A design of bifunctional photothermal layer on polysulfone membrane with enclosed cellular-like structure for efficient solar steam generation.

• As high as 124.14% of evaporation efficiency was achieved by 2D photothermal membrane. • The PSf substrate possessed ultra-low thermal conductivity of 0.04 W m−1 K−1. • The CB/rGO/PS layer provided dual-function including light absorption and water path. • The introduction of rough structure enhanced light absorption to 96.25%. Solar steam generation was widely considered as a promising desalination method due to its pollution-free, coordination and sustainability. In the present work, we proposed a new fabrication strategy for photothermal composite membrane, which was composed of hydrophobic polysulfone (PSf) membrane substrate and top hydrophilic functional layer involved reduced graphene oxide (rGO) and polystyrene (PS) microspheres. The PSf membrane obtained via the solvent volatilization process had ultra-low thermal conductivity by virtue of the enclosed cellular-like pore structure, which effectively restrained the heat diffusion from the absorption surface to the bottom water and ensured that the heat energy was confined to the evaporation surface. The rGO/PS layer acquired by introducing PS microspheres into the light absorbing layer showed high broadband solar absorption capacity depending on multiple scattering effects, and also provided efficient and continuous water transportation path by right of strong capillarity. Finally, the rGO/PS@PSf composite membrane showed excellent solar water evaporation rate of 1.06 kg m−2h−1 and evaporation efficiency of 69.58% under one sunlight. Further, with the addition of carbon black (CB) into rGO/PS functional layer and breaking the membrane into several pieces, the solar evaporation rate and efficiency had been further improved up to 1.86 kg m−2h−1 and 124.14%, respectively. This composite structure makes it a promising material for efficient seawater desalination. [ABSTRACT FROM AUTHOR]