Cellulose helical foam with multi-strategy optical metasurface via synergistic light trapping for superior...

Addressing the critical need for freshwater due to growing global demand requires advanced materials for solar evaporation. Liquid metal (LM) shows excellent potential as a photothermal material, but its use in solar evaporators is hampered by poor light absorption and low efficiency, largely because of surface plasmon resonance. To address this, we chemically modified LM with ellagic acid (EA), significantly improving its visible light absorption through strong interfacial bonding. By formulating nanocellulose-based inks, we fabricated a grid-like micropattern and a helical rising macrostructure. The micropattern enhances light harvesting via multiple internal reflections, while the helical geometry increases both air convection and effective evaporation surface area. This engineered EA-LM/cellulose foam demonstrated outstanding solar evaporation performance. Under one sun illumination, it reached a surface temperature of 70.5 °C within one hour and achieved a high evaporation rate of 1.932 kg·m^-2·h^-1. Moreover, the superiority of 3D evaporator was verified through the related mechanism simulation. By combining molecular-level photothermal enhancement with structural engineering, this approach offers a powerful and sustainable strategy for solar-driven water purification.