CNT-based gel-coated cotton fabrics for constructing symmetrical evaporator with up/down inversion property for efficient continuous solar desalination

Solar-driven seawater desalination has drawn much attention, while the practical application has been limited by the unsatisfactory photoabsorption as well as solid-salt crystallization. To address the issues, hereby we have constructed a symmetrical evaporator with up/down inversion property by using carbon nanotubes (CNTs)-based gel-coated cotton fabrics. Such CNT-cotton fabrics have porous structure and strong photoabsorption in 280–2500 nm range. Subsequently, two CNT-cotton fabrics are coated on cotton-embedded polystyrene for constructing symmetrical evaporator. Such symmetrical evaporator is placed in NaCl solution (3.5 wt%), it exhibits an excellent evaporation rate of 1.62 kg m−2 h−1 under 1 sun irradiation. To investigate the effects of solid-salt crystallization, a higher concentration of NaCl solution (21 wt%) can be used for evaporation. As expected, the evaporation rate decreases from 1.62 to 0.75 kg m−2 h−1 in 8 h because of solid-salt crystallization on the upper-surface. Importantly, the symmetrical evaporator can eliminate adverse effect of solid-salt crystallization by using an inverse strategy (twice an hour), remaining a stable evaporation rate (1.49–1.62 kg m−2 h−1) during long-time test. Therefore, the present design of CNT-cotton fabrics and symmetrical evaporator may provide some new insights for efficient continuous desalination under sunlight irradiation.