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Water scarcity and waste mismanagement are global crises that threaten the health of populations worldwide and a sustainable future. In order to help mitigate both these issues, a solar desalination device composed entirely of fallen leaves and guar – both natural materials – has been developed and demonstrated herein. This sustainable desalinator realizes an evaporation rate of 2.53 kg m −2 h −1 under 1 sun irradiance, and achieves consistent performance over an extended exposure period. Furthermore, it functions efficiently under a variety of solar intensities and in high salinity environments, and can produce water at salinities well within the acceptable levels for human consumption. Such strong performance in a large variety of environmental conditions is made possible by its excellent solar absorption, superb and rapid water absorption, low thermal conductivity, and considerable salt rejection abilities. Composed primarily of biowaste material and boasting a simple fabrication process, this leaf-guar desalinator provides a low-cost and sustainable avenue for alleviating water scarcity and supporting a green path forward. 

Solar-driven interfacial evaporation shows great prospects for seawater desalination with its rapid fast evaporation rate and high photothermal conversion efficiency. Here, a sustainable, biodegradable, non-toxic, and highly efficient full ocean biomass-based solar-driven evaporator is reported, which is composed of chitosan (CS) hydrogel as the hydratable skeleton and cuttlefish ink (CI) as the photothermal material. Under solar irradiation, the cuttlefish ink powder harvests solar energy and heats the surrounding water. Simultaneously, the water in the three-dimensional network of chitosan hydrogel is rapidly replenished by the interconnected porous structure and the hydrophilic functional groups attached to the polymer chains. With its enlarged evaporation surface, high solar absorptance, adequate water transportation, good salt drainage, and heat localization, the CI/CS-based evaporator achieves a remarkable evaporation rate of 4.1 kg m −2 h −1 under one sun irradiance (1 kW m −2 ) with high-quality freshwater yields. This full ocean biomass-based evaporator with abundant raw material availability provides new possibilities for an efficient, stable, sustainable, and environmentally friendly solar evaporator with guaranteed water quality. 

Abstract Solar‐driven steam generation, whereby solar energy is harvested to purify water directly, is emerging as a promising approach to mitigate the worldwide water crisis. The scalable application of conventional 3D evaporators is hindered by their complex spatial geometries. A 2.5D structure is a spatial extension of a 2D structure with an addition of a third vertical dimension, achieving both the feasibility of 2D structure and the performance of 3D structure simultaneously. Here, an interconnected open‐pore 2.5D Cu/CuO foam‐based photothermal evaporator capable of achieving a high evaporation rate of 4.1 kg m⁻²h⁻¹under one sun illumination by exposing one end of the planar structure to air is demonstrated. The micro‐sized open‐pore structure of Cu/CuO foam allows it to trap incident sunlight, and the densely distributed blade‐like CuO nanostructures effectively scatter sunlight inside pores simultaneously. The inherent hydrophilicity of CuO and capillarity forces from the porous structure of Cu foam continuously supply sufficient water. Moreover, the doubled working sides of Cu/CuO foam enlarge the exposure area enabling efficient vapor diffusion. The feasible fabrication process and the combined structural features of Cu/CuO foam offer new insight into the future development of solar‐driven evaporators in large‐scale applications with practical durability.