Biomass-Derived Bilayer Aerogels Enabled by Fractionated Lignin Nanoparticles for Sustainable Solar Interfacial Evaporation

Lignin is a sustainable photothermal material for solar interfacial evaporation, but its structural heterogeneity and poor dispersion limit efficient utilization. Here, we develop a biomass-derived bilayer LNP@CCH aerogel evaporator comprising a lignin nanoparticle (LNP)/chitosan photothermal layer and a CNF/Chitosan (CCH) water-transport layer. Fractionation reduces lignin heterogeneity and identifies a fraction with favorable photothermal properties, which is subsequently converted into size-controlled LNPs. The resulting LNP@CCH aerogel evaporator combines broadband solar absorption, low thermal conductivity, interconnected capillary channels, and water-state regulation, enabling efficient light harvesting, heat localization, water transport, and reduced apparent evaporation enthalpy. Under 1 sun irradiation, the optimized evaporator achieves an evaporation rate of 2.31 kg m−2 h−1 and a solar evaporation efficiency of 94.4%. It also exhibits stable saline water evaporation and >99% removal of major ions from real seawater, demonstrating the potential of fractionated lignin for sustainable solar desalination.