Single-Component TiO₂Tubular Microengines with Motion Controlled by Light-Induced Bubbles

Abstract

In this work, light-controlled bubble-propelled single-component metal oxide tubular microengines have for the first time been demonstrated. For such a simple single-component TiO2 tubular microengine in H2O2 aqueous solution under UV irradiation, when the inner diameter and length of the tube are regulated, the O2 molecules will nucleate and grow into bubbles preferentially on the inner concave surface rather than on the outer surface, resulting in a vital propulsion of the microengine. More importantly, the motion state and speed can be modulated reversibly, fast (the response time is less than 0.2 s) and wirelessly by adjusting UV irradiation. Consequently, the as-developed TiO2 tubular microengine promises potential challenged applications related to photocatalysis, such as "on-the-fly" photocatalytic degradation of organic pollutes and photocatalytic inactivation of bacteria due to the low cost, single component, and simple structure, as well as the facile fabrication in a large-scale.

Light‐Induced Motion of Microengines Based on Microarrays of TiO2 Nanotubes

“…generated by the UV irradiation at the surface of the microarray of TiO 2 nanotubes. Under UV exposure, the following reactions are possible on the surface of TiO 2 …”

“…The second mechanism is related to bubble generation due to the photocatalytic decomposition of hydrogen peroxide, stimulated by the electron–hole pairs created under the UV irradiation (especially prominent in the anatase and rutile structures) . This effect occurs when the electromagnetic energy quantum exceeds 3.0 eV in case of rutile and 3.2 eV in case of anatase [ Figure and Video S1, Supporting Information].…”

“…Bubble generation is also possible at the outer surface of the tubes, where different structural defects (especially prominent for samples annealed at high temperatures) act as nucleation points. However, the absence of confined spaces generally leads to diffusion and reabsorption of the generated oxygen molecules in the solution, resulting in no bubble formation . Only in the case of relatively big structures, the formation and accumulation of bubbles around a microarray occurs, which are finally bulked into one single bubble that surrounds the microarray (Figure b).…”

“…TiO 2 has been implemented as a potential photoactive structure by using strain‐engineering technology to obtain rolled‐up microtubes or integrated as an outer layer in the TiO 2 /Au/Mg self‐propelled microspheres representing future platforms for green degradation of pollutants. Tubular micrometer‐scale TiO 2 structures, which have been recently synthesized by using an alternative dry spinning method, move in the presence of hydrogen peroxide (H 2 O 2 ) . Another promising approach, namely electrochemical anodization of titanium, allows for fabrication of highly ordered arrays of TiO 2 nanotubes bound in micromembranes, which can act as a bunch of nanomotors, thus bringing a novel nanostructured material into play.…”

Recent Progress on Bioinspired Self‐Propelled Micro/Nanomotors via Controlled Molecular Self‐Assembly

“…Particularly, light is one of the most powerful and versatile physical stimuli used to regulate the propulsion of synthetic motors in fluids at the micro/nanoscale . For instance, Guan and co‐workers reports the UV light‐induced “on/off” movement of single‐component TiO 2 tubular microengines in H 2 O 2 solution . Palacci et al describes chemically powered photoactivated colloidal micromotors and their dynamic assembly and disassembly under blue light irradiation .…”