Superwetting photothermal membranes enabled by polyphenol-mediated nanostructured coating with raspberry-like architectures for solar-driven interfacial evaporation

Solar-driven interfacial evaporation, as an emerging solar thermal utilization technology for water production, provides an opportunity for alleviate water-energy nexus. Superwetting membranes, as famous interface materials, combine hierarchical micro-nano architectures and open-porous structures that enable high-efficient solar-driven interfacial evaporation. Herein, the design and synthesis of photothermal membranes with polyphenol-mediated nanostructured coating by integrating the tannic acid (TA)-polyethyleneimine (PEI) complexation and the oxidation-mediated TA-FeII complexation is reported. The assembled TA-PEI/FeII/III coating features hierarchical raspberry-like architectures derived from the TA-PEI nanoconjugates and the oxidized metal-organic hybrid networks with black appearance, which enabled the broaden solar absorption, excellent photothermal conversion and fast water diffusion of the photothermal membranes. Driven by sunlight illumination, the photothermal membranes are capable to achieve evaporation rate of 2.01 kg·m−2·h−1 and solar-to-vapor conversion efficiency of 94.6 %, which competes well with other photothermal membranes. The superposition of TA-PEI/FeII/III coating over open-porous membrane substrates synchronously promoted thermal localization and facilitated water-to-steam generation. The reliable durability and salt resistance of the photothermal membranes are also demonstrated. Furthermore, photothermal membranes enables clean water production from seawater and sewage, demonstrating >99.9 % salt and oil pollutant removal. The universality of the polyphenol-mediated coating strategy offers powerful opportunities to engineer photothermal membranes for water purification application.