Zeolitic Imidazolate Frameworks (ZIFs) for Aqueous Phase Adsorption – A Review

Abstract Zeolitic Imidazolate Frameworks (ZIFs) represents a subclass of the metal-organic frameworks (MOFs), composed mainly of tetrahedrally coordinated transition metals. The aim of this review was to evaluate the experimental findings on the adsorption of different aqueous pollutants using ZIFs. ZIF adsorption mechanism was electrostatic attraction, π-π interaction and complexation though others were observed based on pollutant type and nature of the solution chemistry. Thermodynamic modelling revealed that ZIF adsorption is usually spontaneous and endothermic. The adsorbent can be re-used for 3-4 cycles with >70% retention of uptake performance. NaOH, methanol and ethanol were observed to be the more suitable and effective eluents for desorption of adsorbate from ZIF. The nature of the adsorbate and the type of uptake mechanism are the two key considerations in competitive adsorption systems. When the uptake mechanism of the main adsorbate species is different from that of the competing species, then the adsorption process is unaffected. Investigations on adsorbent disposal, targeted modification, functionalisation, emerging contaminants removal, column adsorption studies and molecular modelling would be needed to fill in gaps in knowledge in ZIF related studies.