Self-dispersion and steric hindrance co-stabilized oil-based MXene nanofluids for efficient medium to high temperature photothermal conversion

MXene-based nanofluids exhibit outstanding broadband solar absorption capabilities in direct absorption solar collectors (DASCs); however, nanoparticle aggregation at elevated temperatures poses challenges to their practical use. To address this limitation, we develop a dual-stabilization strategy for oil-based MXene nanofluids that combines self-dispersion and steric hindrance mechanisms. This innovative approach employs hydrazine hydrate intercalation (reducing particle size) with freeze-drying-induced surface crumpling to enhance the intrinsic self-dispersion capability of MXene. Concurrently, long-chain oleylamine ligands create spatial barriers that prevent direct contact between nanoparticles. This integrated approach effectively mitigates MXene aggregation driven by van der Waals forces, as evidenced by a mere 0.14 % reduction in absorbance (765 nm) after 120 h of thermal aging at 150 °C, while maintaining the initial particle size distribution. Furthermore, the optimized nanofluid demonstrates exceptional photothermal performance, achieving a solar-weighted absorption fraction exceeding 97 % at a concentration of 60 ppm with a 3 cm path length and an equilibrium temperature of 195.6 °C under 6 sun irradiation, 44 % higher than that of the base fluid. Additionally, the system exhibits consistent photothermal stability during cycling, with relative peak temperature fluctuations remaining below 3.1 % under concentrated irradiation (4 sun and 6 sun). These results highlight the nanofluid's excellent optical absorption and thermal stability within the medium to high-temperature range of 100 °C–200 °C, implying that the proposed stabilization methodology is promising for developing durable MXene nanofluids suitable for this operational window in solar thermal applications.