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.