Nitrogen-doped graphene quantum dots hydrogels for highly efficient solar steam generation

Solar evaporation is a sustainable and green strategy to relieve the growing global freshwater crisis. In this strategy, a solar irradiation absorber platform absorbs the sunlight and converts it into heat for water evaporation. Herein, a new class of nitrogen-doped graphene quantum dots (N-GQDs) hydrogels has been developed for highly efficient solar water evaporation via the heat localization mechanism. N-GQDs hydrogels are fabricated via the hydrothermal self-assembly process. Using N-GQDs with different lateral size ranges as the precursor, hydrogels with different structural properties and solar water evaporation efficiencies are prepared. The highest achieved solar steam generation efficiency in this work is 89.7% obtained by employing N-GQDs with the smallest lateral size range in the precursor solution. The steam generation efficiency of hydrogels reduces with increasing the lateral size of synthesized N-GQDs in precursors. The colloidal morphology, high hydrophilicity, hierarchical pore structure, and low thermal conductivity of prepared N-GQDs hydrogels result in the high performance of these structures in solar water evaporation applications.