Janus Poly(ionic liquid) Monolithic Photothermal Materials with Superior Salt-Rejection for Efficient Solar Steam Generation

The development of photothermal materials with high light-to-heat conversion efficiency as well as superior salt-resistant performance is of importance for real solar desalination. Here, we demonstrate a strategy for facile fabrication of Janus photothermal materials based on porously superhydrophilic poly(ionic liquid) monolith coated with strong hydrophobic carbon soot (C-PDVB-BF4ILs) for high-efficiency solar steam generation. Based on their mesoporous three-dimensional architecture, excellent light absorption (92%), and low thermal conductivity (0.293 W m–1 K–1), the evaporation conversion efficiency of C-PDVB-BF4ILs reaches up to 92.4% under 1 sun illumination without additional thermal insulators being used, which is comparable to the best performance of the current reported bilayered evaporation systems. More interestingly, by applying it for solar evaporation in saline solutions, the Donnan exclusion effect generated from imidazolium-based cations of poly(ionic liquid) against cations from saline solution endows the C-PDVB-BF4ILs excellent salt-resistant performance, by combination with its unique Janus structure. Based on its simple and scalable fabrication process with high energy conversion efficiency and excellent salt resistance, the strategy proposed in this work may be expected to provide new possibilities for the rational design and fabrication of high-performance photothermal conversion materials for real solar desalination applications.