Gate opening effect of zeolitic imidazolate framework ZIF-7 for adsorption of CH₄ and CO₂ from N₂

Abstract

Measurements of S-shaped adsorption isotherm as evidence of ZIF-7 gate opening in the presence of CH4 at 1245 kPa.

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

“…This second step was reported in the paper to be associated with the rearrangement of CO 2 molecules in the pores of the large‐pore phase. More recently, methane (CH 4 ) also was shown to induce gate‐opening in ZIF‐7, with the transition estimated at 1245 kPa for CH 4 and 78 kPa for CO 2 , both at 303 K . This reversible transition also was assigned to the flexibility of the benzimidazole linkers, which enable a large‐pore phase that can allow molecules of 0.52 nm diameter to enter the main cavities.…”

“…19 This second step was reported in the paper to be associated with the rearrangement of CO 2 molecules in the pores of the large-pore phase. More recently, methane (CH 4 ) also was shown to induce gate-opening in ZIF-7, with the transition estimated at 1245 kPa for CH 4 and 78 kPa for CO 2 , both at 303 K. 17 This reversible transition also was assigned to the flexibility of the benzimidazole linkers, which enable a large-pore phase that can allow molecules of 0.52 nm diameter to enter the main cavities. In addition to CO 2 and CH 4 , other molecules have been shown to induce a phase-change in ZIFs -in our past work we have shown this effect for hydrogen (H 2 ) adsorption in ZIF-7 and ZIF-9, 20 and other reports showed phase changes upon adsorption of ethane, ethylene, propane, propene, butane and butene in ZIF-7.…”

“…This structural change was subsequently studied using high‐resolution neutron diffraction, and the analysis showed the importance of the rotation of the benzimidazole linkers . The pore windows of ZIF‐7 are c .0.29 nm in the small pore configuration and can allow molecules of 0.52 nm in diameter when they are in the large‐pore phase . Carbon dioxide (CO 2 ) is adsorbed primarily in two small cavities formed by the benzimidazole linkers in the six‐membered rings of Zn atoms, which rotate upon CO 2 adsorption and open the cavities to accommodate further CO 2 molecules .…”

“…16 The pore windows of ZIF-7 are c.0.29 nm in the small pore configuration and can allow molecules of 0.52 nm in diameter when they are in the large-pore phase. 17 Carbon dioxide (CO 2 ) is adsorbed primarily in two small cavities formed by the benzimidazole linkers in the six-membered rings of Zn atoms, which rotate upon CO 2 adsorption and open the cavities to accommodate further CO 2 molecules. 16 These phase transitions were investigated, and at least three different phases for ZIF-7 were identified.…”

Zeolite imidazolate framework (ZIF)‐based mixed matrix membranes for CO2 separation: A review

“…Notably, its pore size is approximately 3 Å; thus, the narrow pore size facilitates the separation of the CO 2 /H 2 gas pair . Similarly, the “gate‐opening effect” of ZIF‐7, undergoing a reversible phase change to a large‐pore (5.2 Å) phase, has been observed in the adsorption process for H 2 , CO 2 , ethylene, and so forth . Although such an effect would have a negative influence on the gas selectivity, it also offers the possibility to tailor the pore size to different systems under various conditions.…”