Structure–Property Discernments from a Hydrophobic Zinc-Diaminotriazolato-Formate Metal–Organic Framework Exhibiting Improved CO2/H2O Binary Characteristics

Abstract

Efficient and selective capture of CO2 under humid conditions is essential for the development of practical carbon capture technologies. Ultramicroporous metal–organic frameworks (MOFs) are particularly promising due to their strong host–guest interactions, which enhance CO2 selectivity. A well-known example is CALF-20, a Zn-triazolate-based ultramicroporous MOF that has demonstrated excellent CO2 capture performance; however, its uptake significantly decreases beyond 40% relative humidity (RH), limiting its use in higher humidity environments. To address this limitation, we present IISERP-MOF16 (Zn-Damtz-Formate), featuring a formate-pillared layered structure with 3,5-diamino-1,2,4-triazole (Damtz) linkers. The idea was to increase the basic nitrogen groups and lower the water-interacting oxygens. The IISERP-MOF16 is structurally analogous to CALF-20. Notably, the formate groups, in situ generated via DMF decomposition, result in the MOF, and the use of any source of zinc results in this phase as long as DMF is employed. Despite this, the phase can be produced on multigram scales with ease. Gas adsorption studies reveal that the MOF exhibits a moderate CO2 uptake of 40.2 cm3/g at 298 K and 1 bar, with an isosteric heat of adsorption (Qst) of 32 kJ mol–1 and an IAST-predicted CO2/N2 selectivity of 67 for a 15:85 (v/v) mixture. Importantly, dynamic vapor sorption measurements indicate that the MOF retains over 20% of its initial CO2 uptake at 70% RH, a level at which CALF-20 shows negligible adsorption. The material also demonstrates excellent stability, recyclability, and easy regeneration under various conditions, aligning well with industrial requirements. Despite all these advantageous features, this MOF is not able to outperform CALF-20 in terms of CO2 capacity. However, by directly comparing the structure and properties of IISERP-MOF16 to those of CALF-20, we can identify specific characteristics that influence CO2 capture efficiency. These insights help guide the targeted design of future humid CO2 capture MOFs within this family.