Electrospinning-based architectural engineering of multi-layered fibrous membranes with spatially defined wettability for solar desalination.

Solar-driven interfacial evaporation has been widely studied for seawater desalination and wastewater treatment. However, it is still difficult to achieve efficient heat localization and continuous water transport in a single evaporator. In this work, a PAN-PS-PAN sandwich-structured photothermal evaporator was fabricated by sequential electrospinning using a dual-channel needle assembly. The evaporator consisted of polyacrylonitrile-polystyrene-polyacrylonitrile (PAN-PS-PAN, PPPS) layers. Carbon nanoparticles (C NPs) were incorporated into both PAN and PS precursor solutions, with a higher nominal C NP fraction in the PAN-based precursor. The PAN-rich outer layers remained strongly hydrophilic and supported water redistribution toward the evaporation interface, whereas the PS-rich middle layer remained hydrophobic and served as the principal internal thermal barrier. Therefore, the PAN-PS-PAN structure enabled continuous water supply while retaining most heat near the evaporation interface. Owing to this structural design, the PPPS evaporator showed improved water supply and heat utilization. Under one-sun irradiation, the evaporation rate reached 1.33 kg m-2 h-1, and the solar-to-vapor conversion efficiency was 90.5%. The evaporator also showed good purification ability for organic dye solutions, acidic and alkaline water, Tween 80/kerosene emulsion, and PEG aqueous solutions with different concentrations. These results demonstrate the potential of the PPPS evaporator for solar-driven seawater desalination and complex wastewater purification.