A self-regenerating 3D sponge evaporator with a tunable porous structure for efficient solar desalination

Abstract

Three-dimensional (3D) solar evaporators are known to possess high evaporation rates, typically exceeding the theoretical limit of conventional evaporators. However, salt fouling remains a challenging issue that plagues 3D evaporators. Herein, we demonstrated bio-based 3D sponge solar evaporators with tailored porous architectures, fabricated with chitosan (CS), agarose (Aga) and multiwalled carbon nanotubes (MW). By merely manipulating the CS to Aga ratio, the pore structures of the sponge can be tuned. As such, an evaporator (5CS/Aga-MW) exhibits impressive evaporation rates of 2.24 and 3.07 kg m⁻² h⁻¹, for 30 mm and 60 mm height, based on additional energy gained from the surrounding environment, which exceeded theoretical limit for conventional 2D evaporators. More importantly, evaporation performance using saline water with 3.5% salinity shows a stable evaporation rate of ∼3.04 kg m⁻² h⁻¹ for the first 2 days for a height of 60 mm, and ∼2.19 kg m⁻² h⁻¹ throughout 10 consecutive days for a height of 30 mm, demonstrating superior anti-salt-fouling ability with an impressive evaporation rate. The excellent performance was attributed to its unique mixed pore structure with low tortuosity, which provided sufficient water supply and the ability to balance out the salt concentration gradient quickly. Such a bottom-up approach in designing 3D evaporators could be an important pathway for the fabrication of efficient 3D-structured evaporators that possess high evaporation performance along with anti-salt-fouling ability.