High-speed NIR light-driven nanomotors prepared via hybridization of TiO₂ and Janus Ag-Ag₂S nanoparticles

Photothermal nanomotors driven by near-infrared (NIR) light emerged as a promising advancement in nanoscale propulsion systems. In this study, a novel type of nanomotor actuated by NIR light was prepared by decorating spherical TiO₂ nanoparticles with Janus Ag-Ag₂S nanoparticles. The motion of these nanomotors is studied using optical microscopy with a dual light source. It is found that they can be actuated with a 700 nm driving light and traverse significant distances relative to their size. Motion analysis reveals that their maximum velocity reaches ~ 20 μm·s⁻¹, or about 100 diameters per second. Statistical analysis of over 400 nanomotor trajectories shows that around 60% of them move at maximum velocities of 6 to 12 μm·s⁻¹. Vacuum ultraviolet velocity map imaging photoemission spectroscopy (VMI-PES) is conducted on isolated TiO₂ and Janus Ag-Ag₂S nanoparticles to elucidate electronic level alignment in the hybrid particle. The findings suggest that photothermal, rather than photocatalytic, effects drive nanomotor activation under NIR light. Additionally, our calculations indicate that the difference in absorption cross-sections between Ag-Ag₂S and TiO₂ components generates a temperature gradient (and consequently a pressure gradient) along the nanomotor, which in turn drives its motion. The local temperature rise near the nanomotors is a result of both photothermal effects within individual nanoparticles and thermal interactions between them.