Metal-organic Frameworks for Hydrogen Storage: Theoretical Prospective

The adsorption of H-2 in dehydrated and hydrated Materials of Institute Lavoisier (MIL-101) was investigated theoretically. The effect of terminal water molecules on adsorption as one of the more vital MIL-n trivalent chromium-based porous carboxylates in metal-organic frameworks application in the renewable energy field was also theoretically studied. The MIL-101 structures were optimized for geometry and energy minimization was performed. The calculations were carried out using density functional theory approach with B3LYP functional and mixed basis set of Lanl2DZ and 6-31G(d, p) for Cr and light atoms (C, H, O, F), respectively, as implemented in the Gaussian 09 program package. The spin and atomic charges distribution on the Cr metal atoms, adsorbate, and water molecules are calculated using natural bond orbital (NBO). The density of states (DOS) for the clusters was obtained using Gaussian smearing of Kohn?Sham orbital energies. The natural bond orbital (NBO) for molecular orbital analysis and atomic charge calculations were utilized. For the dehydrated MIL-101, more adsorbate molecules were found near the exposed Cr2 sites than the fluorine saturated Cr1 sites. Furthermore, terminal water molecules in the hydrated MIL-101 made more interaction sites and enhanced adsorption.