Enhancing water release in atmospheric water harvesting systems by mixing oligomeric liquids with metal–organic framework

Abstract

Global water access issues and growing energy demands necessitate advanced water-extraction technologies such as atmospheric water harvesting (AWH). However, conventional AWH systems often require intensive energy input for water desorption, which limits their practical application. This study focuses on reducing the desorption temperature to increase the water-release efficiency of AWH systems by using a metal–organic framework (MOF) and an oligomeric liquid-based composite. Our approach leverages the high water-adsorption capacity of MOF303 (Al(OH)(pzdc), pzdc²⁻: 1H-pyrazole-3,5-dicarboxylate), along with its structural stability, while increasing the dehydration rate and reducing the desorption enthalpy. We found that the composite of MOF303 and poly(propylene glycol) with an average molecular weight of 400 (PPG400), along with other oligomers, is a strategic choice for efficient water recovery owing to the hydrophilicity-difference-induced water transfer (HWT) mechanism from the nanopores of the MOF to the liquid oligomer. The thermodynamic behaviour of water desorption in these composites was investigated, and MOF303-PPG400 (1 : 1 weight ratio) composites exhibited an approximately 36 °C decrease in water-desorption temperature compared with pure MOF303, which indicated that the material properties were optimised, reducing the heat energy. This study contributes to the development of sustainable and low-energy AWH systems that can be applied in arid regions and off-grid water sources using only low-grade heat sources.