(28f) Experimental And Theoretical Studies Of Gas Adsorption In Cu3(Btc)2

Metal-organic frameworks (MOFs) are interesting materials for studying gas adsorption because they can be made in high purity, are highly crystalline, and have a very narrow range of pore sizes with virtually all of their pore volume falling within the IUPAC microporous regime. CuBTC [Cu₃(BTC)₂, where BTC=1,3,5- benzenetricarboxylate] (also known as HKUST-1) has garnered a good deal of attention since it was first reported by Chui et al.[1] We have improved the activation process for CuBTC by extracting the DMF solvated crystals with methanol; we identify material activated in this way as CuBTC-MeOH. This improvement allowed the activation to be performed at a much lower temperature, thus greatly mitigating the danger of reducing the copper ions. A review of the literature for H₂ adsorption in CuBTC shows that the preparation and activation process has a significant impact on the adsorption capacity, surface area, and pore volume. CuBTC-MeOH exhibits a larger pore volume and H₂ adsorption amount than any previously reported results for CuBTC. We have performed atomically-detailed modeling to complement experimentally measured isotherms. Quantum effects for hydrogen adsorption in CuBTC were found to be important at 77 K. Simulations that include quantum effects are in good agreement with the experimentally measured capacity for H₂ at 77 K and high pressure. We have studied the effects of framework partial charges on H₂ adsorption isotherms. Inclusion of charge-quadrupole interactions improves the agreement between the simulations and experiments at low pressures. We have compared the adsorption isotherms from simulations with experiments for H₂ adsorption at 77, 87, 175, and 298 K, nitrogen adsorption at 253 and 298 K, and argon adsorption at 298 and 356 K. Reasonable agreement was obtained in all cases. We have calculated the self and transport diffusivities of several different gases in CuBTC. The computed diffusivities are similar to those observed for gases in silicalite.

[1] Chui, S.S.Y.; Lo, S.M.F.; Charmant, J.P.H.; Orpen, A.G.; Williams, I.D. Science 1999, 283, 1148.