Structure Architecting for Salt‐Rejecting Solar Interfacial Desalination to Achieve High‐Performance Evaporation With In Situ Energy Generation

Abstract

requirement has given rise to research thrusts being focused on the development of solar-driven evaporation based desalination technologies. [4][5][6][7] The research on using solar energy in the desalination process has a long history. [3,8,9] In a traditional singleslope basin-like solar still (Figure 1a), saline water is heated and subsequently evaporated by directly exposing to solar radiation. Solar energy is absorbed and converted into thermal energy by a black light-absorbing liner that is situated at the bottom of the solar basin. [10] Due to this design, the solar absorber is immersed in bulk seawater and it hardly receives a fraction of the incoming solar radiation owing to poor light penetration through the thick water layer. Furthermore, the produced heat is easily dissipated into the bulk water, and further lost to the surroundings through water surface radiation, convection and conduction. Due to the above reasons, the resulting solar-tosteam conversion efficiency is inevitably low. Nanoparticle dispersed fluid was then demonstrated to harness solar energy and found to be a great boon to direct water vapor generation. [11,12] A solar conversion efficiency of up to ≈70% can be possibly achieved because heat loss to bulk water is mitigated ( Figure 1b). [13,14] However, research on this advancement didn't last because of the development of solar interfacial heating strategy, which is shown in Figure 1c. The concept of interfacial evaporation was first put forth in 2014 by two reports simultaneously, [15,16] and received a surge of attention and interest immediately in the following years. The most prominent feature of solar interfacial evaporation lies in the position of the solar absorber, which is at the interface between saline liquid and the above air. This special configuration not only minimizes heat loss from the solar absorber to bulk water, but also provides significantly more surface area for prompt vapor release. Also, solar radiation is photothermally localized at the surface of solar absorber, giving rise to high surface temperature, which enables fast heat transfer to water. With it, water transported from reservoir can be heated and evaporated immediately to achieve a higher rate of steam generation. In addition to the differences in heating strategies, it should be noted that all the solar stills follow the same evaporation-condensation route for desalination and clean water collection, and to this end, a similar device structure (e.g., solar still with sloping cover) is usually employed.The past few years have witnessed a rapid development of solar-driven interfacial evaporation, a promising technology for low-cost water desalination. As of today, solar-to-steam conversion efficiencies close to 100% or even beyond the limit are becoming increasingly achievable in virtue of unique photothermal materials and structures. Herein, the cutting-edge approaches are summarized, and their mechanisms for photothermal structure architecting are uncovered in order to achieve ultrahigh conversion e...

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