When Polymorphism in Metal-Organic Frameworks Enables Water Sorption Profile Tunability for Enhancing Heat Allocation and Water Harvesting Performance.

The development of thermally driven water-sorption-based technologies relies on high-performing water vapor adsorbents. Here, polymorphism in Al-metal-organic frameworks is disclosed as a new strategy to tune the hydrophilicity of MOFs. This involves the formation of MOFs built from chains of either trans- or cis- μ-OH-connected corner-sharing AlO 4 (OH) 2 octahedra. Specifically, [Al(OH)(muc)] or MIP-211, is made of trans, trans-muconate linkers and cis-μ-OH-connected corner-sharing AlO 4 (OH) 2 octahedra giving a 3D network with sinusoidal channels. The polymorph MIL-53-muc had a tiny change in the chain structure that results in a shift of the step position of the water isotherm from P/P 0 ∼ 0.5 in MIL-53-muc, to P/P 0 ∼ 0.3 in MIP-211. Solid-state NMR and Grand Canonical Monte Carlo revealed that the adsorption occurs initially between two hydroxyl groups of the chains, favored by the cis-positioning in MIP-211, resulting in a more hydrophilic behavior. Finally, theoretical evaluations showed that MIP-211 would allow achieving a coefficient of performance for cooling (COPc) of 0.63 with an ultralow driving temperature of 60°C, outperforming benchmarks sorbents for small temperature lifts. Combined with its high stability, easy regeneration, huge water uptake capacity, green synthesis, MIP-211 is among the best adsorbents for adsorption-driven air conditioning and water harvesting from the air. This article is protected by copyright. All rights reserved.