Tunable Low‐Pressure Water Adsorption in Stable Multivariate Metal‐Organic Frameworks for Boosting Water‐Based Ultralow‐Temperature‐Driven Refrigeration

Abstract

AbstractThe green water‐based adsorption refrigeration is considered as a promising strategy to realize near‐zero‐carbon cooling applications. Although many metal‐organic frameworks (MOFs) have been developed as water adsorbents, their cooling performance are commonly limited by the insufficient water uptakes below P/P0 = 0.2. Herein, the development of multivariate MOFs (MTV‐MOFs) is reported to highly modulate and boost the low‐pressure water uptake for improving coefficient of performance (COP) for refrigeration. Through ligand exchange in the pristine MIL‐125‐NH2, a series of MTV‐MOFs with bare nitrogen sites are designed and synthesized. The resulting MIL‐125‐NH2/MD‐5% exhibits the significantly improved water uptake of 0.39 g g−1 at 298 K and P/P0 = 0.2, which is three times higher than MIL‐125‐NH2 (0.12 g g−1) and comparable to some benchmark materials including KMF‐1 (0.4 g g−1) and MIP‐200 (0.36 g g−1). Combined with its low‐temperature regeneration, fast sorption kinetics and high stability, MIL‐125‐NH2/MD‐5% achieves one of the highest COP values (0.8) and working capacities (0.24 g g−1) for refrig‐2 under an ultralow‐driven temperature of 65 °C, which are higher than some best‐performing MOFs such as MIP‐200 (0.74 and 0.11 g g−1) and KMF‐2 (0.62 and 0.16 g g−1), making it among the best adsorbents for efficient ultralow‐temperature‐driven refrigeration.