Cellulose nanofiber-based aerogel with Janus wettability for superior evaporation performance and synergistic photocatalytic activities

Cellulose nanofiber (CNF)-based aerogels have received extensive attention in solar-driven interfacial evaporation for their high porosity and renewability. However, there are challenges of salt accumulation and limited evaporation efficiency caused by network collapse. This study presents a hierarchical CuS-coated CNF/polyvinyl alcohol (PVA) aerogel for solar evaporators. The Janus-structured aerogel features a localized CuS photothermal layer on a hierarchical, interconnected porous CNF/PVA aerogel. This design minimizes heat loss by isolating the photothermal layer from the water. The dendritic structure of CNFs, the inherent porosity and the Janus wettability of the aerogel could facilitate rapid water transport and prevent salt accumulation. The hydratable skeleton of CNFs and PVA could activate the water state. The CuS@CNF/PVA aerogel demonstrates a high evaporation rate of 3.20 kg m^-2 h^-1 with an evaporation efficiency of 98.4 % under 1 sun radiation in water. An evaporation rate of 2.51 kg m^-2 h^-1 is achieved in 20 wt% NaCl solution, positioning the aerogel as a promising material for sustainable desalination applications. Moreover, over 70 % of organic dyes in wastewater could be degraded by photocatalysis of the CuS coating. This work provides an effective approach for developing high-performance solar evaporators with synergistic function of interfacial evaporation and photocatalysis.