Novel efficient solar spherical evaporators with adjustable pores to control water supply and evaporation

Abstract

Solar-driven interfacial evaporation is a promising seawater desalination technique. The limited evaporation rate in evaporators used up to now is due to the poor balance between the water supply, and the evaporation rate at the solar absorber evaporation surface. Here, we report the fabrication of novel and efficient spherical solar evaporators, whose adjustable pore size and porosity accelerate water evaporation. These evaporators are porous coating made of vertical array carbon nanotubes (VACNT) / cellulose nanofibers (CNF) / polyvinyl alcohol (PVA), which are wrapped around light-expanded polystyrene (EPS) spheres. The experimental results show that the drying time and the PVA content decisively determine the pore size and, subsequently, the water content. The optimized evaporators manifest a high evaporation rate of 1.23 kg·m−2·h−1 and efficiency of 76.3 % under 1 sun illumination, which is 3.2 times higher than the evaporation rate of pure water under the same conditions. The fabricated evaporators are applied to produce clean water from simulated seawater, and the results show that the metal ion concentrations in the collected water are far below the upper levels of the WHO (World Health Organization) International Standards.