Preparation of Porous Biomimetic Biochar-Based Photothermal Conversion Materials and Development of Air Water Harvesting Devices

Atmospheric water harvesting technology, utilizing photothermal conversion materials and hygroscopic agents, shows great potential for extracting pure water from the air. In particular, photothermal conversion materials derived from agricultural and forestry waste have attracted widespread attention due to their low cost, easy availability, and environmental friendliness. This work investigates the design of a unique photothermal evaporator using a biomimetic method, drawing inspiration from the natural transpiration of trees. Wheat straw biochar (WSB) was used as an efficient photothermal material, deposited on acetate fiber (AF) filter cotton with the assistance of polydopamine (PDA), successfully integrating into a solar photothermal steam generation system. To enhance salt resistance, the material was hydrophobically modified using a fluorocarbon resin emulsion, resulting in a hydrophobic photothermal conversion material called WSB/PDA@AFH. The porous biomimetic WSB/PDA@AFH exhibited excellent light absorption, hydrophobicity, salt resistance, and effective heat localization. Even after 8 h of evaporation cycles with 30 wt % LiCl without salt crystallization, it showed exceptional salt resistance by achieving an evaporation rate of 3.38 kg·m–2·h–1 under one sun irradiation cycle. For continuous desorption, this makes it perfect for liquid hygroscopic systems. Given its actual water harvesting rate of 1.86 L·m–2·d–1, WSB/PDA@AFH dramatically enhanced the desorption performance of 30 wt % LiCl in a portable atmospheric water harvesting system evaluated at 60% humidity. This technology offers a viable alternative to alleviate freshwater resource shortages because of its simple construction process, low cost, eco-friendliness, and efficient use of solar energy.