Tubular polypyrrole enhanced elastomeric biomass foam as a portable interfacial evaporator for efficient self-desalination

Three-dimensional (3D) materials that capture sunlight for desalination provide one promising solution to acquiring freshwater resources, but salt deposition and mechanical stability provide additional hurdles for continuous operation. Herein, this study presents a sustainable and elastic biomass evaporator (EC-PPy-MO) with the hierarchical micro-nano water transport channel and air cavities formed by hydrophilic tubular polypyrrole seamlessly integrated onto the external surface of biomass foam. The EC-PPy-MO foam exhibits high light absorption ability (∼91%) over a broad wavelength due to the waveguide effect of the polypyrrole with a slender tubular morphology and the hierarchical micro-nano structure in the biomass matrix. The EC-PPy-MO foam helps stabilize a thin water film to provide an efficient evaporative interface surface and ensure effective thermal insulation. As a result, the EC-PPy-MO foam evaporator parallel to the horizontal plane demonstrates a rapid evaporation rate of about 1.8 kg m -2 h −1 under 1 sun irradiation. In parallel, the evaporator can maintain efficient evaporation without salt fouling in a solution with 7% NaCl salinity, while largely salt fouling appears when higher than 15% brine. However, EC-PPy-MO with melamine foam support floating in 25 wt% brine can be evaporated for 72 h without significant salt fouling accumulation, up to ∼ 2.8 kg m -2 h −1. This is attributed to the fact that the exposed sides of the 3D EC-PPy-MO foam can eliminate the boundary Marangoni phenomenon resulting in the appearance of no significant salt fouling, while the exposed cold evaporation surface enhances the evaporation rate of the EC-PPy-MO foam. More importantly, EC-PPy-MO foam exhibits excellent mechanical stability, chemical stability, and elasticity, as well as remarkable water purification ability.