Comparative analysis of water adsorption capacity and cyclic stability of solvent-based and solvent-free MIL-101(Cr) for atmospheric water harvesting

Water scarcity represents a major global challenge, affecting millions of people worldwide. Sorbent-based atmospheric water harvesting (SAWH) using metal–organic frameworks (MOFs) has emerged as a promising approach to mitigate this issue. However, the use of expensive and hazardous solvents in conventional MOF synthesis restricts large-scale applications. In this study, MIL-101(Cr) was synthesized through a solvent-free method, exhibiting high water adsorption capacity, rapid desorption behavior, and excellent cyclic stability, enabling solar-driven AWH across a broad range of relative humidity (RH). X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) analyses confirmed the successful formation of solvent-free MIL-101(Cr) with a large specific surface area. The solvent-free material showed a 15% higher adsorption potential than its solvent-based counterpart, achieving a water uptake capacity of 0.547 g/g at 35% RH and 25 °C. 94.6% desorption was attained within 15 min at 70 °C, indicating suitability for low-energy, solar-thermal regeneration. Moreover, the green-synthesized material retained 93% of its adsorption capacity over 30 consecutive adsorption–desorption cycles. These findings demonstrate the potential of solvent-free MIL-101(Cr) as a cost-effective, durable, and sustainable sorbent for AWH applications.