Laser-induced photothermal generation of flexible and salt-resistant monolithic bilayer membranes for efficient solar desalination

Harvesting solar energy and generating steam through solar thermal energy are viable approaches with diverse applications such as power generation, desalination, and water purification. Particularly, for efficient and stable solar desalination, hierarchically porous materials are desired to enable the required multiple functionalities. However, high thermal/chemical energy required and time consumed remain roadblocks. In this study, a facile, fast, and scalable laser-induced photothermal method to achieve flexible monolithic bilayer sheets (MBS) of hierarchically porous graphitic carbon (HPGC) and polymeric foam for use in salt-resistant and flexible solar steam generators is reported. The MBS-based self-floating solar steam generator shows outstanding solar desalination performance with a solar thermal efficiency of 83.2% (1-sun) and a high salt-rejection ratio (99.9%). Efficient solar thermal energy transformation is achieved by the versatile multi-functionalities of the MBS, including broad-spectrum solar light absorption, heat localization, and capillary action. Anisotropic wetting properties of hydrophobic HPGC and hydrophilic polyimide (PI) foam effectively prevent salt accumulation on the HPGC surface. The salt-resistant MBS enable long-term stability for solar desalination with actual seawater. Our laser-based photothermal method has potential in the development of high-performance solar thermal systems with substantial cost reduction by scalable production of multiscale hierarchically structured materials from micro-structured polymers.