Interlayer Architecture Modulates Water State and Transport in Chitosan Aerogels for Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation offers a sustainable route to freshwater production, yet the role of evaporator microstructure in regulating water state and transport remains insufficiently understood. Here, chitosan-based photothermal aerogels with tunable lamellar architectures were fabricated by freeze-drying, using carbon nanotubes as broadband solar absorbers. Varying the chitosan concentration modulated the interlayer spacing and associated water state within the aerogels. The optimized CS2.5 aerogel exhibited the highest intermediate-water proportion and the lowest apparent evaporation enthalpy of 1652.1 kJ kg−1, while maintaining solar absorptance above 97.8%. Under 1 sun irradiation, CS2.5 achieved an evaporation rate of 2.33 kg m−2 h−1 and maintained stable performance in NaCl solutions of up to 15 wt%, organic-contaminated water, and prolonged cycling tests. Idealized COMSOL Multiphysics 6.3 simulations indicated that a moderate interlayer spacing promoted a uniform velocity distribution and smooth pressure gradient, thereby facilitating water transport. During six consecutive days of outdoor operation, the evaporator delivered daily evaporation yields of 1.38–2.30 kg m−2 under fluctuating environmental conditions. These findings provide insights into coordinating lamellar architecture, water-state regulation, and fluid transport for efficient solar evaporation.