Bioinspired Photothermic MOF-Spindle-Knot Microfibers with Ultrafast Uptake–Release for Atmospheric Freshwater Harvester

A bioinspired photothermic MOF-spindle-knot microfiber (BPMM) is designed by using polyisopropylacrylamide, α-polyvinylidene fluoride as-grown metal-organic framework (MOF-303), and carbon black. A mechanism of water harvesting is related to the integrative effects of chemical and structural, i.e., BPMM composed of periodic-distributed MOF-spindle-knot with rough curvature gradient features, displaying the three-dimensional skeleton with porous channel and high-hydrophilic sites and photothermal responsive hydrophilic-hydrophobic switches as well, which runs a synergistic effect to achieve an ultrahigh water uptake-release and propel water-molecule capture in high efficiency under atmospheric low humidity. BPMM takes on ∼ 100% of water release under 1 sun for as-uptaked water and, accordingly, achieves the water harvesting capability of ∼0.16-0.62 g g^-1 h^-1 at ∼25 °C and ∼10-60% relative humidity (RH), which outperforms 2-8 times higher than that of normal MOF-303 or other fibers. BPMM maintains 72 cycles day^-1, achieving water harvesting capability of ∼12.27 g g^-1 in ∼10% RH, under 1 sun. As outdoor at ∼33.4 °C with ∼42.7% RH and ∼0.66 kW m^-2, BPMM reaches water harvesting capability of ∼24.71 g g^-1 day^-1. This finding provides an insight into the design of supermaterials, which would be extended into some realms, e.g., water engineering, energy system, sensor devices in situations with water scarcity, etc.