| Abstract
| - This study combines measurements of the thermodynamics and kinetics of guest sorption with powderX-ray diffraction measurements of the nanoporous metal organic framework adsorbent (host) at differentadsorptive (guest) loadings. The adsorption characteristics of nitrogen, argon, carbon dioxide, nitrous oxideand ethanol and methanol vapors on Ni2(4,4‘-bipyridine)3(NO3)4 were studied over a range of temperatures asa function of pressure. Isotherm steps were observed for both carbon dioxide and nitrous oxide adsorption at∼10−20% of the total pore volume and at ∼70% of total pore volume for methanol adsorption. The adsorptionkinetics obey a linear driving force (LDF) mass transfer model for adsorption at low surface coverage. At highsurface coverage, both methanol and ethanol adsorption follow a combined barrier resistance/diffusion model.The rates of adsorption in the region of both the carbon dioxide and methanol isotherm steps were significantlyslower than those observed either before or after the step. X-ray diffraction studies at various methanol loadingsshowed that the host structure disordered initially but underwent a structural change in the region of the isothermstep. These isotherm steps are ascribed to discrete structural changes in the host adsorbent that are induced byadsorption on different sites. Isotherm steps were not observed for ethanol adsorption, which followed a Langmuirisotherm. Previous X-ray crystallography studies have shown that all the sites are equivalent for ethanoladsorption on Ni2(4,4‘-bipyridine)3(NO3)4, with the host structure undergoing a scissoring motion and the spacegroup remaining unchanged during adsorption. The activation energies and preexponential factors for methanoland ethanol adsorption were calculated for each pressure increment at which the linear driving force modelwas obeyed. There was a good correlation between activation energy and ln(preexponential factor), indicatinga compensation effect. The results are discussed in terms of reversible adsorbate/adsorbent (guest/host) structuralchanges and interactions and the adsorption mechanism. The paper contains the first evidence of specificinteractions between guests and functional groups leading to structural change in flexible porous coordinationpolymer frameworks.
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