Salt-resistant Schiff base cross-linked superelastic photothermal cellulose aerogels for long-term seawater desalination

Abstract

Solar steam generators (SSGs) that continuously supply clean water resources under solar radiation have been recognized as a sustainable approach to mitigate the global water and energy crisis. However, most SSGs currently face the accumulation of salt on the surface during long-term seawater desalination, which hinders the water supply and vapor escape and significantly reduces the evaporation efficiency. Inspired by the porous water channels of reverse transportation, the SSG (PPy@PEI@A-CNF aerogel) with superelastic and photothermal properties was obtained by the Schiff base reaction of aldehyde-based cellulose nanofibers (A-CNF) and polyethyleneimine (PEI) and freeze assembly, and further in-situ polymerized with polypyrrole (PPy). This aerogel with porous hierarchical structure performed outstanding mechanical robustness (89.9% strain remaining after 100 compress-release cycles), ultra-low density (0.021 g cm−3) and thermal conductivity (0.042 W m−1 K−1), high porosity (97.72%) and full spectrum solar energy absorption (98.4%). Moreover, the aerogel could be used for solar-driven water evaporation, and its evaporation rate and efficiency were as high as 1.66 kg m–2h−1 and 94.62% under 1.0 sun. Owing to the rapid re-dissolution of the salt in the reverse transport of macroporous structure, the aerogel exhibited excellent salt-resistant and self-desalting properties during long-term seawater desalination, and also showed superior purification effects and reusability. These findings provide a new method for designing reusable macroporous SSGs to meet eco-friendly, efficient and sustainable fresh water access.