Zirconium-Based Metal-Organic UiO-66, UiO-66-NDC and MOF-801 Frameworks. Influence of the Linker Effect on the Hydrogen Sorption Efficiency

Metal-organic UiO-66, UiO-66-NDC, and MOF-801 frameworks (MOFs) are produced via the solvothermal synthesis technique. The frameworks are composed of Zr6O4(OH)(4) clusters that are connected with appropriate linkers, as follows: UiO-66-terephthalic acid; UiO-66-NDC-1,4-naphthalenedicarboxilic acid; and MOF-801-fumaric acid. The single-phase composition of the samples is confirmed by X-ray powder diffraction. The identification of Zr6O4(OH)(4) clusters in all the synthesized MOFs is established using X-ray adsorption spectroscopy. The specific surface areas of UiO-66, UiO-66-NDC, and MOF-801 are evaluated, and their hydrogen adsorption-desorption isotherms are measured at 77 K, as well. Comprehensive preliminary characterization of the samples, together with hydrogen-storage-capacity data, allows one to make the following conclusions: (i) at relatively high pressures, the highest hydrogen-storage capacity is found for UiO-66 with the largest specific surface area; (ii) at relatively low pressures, MOF-801 with the smallest pores possesses the optimal structure for hydrogen sorption; (iii) a large pi-system of aromatic UiO-66-NDC rings yields effective hydrogen sorption at low pressures, which is retained in pores during desorption.