The solvent contained within the cylindrical one-dimensional pores of the novel three-dimensional metal organic framework Ni2(dhtp)(H2O)2.8H2O can be removed without decomposition of the network, allowing gas storage within the cavities.

No abstract

Hydrogen adsorption in two different metal–organic frameworks (MOFs), MOF‐5 and Cu‐BTC (BTC: benzene‐1,3,5‐tricarboxylate), with Zn2+ and Cu2+ as central metal ions, respectively, is investigated at temperatures ranging from 77 K to room temperature. The process responsible for hydrogen storage in these MOFs is pure physical adsorption with a heat of adsorption of approximately –4 kJ mol–1. With a saturation value of 5.1 wt.‐% for the hydrogen uptake at high pressures and 77 K, MOF‐5 shows the highest storage capacity ever reported for crystalline microporous materials. However, at low pressures Cu‐BTC shows a higher hydrogen uptake than MOF‐5, making Cu‐based MOFs more promising candidates for potential storage materials. Furthermore, the hydrogen uptake is correlated with the specific surface area for crystalline microporous materials, as shown for MOFs and zeolites.

Friction measurements were performed using gel samples equilibrated in distilled water against a glass substrate at room temperature, using a tribometer (Heidon 14S/14DR, Shindom Sci., Co.). The size of the gels was 20 mm 20 mm and they were 3 mm thick. The sample was embedded in a square frame of adjustable size and pressed against the glass surface that was fixed on the lower board. The glass surface was wetted with distilled water and was driven to move horizontally and repeatedly in a velocity range of 5 10 ±4 ±3 10 ±2 m s ±1 over a distance of 100 mm. Prior to the measurement, the glass plate was carefully washed with a cleaner, rinsed in distilled water, and dried in air. The measurements under various loads at a certain velocity were carried out using one sample, starting from the lower load and increasing the load continuously. The slidingvelocity dependence under a constant load was also measured in the same way. The detailed procedures are described elsewhere [10]. The frictional force per unit area (shear stress), f, and normal pressure, P, were calculated by dividing the frictional force, F, and load, W, by the surface area of the sample in the load-free state, respectively. The frictional coefficient, l, was calculated using the equation l = F/W.

The diameter is decisive: Adsorption sites for hydrogen in the metal–organic frameworks Cu‐BTC, MIL‐53, MOF‐5, and IRMOF‐8 could be identified by using thermal desorption spectroscopy at very low temperatures (see graph). The correlation between the desorption spectra and the pore structure of these MOFs shows that at high hydrogen concentrations the diameter of the cavity determines the heat of adsorption.