Light-Driven Au-WO₃@C Janus Micromotors for Rapid Photodegradation of Dye Pollutants

A novel light-driven Au-WO₃@C Janus micromotor based on colloidal carbon WO₃ nanoparticle composite spheres (WO₃@C) prepared by one-step hydrothermal treatment is described. The Janus micromotors can move in aqueous media at a speed of 16 μm/s under 40 mW/cm² UV light due to diffusiophoretic effects. The propulsion of such Au-WO₃@C Janus micromotors (diameter ∼ 1.0 μm) can be generated by UV light in pure water without any external chemical fuels and readily modulated by light intensity. After depositing a paramagnetic Ni layer between the Au layer and WO₃, the motion direction of the micromotor can be precisely controlled by an external magnetic field. Such magnetic micromotors not only facilitate recycling of motors but also promise more possibility of practical applications in the future. Moreover, the Au-WO₃@C Janus micromotors show high sensitivity toward extremely low concentrations of sodium-2,6-dichloroindophenol (DCIP) and Rhodamine B (RhB). The moving speed of motors can be significantly accelerated to 26 and 29 μm/s in 5 × 10^-4 wt % DCIP and 5 × 10^-7 wt % RhB aqueous solutions, respectively, due to the enhanced diffusiophoretic effect, which results from the rapid photocatalytic degradation of DCIP and RhB by WO₃. This photocatalytic acceleration of the Au-WO₃@C Janus micromotors confirms the self-diffusiophoretic mechanism and opens an opportunity to tune the motility of the motors. This work also offers the light-driven micromotors a considerable potential for detection and rapid photodegradation of dye pollutants in water.