Ferromagnetic metal organic framework (MOF)/alginate hybrid beads for atmospheric water capture and induction heating-enabled water release

Atmospheric water harvesting (AWH) using sorbents has been proposed as a promising alternative to tackle the pressing issue of freshwater scarcity, particularly in densely populated metropolitan cities. However, successful deployment of this technology hinges on two critical prerequisites: high water capture capacity and low energy consumption for quick water release. In this work, a novel hybrid ferromagnetic MOF-alginate composite (MOF-AG@IO) bead for atmospheric water harvesting is presented. Using an ionic gel polymerization technique, instantaneous formation of MOF-AG@IO bead was achieved. SEM-EDX and XRD analysis revealed successful incorporation of MOF-808 crystals in the hydrogel together with CaCl2 and Fe3O4 particles. The composite exhibited high water capturing capacity from the atmosphere (∼ 1.02 gH2O/gMOF-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. The composite also showed cyclic stability, high water uptake kinetics (∼0.8 g/g at 75 % RH and 25 °C within 4 h) and excellent feasible water productivity of ∼9.11 LH2O/kgMOF-AG@IO/day. This potential productivity surpasses any previously reported values for MOF and MOF composites. Further, the composite sorbent exhibited high stability in outdoor conditions with no decline in water uptake capacity for multiple cycles. In summary, the novel ferromagnetic composite, which demonstrates a synergy of its constituent properties, offers itself as an attractive candidate for next-generation water harvesting devices integrated with electrified heating technology.