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

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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.
Funding Information
  • Australian Research Council (DP210100901)

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