Controlling pore size and photothermal layer to improve solar-porous evaporation performance

Solar desalination, harvesting solar energy to purify seawater, has received considerable attention due to water scarcity problems caused by climate change and human activity. In this study, we investigated a membrane desalination method that collects vaporized water from the surface of a sun-lit porous medium floating on salt water. To maximize the water evaporation rate at the membrane surface, several effective photothermal converting materials were coated on the membrane. In addition, to amplify the water transport to the sun-lit surface, the pore size of the porous medium also was controlled by filtering sugar particles by size. We found that the evaporation rate increased as the reflectivity of the coating materials decreased, and demonstrate the optimized pore size, leading to improved evaporation at the three-phase interface by controlling the size of the pores. The water transport is caused by the porous medium resulted from competition between capillary and viscous forces; thus, the optimal pore size for maximum water transport and evaporation rate is discussed. The finding of this study provide insight into optimizing the design of the membrane’s structure and coating materials to maximize the evaporation rate in solar desalination.