When cellulose nanocrystals meet graphene oxide: Structurally enhanced aerogels for efficient solar steam generation and water purification

Pollution, population growth, and climate change are intensifying global freshwater shortages. Traditional methods of collecting freshwater, such as rainwater harvesting and sewage treatment, have high energy consumption, limiting their implementation in underdeveloped regions. On the other hand, solar-driven seawater evaporation offers a promising solution, purifying water using naturally abundant solar energy. Reduced graphene oxide (rGO) is considered as a strong candidate for this purpose due to its broad spectral absorption. However, its hydrophobicity hinders its direct use in solar steam generators. Here, we report the preparation of a series of cellulose nanocrystal (CNC)-rGO aerogels (CGAs) through a one-pot hydrothermal gelation process, followed by unidirectional freeze-drying. The introduction of CNCs enhances the hydrophilicity and structural stability of the resulting CGAs. The CGAs also feature uniform and unidirectional channels that promote efficient water transport, as confirmed by scanning electron microscopy (SEM) and X-ray microtomography (XMT). The CGAs have an optimized water evaporation rate of 1.80 kg m(-2) h(-1) under 1 sun irradiation, with 90 % solar-to-vapor energy efficiency. Moreover, durability and seawater desalination tests provide additional evidence for the practicality of CGAs in water purification. It is anticipated the implementation of CGAs will expedite the application of solar steam generators in practical scenarios.