Surface-Carbonized Bamboos with Multilevel Functional Biostructures Deliver High Photothermal Water Evaporation Performance

Interfacial solar steam generation (ISSG) has attracted global attention as an important approach for water purification and desalination. The related photothermal materials based on 3D biostructures are promising due to their abundance and easy accessibility. Here, it is shown that surface-carbonized bamboo (SC-bamboo) as a photothermal material exhibits outstanding ISSG performance due to its multilevel functional biostructures. On a microscopic scale, the bamboo's air-filled parenchyma cells promote thermal insulation while its vascular bundles ensure rapid water transport. On a macroscopic scale, a unique concave structure at the bamboo nodes concentrates water and heat in a confined region and the air-filled hollow chambers in bamboo internodes also ensure thermal insulation. These multilevel functional structures of SC-bamboo result in a solar-thermal conversion efficiency up to 93.63% ± 1.57% under 1 kW m⁻² irradiation, surpassing most biomass-derived materials ever reported. Considering bamboo's low cost and convenience, this work sheds light on the design and fabrication of readily accessible, multilevel functional structure for efficient photothermal-conversion devices.