Hydrolytically Stable Zinc-triazole-dicarboxylates for Atmospheric Water Harvesting Formed by In Situ Isomerization of Itaconic Acid

Atmospheric water harvesting (AWH) is an effective strategy to address water scarcity in arid regions, but the key challenge lies in developing adsorbents that can efficiently capture water at low relative humidity, while enabling facile release with minimal energy input. Herein, three mixed-ligand MOFs, Zn-mfa-atz-1, Zn-mfa-atz-2, and Zn-mfa-tz, were synthesized using low-cost ligands, itaconic acid (H₂ic) and 3-amino-1,2,4-triazole (Hatz) or 1H-1,2,4-triazole (Htz). During the syntheses, H₂ic underwent in situ isomerization into (E)-2-methylfumaric acid (H₂mfa). The MOFs are all 3D framework structures, and Zn-mfa-atz-2 and Zn-mfa-tz are isostructural. Zn-mfa-atz-1 and Zn-mfa-atz-2 exhibit permanent porosity (BET surface areas of 353 and 379 m²g⁻¹, respectively) and high stability in liquid water at room temperature for 1 week. Their water vapor adsorption isotherms are reversible, with moderate uptakes at P/P₀ < 40% and relatively low adsorption heats (38 to 54 kJ mo⁻¹). Under a low H₂O partial pressure of 1.7 kPa, the two MOFs deliver stable water harvesting capacities of 0.08 and 0.11 g g⁻¹ at an adsorption temperature of 32 °C (RH = 35.7%) and a desorption temperature of 60 °C (RH = 8.5%). While the working capacities are not high, the MOFs offer an advantage in terms of material cost.