Hygroscopic Salt in A Mesoporous Zirconium Metal−Organic Framework for Atmospheric Water Harvesting

Abstract

Highly stable zirconium-based metal-organic frameworks (Zr-MOFs) have emerged as promising matrices for constructing "composite salt in porous matrix" (CSPM) adsorbents in atmospheric water harvesting applications, owing to their exceptional chemical and hydrolytic stability. However, current implementations remain largely confined to a limited number of microporous architectures that suffer from restricted pore volumes and suboptimal adsorption kinetics. To address these critical limitations, we present a new entry through the rational integration of hygroscopic CaCl2 into mesoporous NJTech-4 - a Zr-MOF demonstrating remarkable water-vapor cycling stability. Systematic incorporation of calcium chloride with varying loadings (20-50 wt%) enables precise optimization of hygroscopic performance. The engineered composite NJTech-4-Ca10 (38.4 wt% CaCl2 loading) achieves a high water uptake capacity of 610 mg g⁻¹ at 30% relative humidity, representing a 12-fold enhancement over the pristine framework. More significantly, this composite demonstrates fast adsorption-desorption kinetics with a working capacity of 365 mg g⁻¹ within 60 minutes - a critical advancement enabling multiple daily harvesting cycles.