Janus biocomposite aerogels constituted of cellulose nanofibrils and MXenes for application as single-module solar-driven interfacial evaporators

Abstract

Novel biocomposite aerogels with Janus character are fabricated for application as interfacial evaporators, using cellulose nanofibrils (CNFs) as building blocks and Ti₃C₂T_x MXenes as functional fillers via pre-freezing, solvent exchange, unidirectional freeze-casting, and freeze-drying. The upper and lower parts of the Janus CNF/MXene composite aerogels (JCM aerogels) exhibit opposite wettabilities and perform complementary functions. The lower part of the aerogel is a hydrophilic CNF aerogel for enabling continuous upward water transport. The function of the upper part, a silane-modified hydrophobic CNF/MXene aerogel, is photothermal conversion and heat insulation for efficient evaporation of water. The JCM aerogels self-float stably on the water surface and achieve a high evaporation rate of 2.287 kg m⁻² h⁻¹ at an efficiency of 88.2% under 1 sun illumination. Numerical simulations for heat and mass transfer confirm the synergy between the two parts of the composites, which enabled the excellent evaporation performance observed. In addition, the JCM aerogels showed excellent salt resistance and seawater durability in simulated solar-driven desalination experiments. The design of these interfacial evaporators may offer new insights for developing reliable and environmentally friendly water purification technologies.