In-Situ Preparation of Asymmetric Superwetting Laser-Induced Graphene Janus Membrane on Loofah for Efficient Solar Evaporation

Abstract Laser-induced graphene (LIG), with its low-cost advantage, holds significant potential in the field of solar-driven interfacial evaporation. However, most current LIG-based photothermal materials typically require polymers as precursors, which not only raise concerns about environmental sustainability but also result in membranes that often lack interconnected pore structures and suitable wetting gradients. This limits evaporation efficiency and leads to salt crystallization and deposition. To address these bottlenecks, this study proposes a new strategy for constructing asymmetric superhydrophobic Janus photothermal membranes based on natural loofah. Specifically, the top photothermal superhydrophobic layer was achieved by the laser-induced carbonization of loofah that had undergone flame-retardant treatment to generate LIG, followed by surface chemical modification. The bottom superhydrophilic layer was developed through plasma treatment. The effects of laser processing parameters and modifier concentration on the wettability behavior and photothermal conversion performance of the membrane were systematically investigated. The optimized F13-LIG-Plasma membrane exhibited significant differences in wettability, with a water contact angle (WCA) of up to 152° on the top layer and 0° on the bottom layer. Under standard irradiation conditions of 1000 W/m2, its evaporation rate reaches 1.41 kg m–2 h–1. Benefiting from the synergistic interaction between the wettability of the upper and lower layers, the membrane effectively suppresses salt accumulation at the evaporation interface. Furthermore, the membrane demonstrates excellent purification capabilities for a variety of complex water sources; the treated water quality meets drinking water safety standards. In summary, the developed asymmetric superwetting Janus membrane based on natural loofah exhibits significant technical advantages in the fields of solar-driven interfacial evaporation and water treatment, providing new insights for the design of efficient, green, and salt-resistant solar thermal evaporators.