widths of 11.8 angstrom and 20 angstrom and a total pore volume of 0.80 cm(3)/g. PXRD identified the crystal structure as monoclinic with space group c2/m. This MOF adsorbs 1.53 and 0.83 wt.% of hydrogen at 77 and 88 K, respectively, and pressures up to ambient conditions. At higher pressure of 9 MPa, it demonstrated an excess adsorption of 4.8 and 1.4 wt.% at 77 and 298 K, respectively; these high-pressure data fit well with modified Dubinin-Astakov (D-A) analytical model. The heat of adsorption values of Al-TCBPB vary between 5.9 and 4.9 kJ/mol for the hydrogen adsorption loading of 0.1-0.8 wt.% and decreases monotonically to approximately 2 kJ/mol when the adsorption loading becomes 4.8 wt%. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.