Three dimensional hydrogel evaporator made of nano level antireflection particles for high-efficiency solar steam generation

Solar-driven interface evaporation technology provides a sustainable green method for the acquisition of freshwater resources. In this article, a hydrogel of a three-dimensional porous structure has been synthesized for solar steam generation. Ag nanoparticles are used as a photothermal material. Given the long-term utilization of Ag nanoparticles, they have been coated with a SiO2 layer. Moreover, SiO2 can act as a "reduced reflection" layer that can minimize light reflection on a single Ag nanoparticle, and enhance the nanoparticles' absorbing ability of optical waves. Furthermore, the performance of the evaporator is significantly improved by the addition of cuttlefish powder material in the hydrogel. Specifically, under 1 KW m- 2, the surface temperature of the evaporator reached 41 celcius, the steam generation rate was 1.78 (kg m- 2h-1), and the solar thermal conversion efficiency is 94 %. Moreover, when the evaporator is used in heavy metal sorption, the resulting evaporated water meets international drinking water criteria. After photothermal evaporation, the ion concentrations of Cu, Mn and Cd decreased from 1000, 100 and 20 mg L-1 to 0.021, 0.017 and 0.04 mg L-1 respectively. This study provides a feasible idea for the practical application of photothermal evaporator.