Partially carbonized watermelon flesh-based 3D evaporator enhanced by side heat absorption for efficient seawater desalination

Three-dimensional (3D) carbon materials have shown great potential in solar interface evaporation devices, but salt deposition and low evaporation efficiency significantly hinder their continuous operation under seawater conditions. This work presents an all-in-one and sustainable all-biomass evaporator with unique structural advantages, in which the space between the watermelon fibers acts as micro/nanopores water transport channels, while carbonized nanosheets formed onto the outer surface transform absorbed sunlight to heat. As a result, the biomass foam evaporator achieved an excellent evaporation rate of up to 2.35 kg·m⁻²·h⁻¹ in pure water and 2.0 kg·m⁻²·h⁻¹ in 3.5 wt% NaCl solution under 1 sun irradiation, and similarly exhibited a high efficiency and stable operation and superior anti-salt performance in 25 wt% NaCl solution, as well as a remarkable wastewater purification performance. This is attributed to the fast water replenishment facilitated by multi-layered porous structures and hydrophilic groups, efficient thermal management provided by the three-dimensional cylindrical shape, and the capture of environmental energy from the cold side surface of the 3D evaporator. This research not only highlights the potential of incompletely carbonized watermelon as a low-cost biomass material for seawater desalination during solar steam generation but also provides insights for improving the water transport properties of 3D biochar evaporators.