MXene-decorated carbonized MOF nanofluids with hybrid ionic liquids for enhanced solar-thermal conversion

Recently, with the escalating severity of energy consumption issues, solar energy has attracted significant attention due to its clean, pollution-free, and renewable characteristics, among which solar thermal utilization is currently the most efficient way of utilizing solar energy. Ionic liquids (ILs) exhibit excellent thermal stability and wide liquid-phase range, but their limited optical absorption properties restrict practical applications. In this work, we pioneer the incorporation of magnetic ionic liquids (MILs) into nanofluids (NF) to boost the solar-thermal conversion of ILs-based systems. A novel nanofluid was engineered through electrostatic assembly of C-MOF@Ti₃C₂T_x with hybrid ionic liquids (HIL), where HIL was synthesized by integrating MIL into non-magnetic ILs to enhance the optical absorption of the base fluid. Moreover, MXene deposition on the C-MOF surface after copper oxide removal effectively reduces the interfacial reflection coefficient of nanoparticles while improving full-spectrum solar absorption. The research indicates that incorporation MIL significantly enhances the optical absorption properties of the base fluid. The C-MOF@Ti₃C₂T_x-HIL NF exhibits excellent thermal stability below 400 °C, low viscosity (50 mPa·s at 25 °C), and high solar absorption capacity, making it highly suitable for both pumping and heat generation in industrial applications. Furthermore, stagnation temperature tests revealed that the C-MOF@Ti₃C₂T_x-HIL nanofluid achieves full-spectrum absorption at an ultralow mass fraction of 0.02 wt%, demonstrating rapid heat generation kinetics. The system attained an equilibrium temperature of 79.0 °C with a peak solar-thermal conversion efficiency of 91.2 % under 1 Sun irradiation. Additionally, the material exhibits exceptional cycling stability and water evaporation performance, showing promising application potential for seawater desalination and biomedical fields.