Halfa grass assembled double-layered hydrogel evaporator for sunlight-driven steam generation and selective uranium extraction

Fresh drinking water and energy are crucial for the human society to live in a sustainable way, and both of these could be attained from the seawater. Herein, we designed a double-layered hydrogel evaporator (PCG@FCG) by using calcined carbon fiber derived from halfa grass (Desmostachya bipinnata) as a light absorbing photothermal material. The bottom hydrophilic layer composed of chitosan (CS), carboxy methyl cellulose (CMC), and amidoxime-modified chitosan (AOC), which helps in water transport to the upper surface of evaporator. The amidoxime modified chitosan helps in selective binding and recovery of uranium from the seawater. Such a judiciously designed PCG@FCG evaporator shows light absorbance of 96 %, stable evaporation rate of 2.0 kg m−2 h−1, having an outstanding selective uranium recovery of 325 mg g−1 under one sun irradiation. These outcomes result from the inherent structural porosity, enhanced evaporation rate, and selectively designed uranium binding sites. In addition, excellent salt-mitigating ability to promote uninterrupted evaporation, ability to purify the organic-contaminated wastewater/seawater endow the PCG@FCG evaporator with efficient seawater desalination ability and selective adsorption of uranium from the seawater. Overall, this innovatively-designed floating evaporator offers a sustainable approach to utilize the lavish resources in the seawater.