Three‐Phase Emulsion Derived Solar‐Thermal Reduced Graphene Oxide/Octadecane Phase‐Change Foam for Salt‐Resistant Day‐Night Water Evaporation

Abstract A solar‐thermal reduced graphene oxide/octadecane (RGO/oct) phase‐change foam is fabricated by the interfacial assembly of an air‐in‐oil‐in‐water three‐phase emulsion and subsequent chemical reduction of graphene oxide (GO) for day‐night evaporation and desalination. The GO sheets assemble at the water‐oct interfaces in the presence of an amphiphilic alkyl glycoside while air pores are generated inside the hydrophobic oct component under stirring, leading to GO/oct/air microspheres. During subsequent molding, the GO is chemically reduced with ascorbic acid, and the resultant RGO/oct/air microspheres with closed pores constitute the solar‐thermal RGO/oct phase‐change foam. The air pores suppress heat conduction to bulk water, while the phase‐change oct prevents heat loss to the environment, hence enhancing the heat localization capability of the RGO/oct foam. The foam exhibits a high evaporation rate of 4.29 kg m ⁻² h ⁻¹ under 1‐sun irradiation. Interestingly, oct can release latent heat in the absence of solar light irradiation, enabling water evaporation at nighttime with an evaporation rate of 2.30 kg m ⁻² h ⁻¹ . The overlap molding of the microspheres allows the rearrangement of salt concentration gradients, exhibiting satisfactory salt resistance of the foam during the stable evaporation of brine with 25 wt.% of NaCl for 10 h.