No abstract

BACKGROUND The effect of framework topology on the guest‐induced flexibility of several crystalline zeolitic imidazolate frameworks (ZIF‐7, ZIF‐9, ZIF‐11 and ZIF‐12) was investigated via analysis of experimental nitrogen (N2), carbon dioxide (CO2) and argon (Ar) isotherms at 77 K (N2 and Ar) and 273 K (CO2) for gas pressures up to 0.13 MPa. RESULTS The experimental isotherms of these frameworks were analysed in order to investigate their structural flexibility using gases with kinetic diameters equal to or larger than the diameters of their static pore apertures. The results of gas sorption measurements indicate guest‐induced phase changes for ZIF‐7 and ZIF‐9 (SOD topologies). ZIF‐12 (RHO topology) also shows uptake for gases, despite its pore‐limiting diameter being smaller than the kinetic diameters of the adsorbed molecules. CONCLUSIONS This work highlights the ability of ZIFs with different framework topologies to change their structure and increase their pore aperture upon interaction with certain gases. These findings are key in the development of more selective ZIF‐based materials for important industrial applications including low‐energy gas separations, catalytic nanoreactors and sensor technology. © 2019 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The adsorption of CO2 on several microporous materials has been measured at various temperatures (263, 273, 283, and 293 K) over a wide range of pressures. The porous materials studied were three zeolites (5A, 13A, and 13X), two metal–organic frameworks (Basolite A100 and Basolite Z1200), an activated carbon, and two pillared clays (Al-PILC and Zr-PILC). The data obtained were fitted to the Freundlich, Langmuir, and Toth isotherms. Various methods were used to calculate the Henry’s law constants. The values found for the zeolites, which ranged from 8.95 to 36.02 mmol/kPa·g at 273 K, were much higher than those for the metal–organic frameworks, activated carbon, and pillared clays, which ranged from 0.012 to 0.200 mmol/kPa·g at the same temperature. The isosteric heats of adsorption of CO2 on the materials were calculated using the Clausius–Clapeyron equation, and the adsorbent–CO2 affinity was found to increase in the order Z1200 ≈ 13X ≈ 13A < 5A < Zr-PILC < A100 ≈ AC ≈ Al-PILC at low loadings.