3D-Printed Liquid Metal-in-Hydrogel Solar Evaporator: Merging Spectrum-Manipulated Micro-Nano Architecture and Surface Engineering for Solar Desalination

Solar desalination driven by interfacial heating is considered a promising technique to alleviate the freshwater shortage crisis. However, its further extension and application are confined by factors such as highlighted salt accumulation, inferior energy efficiency, and poor durability. Herein, a microsized eutectic gallium-indium (EGaIn) core-shell nanodroplet (denoted as LMTE) with photo-cross-linking and photothermal traits, stabilized by allyl glycidyl ether (AGE)-grafting tannic acid (TA), is explored as the solar absorber for broadband light absorbing and localized micro-nano heat channeling. The LMTE nanodroplets are formulated directly with highly hydrated polymers and photosensitive species to successfully develop a water-based photothermal ink suitable for digital light processing (DLP) 3D printing. As a demonstration, the LMTE composite hydrogel-forged milli-conical needle arrays with metal-phenolic network (MPN)-engineered wettability and photothermal enhancement can be printed by the digital light processing (DLP) technique and designed rationally via a bottom-up strategy. The 3D-printing hydrogel evaporator is composed of spectrum-tailored EGaIn nanodroplets for efficient photon harvesting and MPN-coated milli-cone arrays for water supplying with micro-nano channeling, which function cooperatively to bestow the 3D solar evaporator with superior solar-powered water evaporation (2.96 kg m^-2 h^-1, 96.93% energy efficiency) and excellent solar desalination (salt cycle and site-specific salt crystallization). Furthermore, a robust steam generating/collecting system of the 3D solar evaporator is demonstrated, providing valuable guidance for building a water-energy-agriculture nexus.