Anisotropic Biomass Microfluidics via Directed Moisture Transport and Enhanced Water-Binding Capacity for High-Yield Solar-driven Atmospheric Water Harvesting.

Abstract

Solar-driven adsorption-desorption-based atmospheric water harvesting (AD-AWH) presents a promising strategy for sustainable freshwater production. However, conventional hygroscopic materials typically feature disordered internal architectures, severely hindering vapor diffusion and heat transfer. These structural limitations constrain adsorption kinetics and elevate the energy demand for desorption. Here, we report a biomass-based hygroscopic aerogel (BHA) with vertically aligned microfluidic channels, fabricated via directional freeze-drying. This anisotropic architecture enables directed vertical moisture transport combined with radial diffusion into secondary pores, effectively reducing vapor transport tortuosity while simultaneously increasing water-binding capacity. As a result, the BHA achieves a high-water uptake of 3.18 g g^-1 at 80% RH and a rapid adsorption rate of 0.25 g g^-1 within 6 h at 30% RH. Upon surface modification with a photothermal ink, the evaporation rate increases to 2.89 kg m^-2 h^-1, and the desorption ratio reaches 76.63% under one sun irradiation. Outdoor field tests confirm a high daily water yield of 1.51 L m^-2 day^-1. Furthermore, the incorporation of montmorillonite significantly reinforces the mechanical robustness of the aerogel. This work presents a structurally engineered strategy for optimizing internal fluidic and thermal dynamics in hygroscopic materials, offering a scalable and energy-efficient pathway for AD-AWH in water-stressed regions.