Tuning the heat−salt−water balance for rapid and scalable solar desalination

The mixed temperature gradient evaporator allows us to accelerate water evaporation at low solar irradiance. However, this novel device still requires a trade-off between heat transfer, water supply, and salt rejection. This paper reports an evaporator that achieves the synchronous management of heat, water, and salt by adjusting the height of the sidewall of the solar absorber. Carbon nanoparticles-coated cotton fiber rod is adopted as the multifunctional solar absorber for sustainable solar desalination. In addition, the water pumped by the solar absorber can be far greater than that required for evaporation, which is sufficient to retain the sustainability of water evaporation. Moreover, both positive and negative temperature gradients are formed between the light-receiving surface and the water-solar absorber interface, implying that the solar absorber is allowed to harvest energy from the sun, environment, and bulk water without experiencing conductive heat loss. As a result, this configuration demonstrates a rapid evaporation rate in both light and darkness (5.04 and 3.55 kg m−2 h−1, respectively) when operating in a 3.5 % (w/w) NaCl solution. More importantly, the evaporation rate remains stable during 5 h of operation in 20 % (w/w) NaCl solution. Furthermore, according to a continuous 9-hour outdoor experiment, the water collected by the evaporator per unit area can satisfy the needs of at least three people.