Facile Fabrication of Ultralow Density and Ultrahigh Solar Absorption Monolithic Phenolic Carbon Aerogel from Lignite for Solar Vapor Generation

Solar vapor generation has been recognized as one of the most sustainable desalination methods due to its high energy efficiency and zero carbon emissions. However, it is often limited by poor mechanical properties, a complex preparation process, and/or the high density of photothermal materials. Here, we present a simple and effective method for preparing high-strength lignite-based phenolic carbon aerogels (LPCAs) for seawater desalination. LPCAs were prepared using an ethanol-soluble portion (ESP) from lignite as the raw material and melamine as the skeleton by polymerization/gelation, vacuum-drying, and carbonization, avoiding the energy-intensive freeze-drying step. Due to the abundant alkyl side chains and condensed aromatics in the ESP, LPCA has an ultralow density (42 mg·cm–3) and ultrahigh light absorbance (97.3%) without the need of additional expensive photothermal materials. Moreover, LPCA can regulate the intermediate water content and absorb energy from the environment. Based on these advantages, the evaporation rate of the LPCA evaporator can reach up to 2.40 kg·m–2·h–1 under 1 sun with an energy efficiency of 93.5%. Additionally, LPCAs with high strength (4.48 MPa under 90% strain), self-floating, good salt resistance, and applicability under harsh conditions facilitate practical application for producing clean water.