Robust Bioinspired Microcellular and Micro-Nanochannel Photothermal Aerogels for High-Efficiency Atmospheric Water Harvesting

A strategy for atmospheric water harvesting to address the global shortage of freshwater has received much more attention in recent years. Here, we design a robust microcellular and micro-nanochannel photothermal aerogel (MMPA) for atmospheric water harvesting, inspired by the xylem of conifers, which is realized by directional freeze-drying and the Ca²⁺ ion cross-linking technique. MMPA can be designed by using hollow MIL-101 (Cr), cellulose acetate nanofibers, sodium alginate, and polypyrrole. Such a MMPA is endowed with a water harvesting effect due to the high specific surface area that resulted from microcellular and micro-nanochannels with water molecule hydrophilic sites for capturing moisture from air. The MMPA realizes a water uptake capacity, e.g., ∼0.73 g g^-1 at 40% relative humidity (RH). MMPA can be increased to ∼85 °C after 5 min under 1 sun (1 kW m^-2) illumination for a water release effect, e.g., water release reaches ∼75% under 1 sun irradiation for 40 min. MMPA can keep the stability of water uptake-release over 50 cycles. In 1 day outdoors, the total water uptake achieves up to ∼7.84 L kg^-1 day^-1, along with the 9 cycles of uptake-release, accordingly, achieving a water harvesting ability of ∼5.49 L kg^-1 day^-1 under natural light irradiation. This study offers an insight into the design of materials, which can be extended for water harvesting applications.