Electro-assisted alignment of coir fiber cellulose aerogel with low tortuosity channels for solar steam generation

Biomass-derived substrates have high porosities and hydrophilic properties that match the requirements as substrate in a heat localization solar steam generation (SSG) system. Nevertheless, the irregular branched pattern of the pore structure hinders water flow from bottom to top to immediately replace the evaporating water. Here we report a method to align fiber orientation of cellulose aerogel derived from coir fiber by an electro-assisted method. Specifically, an electric field was applied during the initial phase of gelation process during cellulose aerogel preparation using the dissolution-coagulation route. The vertically aligned fibers in the electro-assisted cellulose aerogel result in higher thermal conductivity (0.246 W m-1 K-1) due to a shorter path of solid for heat flow, smaller thermal tortuosity, than that of the unaligned fibers (0.011 W m-1 K-1). Moreover, they also provide a shorter path of water flow, which is indicated by the higher hydraulic conductivity and the higher water pumping capacity. When used as the substrate for bilayer heat localization SSG system by depositing magnetite nanoparticles as the photothermal material, the vertical and unidirectional fibers can quickly replace the evaporating water resulting in high solar evaporation rate of 1.178 Kg m-2 h-1 under 1 sun irradiation. The electro-assisted cellulose aerogel appears promising as a sustainable and excellent substrate for bilayer SSG system in solar-driven water purification to supply clean water from seawater.