Recyclable physical hydrogels as durable and efficient solar-driven evaporators

Solar-driven hydrogel evaporator has drawn considerable attention due to its promising applications in desalination and sewage treatment. However, it remains a critical challenge to establish hydrogel-based photothermal materials in a facile, efficient, and recyclable way. In this work, we develop a recyclable, durable, and efficient hydrogel evaporator with excellent evaporation performance by simple integration of poly (N-acryloyl glycinamide) PNAGA, chitosan, and carbon nanotubes (CNTs). The physical composite hydrogel displays extremely high solar absorbance of 97.2 % covering the wavelength from 250 to 2500 nm and shows exceptional solar-vapor conversion efficiency of 92.0 % as well as a high steam generation rate of 2.42 kg m−2 h−1 under one sun irradiation. Strong tolerance of bacteria growth, salt, acid, and alkali environments simultaneously emerges in the gel because of the presence of –NH2 functional groups in chitosan chains, making it ideally suitable for the desalination of seawater. By making use of the reversible sol-gel transition of PNAGA, the hydrogel evaporator can be recycled using a simple melt-cooling method. The recycled gel possesses barely deteriorated steam generation performance compared with the original one. This work shapes an environmental-friendly and low-cost hydrogel evaporator in a facile and recyclable way, which provides a simple method for the efficient collection of freshwater resources.