Gelatin–Cellulose Nanofibril Aerogels Featuring Porous Sidewalls for Durable Solar Desalination

Solar-driven interfacial evaporation represents a promising strategy for sustainable freshwater production. However, its practical application is hindered by poor salt resistance and mechanical instability. Herein, an aerogel evaporator with vertically aligned channels was fabricated through directional freeze-drying, using gelatin/cellulose nanofibrils (CNF) as the porous matrix and carbon nanotubes (CNTs) as the photothermal component. Remarkably, by tuning gelatin/CNF ratios, pore size, distribution and sidewall pores were successfully controlled. These sidewall pores function as interchannel ion exchange units, thus promoting salt ion diffusion. Contrary to conventional understanding, the results demonstrate that larger pore size alone does not guarantee better salt resistance. Instead, an optimal balance between pore size and sidewall pore distribution leads to significantly improved salt resistance and higher evaporation rates. The optimized aerogel exhibits outstanding salt resistance, superior mechanical performance and long-term stability in solar desalination, exhibiting high evaporation rates of 2.25 kg·m–2·h–1 (pure water) and 2.20 kg·m–2·h–1 (3.5 wt % brine) under 1 sun. Furthermore, the aerogel demonstrates remarkable water purification capabilities for both acidic/alkaline wastewater and dye-contaminated solutions. This study reveals the critical role of sidewall pores in vertically aligned aerogel channels, providing special insights for balancing high salt resistance and rapid evaporation in aerogel evaporator design.