Self-driven super water vapor-absorbing calcium alginate-based bionic leaf for Vis-NIR spectral simulation

Most bionic leaves cannot autonomously absorb water and maintain high water content like plant leaves, causing the low Vis-NIR spectral similarity to plant leaves. Herein, inspired by the transpiration of plant leaves, a self-driven water vapor-absorbing bionic leaf was prepared by the crosslinking between hygroscopic CaCl2 and sodium alginate (SA) on the visible spectral simulating materials (VSSM). Based on the synergistic effect of the hygroscopicity of CaCl2 and the hydrophilia of calcium alginate (CaAlg), the bionic leaf automatically absorbed water vapor from the air according to ambient humidity and temperature. The water vapor-absorbing property of the bionic leaf was adjusted by changing the CaCl2 concentration (5 wt%-40 wt%), and stable water content of 9.0 %-43.3 % can be obtained in relative humidity of 40-80 %. The CaAlg-based bionic leaf embodied a high spectral correlation coefficient (rm ~ 0.987) for the Vis-NIR spectral simulation of plant leaves. The self-driven water vapor absorbing bionic leaves prepared by CaAlg and CaCl2 provide new insights for the application of bionics, water harvesting from the air, environmental humidity management, and camouflage.