Vertically symmetrical evaporator based on photothermal fabrics for efficient continuous desalination through inversion strategy

Solar-driven interfacial evaporation is an attractive method for seawater desalination, but the solid-salt crystallization on solar-absorber severely shelters sunlight and thus deteriorates the evaporation rate. To solve this problem, herein we have reported vertically symmetrical evaporator based on cotton-CsxWO3 fabrics. CsxWO3 nanorods have been prepared and then coated on cotton fabrics. The resulting cotton-CsxWO3 fabrics exhibit broad UV-Vis-NIR photoabsorption from 200 to 2500 nm with solar absorbance efficiency of 90.5%. Subsequently, by coating two similar cotton-CsxWO3 fabrics on double surfaces of a cotton-embedded polystyrene (PS) foam, vertically symmetrical evaporator has been designed and constructed. When the evaporator is floating on NaCl solution (3.5 wt%), cotton-CsxWO3 fabric on top surface can absorb light under solar irradiation (1.0 kW m−2), conferring a high evaporation rate of 1.56 kg m−2 h−1 with an efficiency of 86.8%. When high-concentration (21 wt%) NaCl solution is used, the evaporation rate goes down from 1.52 to 0.53 kg m−2 h−1 within 8 h, due to the solid-salt crystallization on top surface. Importantly, the symmetrical evaporator can be self-cleaned by an inversion strategy (2 times h−1), conferring high and stable rate (1.53–1.58 kg m−2 h−1) in the 20-h cycling evaporation and thus having great potential in the practical seawater desalination.