Metal–Organic Framework Flexibility Boosting Atmospheric Water Harvesting by a Zinc-Based Glycine–Glyoxime–Histidine Framework

Abstract

Structural flexibility of metal–organic frameworks (MOFs) is both a challenge and an opportunity, depending on the MOF’s properties and the proposed applications. Here, we focus on ZnGGH, a peptide-based flexible MOF that switches from its “gate-closed” ZnGGH-9 conformer to “gate-open” ZnGGH-4 upon water adsorption. We use periodic density functional theory (DFT), semiempirical self-consistent charge density functional tight binding third order (DFTB3) and neural network-based MACE-MP simulations to understand the ZnGGH’s behavior and assess its potential for atmospheric water harvesting (AWH). Our results show that ZnGGH selectively adsorbs water over CO2, O2, and N2. As water loading increases, water-linker interactions trigger the gate opening and affect temperature-dependent water diffusion within the pores. Based on our analyses and comparison with benchmark AWH MOFs (MOF-303, MOF-333 and MOF-808), the gate opening facilitates AWH by weakening of the water interactions during water adsorption/desorption cycles while maintaining water selectivity. The MOF is thermally and hydrolytically stable under AWH conditions. To enable grid-scale applications, future work should focus on reducing synthesis costs to improve its economic viability.