Volumetric hydrogen adsorption capacity of densified MIL-101 monoliths

The hydrogen adsorption isotherms of MIL-101 compressed pellets at 77.3 K are reported. The specific surface area and micropore volume decrease rather sharply when the pellet density approaches the crystal density. Optimum volumetric storage capacity of 40 g L⁻¹ is obtained for monoliths of remarkable mechanical integrity. The X-ray diffraction patterns do not exhibit notable changes with compression up to densities close to the crystal density. However, the infrared spectra show significant modification of the band structure in the range of vibration frequencies characteristic to the carboxylate and phenylene groups, due to the pressure-induced changes in the coordination environment of the metal, close to the adsorption sites. The compression effect on hydrogen adsorption can be correlated with the changes in the nitrogen adsorption isotherms. The results are discussed and compared with the literature results on volumetric hydrogen storage capacity of MOF-5 and MOF-177 monoliths.