INFLUENCE OF ZIF-8 AND ZIF-67 MODIFICATION ON THE OF C-H BOND FLEXIBILITY USING NEUTRON ANALYSIS TECHNIQUES

ZIFs, a subclass of MOFs, are composed of transition metals connected by imidazolate molecules. These structures exhibit high porosity and surface area, making them applicable in fields such as catalysis, adsorption, and electrodes. They are particularly effective in CO2 capture and storage, as well as in gas separation based on molecular size. However, the structural flexibility of ZIFs can lead to variations in pore size, impacting their performance. This phenomenon, known as gate-opening, allows gases with kinetic diameters larger than the nominal pore size, such as N₂, to pass through, reducing selectivity for gases like CO2. One of the key advantages of ZIFs is their ease of characterisation through XRD, which provides detailed insights into their crystalline structures. The gate-opening effect observed in ZIF-8 is particularly relevant for industrial gas separation processes, as ZIF-8 can alter its structure in response to external stimuli, such as gas pressure. The gate opening effect increases the pore size reducing the selectivity of ZIF-8. The modification of ZIFs with more rigid ligands such as benzimidazole, and modification with graphene oxide can reduce the gate opening effect and improve the selectivity of ZIFs. INS studies have been employed to investigate the structural deformations of ZIF-8 during the incorporation of N₂ at cryogenic temperatures, revealing the dynamics of methyl and imidazolate groups and experimentally confirming the effect.