Porous polyvinyl alcohol/biochar hydrogel induced high yield solar steam generation and sustainable desalination

Abstract

Solar vapor generation is one of effective techniques in alleviating freshwater shortages. However, targeted gaps of high-efficient solar harvesting and fast evaporation rate still existed. In this work, the polyvinyl alcohol/biochar hydrogels (PBHs) with different water/PVA ratio were fabricated as the effective solar-driven vapor generator. The openly porous structure facilitated the intense capillary effect and water transport to PBH surface. Moreover, the proportion of intermediate water changed with the water/PVA ratio and further reduced the evaporation enthalpy. The solar absorber on the biochar interface confined the convective heat and reduced the heat loss. These properties induced the generation rate of PBH-10 achieving 1.89 kg m−2 h−1 with the solar-to-vapor convection efficiency of 85.2% under 1 sun irradiation. The thermal conduction well fitted to the heat distribution in the evaporation system according to COMSOL simulation. The rate of water vaporization by PBH-10 also maintained excellent performance in the salt rejection and wastewater purification containing different pollutants. It is anticipated that the PBH evaporator provided new possibilities in the clean water collection, desalination, and wastewater purification under natural sunlight.