Unveiling the oxygen adsorption potential of ZIFs: investigating the impact of organic ligands, metal centres, and synthesis methods

Abstract

Zeolitic imidazolate frameworks (ZIFs) have emerged as promising candidates for high O₂ adsorption capacity, O₂/N₂ selectivity and cyclability due to their tunable chemical and structural properties governed by the selection of organic ligands, metal centres and synthesis methods. Therefore, this research engineers ZIF-7, ZIF-8, ZIF-62 and their mixed-metal derivatives containing cobalt (Co) or iron (Fe) (ZIF-8-derived Fe-mIM where applicable) to improve O₂ adsorption. Because performance metrics trade off, no single ZIF maximised all objectives, and application-specific leads were identified. The highest O₂ capacity was delivered by ZIF-8(Zn : Co = 90 : 10)-MS, reaching 0.35 mmol g⁻¹ with selectivity of 2.01, and 9.9% decrease over 3 cycles. The greatest selectivity was achieved by ZIF-8-derived Fe-mIM material (Zn : Fe = 0 : 100)-MS, giving selectivity of 2.60 at a low adsorption of 0.09 mmol g⁻¹ and 9.6% loss over 3 cycles. The most robust 3-cycle performance was observed for ZIF-8-US, which retained capacity with 0.5% loss while providing 0.26 mmol g⁻¹ and selectivity of 1.06. For a balanced generalist over 3 cycles, ZIF-62-US offered the strongest overall combination, providing 0.34 mmol g⁻¹, selectivity of 1.01, and 1.3% loss. These results underscore the delicate balance among O₂ adsorption performance with structural integrity, coordination chemistry, adsorption characteristics, and cyclability in ZIFs shaped by organic ligand, metal centres, and synthesis method choices.