Nanocellulose hydrogel interface for dual-function solar evaporation and industrial black liquor treatment

Solar-driven interfacial evaporation offers a sustainable approach to freshwater production via localized photothermal conversion, but challenges, including salt crystallization that hinders evaporation and relatively low evaporation efficiency, still remain. To address these limitations, a novel PCR hydrogel made of poly (vinyl alcohol) (PVA), cellulose nanocrystals (CNC), and reduced graphene oxide (RGO) was developed. The PVA/CNC framework constructs densely cross-linked pores and introduces hydrophilic functional groups, which effectively balance salt resistance and water supply, and the inclusion of RGO endows the evaporator with broad spectral absorption (250-2500 nm) and a high average light absorption of 95%. Notably, the presence of hydrophilic groups within the polymer network reduces the evaporation enthalpy of water, resulting in an evaporation rate of 1.83 kg m^-2 h^-1 using 3.5 wt% NaCl solution under 1 sun irradiation (1 kW m^-2). From the perspective of industrial application, the hydrogel also purified black liquor from pulp mill at an evaporation rate of 1.88 kg m^-2 h^-1. Such a composite hydrogel exhibits a high evaporation rate under elevated salt concentrations and industrial wastewater conditions while exhibiting exceptional fatigue resistance, offering a sustainable pathway for desalination of high-salinity seawater and purification of industrial wastewater.