Polyaniline-modified MXene oil-based nanofluids with excellent high-temperature stability for efficient solar thermal harvesting.

Oil-based MXene nanofluids exhibit significant promise for direct absorption solar collectors due to their broadband light absorption. However, poor high-temperature stability limits their practical use. Here, we present an effective strategy to stabilize MXene nanofluids by modifying them with polyaniline (PANI). This approach involves the in situ polymerization growth of PANI on crumpled Ti3C2Tx nanosheets, followed by grafting with oleylamine (OAm). Importantly, we optimized the PANI layer thickness to create a robust steric-repulsion barrier via covalent interfacial bonds, effectively counteracting strong van der Waals forces. Additionally, the crumpled morphology and hydrophobic grafted OAm collectively minimize interparticle attraction. As a result, the modified MXene nanofluids maintained a homogeneous dispersion after heating to 280 °C for 24 h and during thermal aging at 200 °C for 14 days. Moreover, during photothermal cycling tests at 20-sun irradiance with fluid disturbance, the nanofluid reached a peak temperature of 260 °C without significant degradation. Notably, the nanofluids not only showed enhanced stability but also retained high photothermal conversion efficiency, achieving 88.5% at 100 ppm. This work offers a new perspective on overcoming the bottleneck to using nanofluids in practical applications.