Effective solar-driven evaporators with urchin-like CuO particles and directional polyvinylidene fluoride scaffolds via directional dimethyl sulfoxide crystallization and non-solvent induced phase separation

Abstract

Solar-driven evaporators with vertical channels usually exhibit excellent desalination due to the fast water transportation and excellent salt tolerance, which are often fabricated via a directional liquid nitrogen-assisted ice templating method and freeze-drying process. However, they are reliant on a very limited number of water-soluble polymers and hydrophilic inorganic materials, and the freeze-drying process costs a long time and much energy. A highly efficient and straightforward process for the fabrication of solar-driven evaporators with directional channels from water-insoluble materials is urgent. Here, water-insoluble polyvinylidene fluoride was dissolved in dimethyl sulfoxide (DMSO), and then the solution was engineered to PVDF scaffolds by the combination of directional DMSO crystallization with the commonly porous membrane formation method of non-solvent (water) induced phase separation. The result is the creation of oriented perpendicular pores to the surfaces and framberry-like microparticles on the pore walls. After the in situ deposition of urchin-like CuO particles with high solar adsorption on PVDF scaffolds, PVDF/CuO solar-driven evaporators have been successfully constructed. The evaporate rate depends on the PVDF content and CuO loading. Briefly, PVDF/CuO evaporators fabricated from high PVDF content of more than 3 wt% have low porosity, slow water supply, and poor hydrophilicity, resulting in a low evaporate rate and high evaporation enthalpy. The optimized 3D PVDF/CuO evaporator (V3-9 h) with a PVDF content of 3 wt% and CuO loading of 31.3 ± 1.6 wt% has a high pure water evaporation rate of 3.2 ± 0.2 and 3.5 ± 0.3 kg m-2h−1 under sun illumination at 1 and 2 kW m−2, respectively. And the evaporation enthalpy is as low as 1083.8 ± 25.5 J/g, 55 % lower than pure water. Moreover, the sample exhibits a similar evaporation rate in 3.5 wt% NaCl solution because the verticle channels endow the evaporator with excellent salt tolerance. The facile and scalable fabrication process of solar-driven evaporators with directional channels will greatly boost the development of cost-effective desalination.