Optimizing iron-based metal-organic frameworks for adsorption water harvesting: A comparative evaluation of green and conventional MIL-100(Fe) synthesis

The increasing scarcity of freshwater is a critical global challenge, positioning Atmospheric Water Harvesting (AWH) as a promising technology for decentralized water production. Metal-Organic Frameworks (MOFs), particularly the iron-based MIL-100(Fe), have shown immense potential for AWH due to their high surface area and step-shaped adsorption isotherms. Although greener synthesis routes for MIL-100(Fe) have been reported to reduce environmental impact, their specific application to gas-phase water harvesting remains largely unexplored. This study investigates the synthesis of MIL-100(Fe) via two distinct pathways: a conventional high-temperature hydrothermal method and a milder green synthesis approach carried out under ambient-temperature conditions. The results show that the green route provides an effective strategy for improving AWH-relevant properties while reducing the severity of the synthesis conditions. Characterization data reveal that the MOF obtained through the green strategy exhibits superior crystallinity and a significantly higher water-harvesting uptake compared to the conventional reference. In detail, the dynamic vapor sorption analysis demonstrated a maximum water uptake of 0.53 g/g in the first cycle and 0.48 g/g in the third cycle for G-M100Fe, whereas T-M100Fe exhibited an uptake of 0.47 g/g in the first cycle and 0.39 g/g in the third cycle under identical conditions. Although both samples showed a decrease in capacity over the first three cycles, the lower loss between the second and third cycles suggests a reduced degradation rate after the initial conditioning stage. By linking milder synthesis conditions with enhanced functional performance, this work identifies green-synthesized MIL-100(Fe) as a promising candidate for MOF-based atmospheric water harvesting applications.