Constructing a solar evaporator by stacking exhausted wood sponges for freshwater generation and fertilizer recovery

Solar water evaporation is an efficient and sustainable technology. To further reduce energy consumption and improve cost efficiency, the surface modification of wood sponge by polypyrrole-glutathione (PGWS) was achieved using an in-situ synthetic method. The PGWS exhibits excellent adsorption efficiency for Hg(II) ions with adsorption capacity of 330.8 mg g-1 at 25 °C. Following Hg(II) absorption, the PGWS could be upcycled for solar steam generation. A stackable device was constructed by stacking wood sponge under the Hg(II) saturated PGWS (PGWS-Hg(II)), which showed the highest water evaporation rate of 2.14 kg m-2 h-1 under 1 kW m-2. Moreover, collecting paper was inserted between the stacked PGWS-Hg(II) and wood sponge for the collection of salts. The salt can be successfully collected from the simulated fertilizer plant effluent and then used as a nutrient for growing plants using a hydroponic system. The facile design of stackable evaporation provides an opportunity for wastewater utilization by harvesting solar energy.