Crucial role of an aerophobic substrate in bubble-propelled nanomotor aggregation.

A bubble-propelled autonomous micro/nanomotor (MNM) is a device driven by a catalytic reaction that involves a solid-liquid-gas interface, which in turn is a key factor in achieving effective propulsion. Generally, modifying the liquid phase by adding surfactants can improve propulsion, but it has several disadvantages. It is reported that the rapid separation of bubbles will accelerate the movement of MNMs. Our focus is on methods to drive the motor efficiently by controlling the wettability of the solid phase, accelerating bubble separation without compromising the activity of the catalyst. In this study, different from most of the previous studies on moving MNMs, a static Pt loaded TiO2 nanowire aggregation was utilized as a nanomotor aggregation to investigate the wettability of the solid phase on bubble release. In comparison to an underwater aerophilic solid phase, in which bubbles are strongly held on the surface, the nanomotor's aggregation showed good aerophobicity. In particular, after UV illumination for 30 s, the nanomotor's aggregation became superaerophobic, which significantly promoted the release of O2 bubbles. The results of this study reveal how to modify the detachment behaviour of bubbles by controlling the aerophobic behaviour of solid surfaces of autonomous MNMs in an aqueous medium.

Controlled one-sided growth of Janus TiO2/MnO2 nanomotors.

Designing and building new micro/nanomotors are among the most exciting challenges facing nanotechnology. Considering the expensive equipment and the high cost associated with noble metals, a scalable and reliable fabrication method is desired for the fabrication of Janus particles. In this work, we report on the preparation and characterization of self-propelled micromotors based on Janus TiO2/MnO2 nanoparticles. The Janus micromotor is constructed by growing propulsion material MnO2 nanoflakes in situ on one hemisphere of TiO2 by photoreduction of KMnO4 under aerobic conditions. The MnO2 nanoflakes can catalytically decompose hydrogen peroxide fuel to generate oxygen bubbles, which consequently repel the micromotors forward in the solution. Thus, the Janus TiO2/MnO2 nanoparticle represents a promising material for the preparation of micromotors for various biomedical or environmental applications.