Corn straw coated with Fe3+-tannic acid bilayers as a photothermal material for solar steam generation

Recently, studies on developing a system to filter seawater into clean water using the method of water evaporation at the interface of photothermal materials and air using solar energy (solar steam generation - SSG) have attracted increasing attention from the scientific community. In those SSG systems, photothermal materials play a key role in improving water evaporation rate and efficiency. In this study, a photothermal material was fabricated by treating the corn straw with tannic acid and Fe3+ solution (cheap and environmentally friendly). The surface of photothermal material from corn stalks exhibited a good ability to absorb over 90% of light with wavelengths of 300-1500 nm due to the formation of a complex layer between Fe3+ ions and hydroxy groups (OH) of tannic acid with sizes of 200-1000 nm. Besides, corn straw consists of many vascular bundles and porous multilayers that exhibit a honeycomb-like structure, which improves the ability of water transportation and reduces the thermal conductivity of the material. Therefore, an SSG system utilising the photothermal material based on corn straw possesses a high-water evaporation efficiency of 1.58 kg m-2 h-1. This efficiency was stably maintained for a long time due to the durability of corn straw in various conditions. The corn straw-based photothermal material showed high potential for SSG utilising seawater desalination method with affordable fabrication cost and eco-friendly raw materials.