Flexible ZIFs: probing guest‐induced flexibility with CO₂, N₂ and Ar adsorption

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.

Phosphotungstic acid grafted zeolite imidazolate framework as an effective heterogeneous nanocatalyst for the one‐pot solvent‐free synthesis of 3,4‐dihydropyrimidinones

“…Broadening of some diffractions would be due to homogeneous dispersion of PTA on the surface of ZIF. However, a slight shift in some peak positions would be explained based on the dispersion of PTA over the surface of ZIF‐9 and considerable interaction of PTA with the surface of ZIF‐9 which may induce partial changes in the crystal structure of ZIF‐9 . Observation of no diffraction peak for PTA in Figure b confirmed that the PTA was highly dispersed on ZIF‐9(NH 2 ) .…”

“…According to these structural information, XRD patterns of bare ZIF‐9(NH 2 ) and PTA@ZIF‐9(NH 2 ) were investigated (Figure ). XRD patterns of the synthesized ZIF‐9(NH 2 ) and PTA@ZIF‐9(NH 2 ) were in good agreement with the reported XRD of ZIF‐9 . The two sharp peaks at 2θ < 10° in the XRD of bare ZIF‐9(NH 2 ), demonstrated that a highly crystalline material was obtained.…”

“…However, previous reports on ZIF‐9 recommended that the pores are complex and may involve both micropore and mesopore arrays . Moreover, grafting of PTA into the cage of ZIF may induce some demolition of ZIF‐9 crystal structure and particles aggregation as shown in Figure b …”

“…The nitrogen adsorption–desorption isotherms of ZIF‐9(NH 2 ) sample measured at 77 K is shown in Figure S2. The type IV isotherm for ZIF‐9(NH 2 ) along with a hysteresis loop at P/P 0 = 0.85–1 with an abrupt increase of gas adsorption at the mentioned relative pressures denoted the mesopores and macropores of the material . The specific surface area of ZIF‐9(NH 2 ) calculated by the BET method was 407 m 2 .g −1 .…”

In Focus: Emerging leaders in future materials for energy and environmental applications

“…In this regard, carbon dioxide can act as a valuable chemical and studies into efficient ways for separating it from the gas stream are essential. Nogueara-Diàz et al 5 have studied the role of framework topology on adaptable separation of CO 2 on a number of the porous metal-organic compounds. They demonstrated adaptability of the CO 2 molecule within the framework structure which could allow for improved gas storage characteristics.…”