(29f) Ferromagnetic MOF-Alginate Hybrid Beads for Atmospheric Water Capture and Induction Heating-Enabled Water Release

With global concern over freshwater scarcity escalating and traditional water supply methods like desalination, facing challenges due to high costs and energy consumption, researchers have diverted their attention to non-traditional water resources such as atmospheric water vapor. Earth’s atmosphere holds 10 % of freshwater in the form of vapor or droplets, which could address global water issues¹.

Various methods, including cooling air below dew point temperature, using desiccants, and employing porous materials like silica gel, zeolites, pristine MOFs, and MOFs impregnated with hygroscopic salts have been proposed for atmospheric water harvesting (AWH)². Among MOFs, sorbents like MOF-801-P, MOF-841, MOF-808, MOF-303 have exhibited promising performance³. However significant challenges persist, particularly in achieving structural forms and efficient water recovery methods⁴. Hybrid structures, like hydrogel-MOF composites, offer a potential solution, with recent innovations including the incorporation of LiCl into polyacrylamide hydrogel and the use of sunlight as a means of efficient energy for water release technology^5,6. However, despite the proven feasibility, low productivity remains a long-standing challenge for solar-driven AWH devices⁷.

In addressing these challenges, this work introduces a novel hybrid ferromagnetic MOF-alginate composite (MOF-AG@IO) beads for atmospheric water harvesting. Synthesized instantaneously at room temperature via ionic gel polymerization technique, the composite beads (MOF-AG@IO) were comprised of a hydrophilic hydrogel network embedded with hydrophilic substances i.e., MOF-808 and CaCl₂, and iron oxide (Fe₃O₄), as magnetic susceptor. SEM-EDX and XRD analysis confirmed the successful incorporation of MOF-808 crystals in the hydrogel together with CaCl₂ and Fe₃O₄ particles. The composite beads exhibited high water capturing capacity from the atmosphere (∼ 1.02 g_H2O/g_MOF-AG@IO, 75 % RH, 25 °C) and, owing to Fe₃O₄ presence, quick water releasing capability (∼ 85 % water release within the first 30 min.) when exposed to magnetic induction, a technology not limited by the natural day-light cycle. Furthermore, it displayed outstanding cyclic stability, enduring up to 10 consecutive cycles. These remarkable performance characteristics translated into an excellent potential water productivity of up to 9.11 L_H2O/kg_MOF-AG@IO/day at 75 %RH, 25 °C and 10.3 L_H2O/ kg_MOF-AG@IO /day in outside conditions (open-air environment, VUB campus, Etterbeek).

Overall, this work presents a new conceptual advance of hybrid composite materials which takes advantage of its constituent properties. The rapid and uniform heating provided by induction heating, a technology not constrained by natural sunlight, positions these findings as an important platform for next-generation electrified water harvesting technologies.

References

1. UN Water & UNESCO. UN Water (2022).

2. Kandeal, A. W. et al. Sustain. Energy Technol. Assessments 52, 102000 (2022).

3. Furukawa, H. et al. J. Am. Chem. Soc. 136, 4369–4381 (2014).

4. Babaei, H. et al. Nat. Commun. 2020 111 11, 1–8 (2020).

5. Kim, H. et al. Science (80-. ). 356, 430–434 (2017).

6. Fathieh, F. et al. Sci. Adv. 4, (2018).

7. Li, T. et al. Nat. Commun. 2022 131 13, 1–11 (2022).