Fig. 2: Characterization of iron hydrogel and LEH.
a DFT stimulation of an optimized FeCl3·6H2O unit cell. b Optimized (100) slab configuration for water molecule absorption of a 1 × 2 × 1 iron hydrogel supercell. The brown, green, red, black, silver, and white spheres represent Fe, Cl, O, C, N, and H atoms, respectively. c Water embedding energy of FeCl3·6H2O and the iron hydrogel. The more negative value for the iron hydrogel indicates a stronger water affinity. d Water uptake performance of the iron hydrogel, FeCl3·6H2O and EA under 25 °C, 75% RH. The iron hydrogel exhibited both higher moisture uptake capacity and faster water capture kinetics. e Moisture absorption isotherm of iron hydrogel under different temperatures. f Schematic illustration of the fabrication process of LEH. The preparation process could be summarized into fallen leaves collection, leaf bleaching, conductive treatment, and asymmetrical iron hydrogel coating. g, h SEM images and water contact angle measurements of (g) a pristine green leaf and (h) a white leaf. An inversion of surface wettability was observed after surface bleaching. i, j X-ray CT image of (i) a pristine green leaf and (j) a white leaf, indicating the high porosity of the leaf. k SEM image and water contact angle of a conductive leaf. l Rheological properties of iron hydrogel under hydrate conditions. The storage modulus of the iron hydrogel is higher than the loss modulus, implying a gel-like behavior for water movement restriction. Inset: SEM image of the iron hydrogel with a network structure. m The directional water diffusion images of the iron hydrogel and LiCl after 24 h of moisture absorption at 75% RH. Both solutions are evenly dip-coated in the central square area drawn by the solid line and dried in the oven. n Water content distribution of LEH after moisture absorption. An apparent water gradient across LEH was observed. o Optical, SEM images, and EDS mapping of the LEH. A clear leaf vein is observed, acting as a barrier between the iron hydrogel and the untreated area after asymmetrical coating.
