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

Abstract

An electrochemical approach for manufacturing light-driven nanostructured titanium dioxide (TiO ) microengines with controlled spatial architecture for improved performance is reported. The microengines based on microscale arrays of TiO nanotubes with variable (50-120 nm) inner diameter show a quasi-ordered arrangement of nanotubes, being the smallest tubular entities for catalytic microengines reported to date. The nanotubes exhibit well defined crystalline phases depending upon the postfabrication annealing conditions that determine the microengines' efficiency. When exposed to UV-light, the microarrays of TiO nanotubes exhibiting conical internal shapes show directed motion in confined space, both in the presence and absence of hydrogen peroxide. In the former case, two different motion patterns related to diffusiophoresis and localized nanobubble generation inside of the tubes due to the photocatalytic decomposition of H O are disclosed. Controlled pick-up, transport, and release of individual and agglomerated particles are demonstrated using the UV light irradiation of microengines. The obtained results show that light-driven microengines based on microarrays of TiO nanotubes represent a promising platform for controlled micro/nanoscale sample transportation in fluids as well as for environmental applications, in particular, for the enhanced photocatalytic degradation of organic pollutants due to the improved intermixing taking place during the motion of TiO microengines.

Progress toward Catalytic Micro‐ and Nanomotors for Biomedical and Environmental Applications

“…Here, the motion was caused by a combined effect of diffusiophoresis and osmophoresis. Later studies observed active propulsion of the tubular TiO 2 structures . As TiO 2 exists in the form of different crystalline phases, propulsion efficiency of TiO 2 ‐based MNMs may vary, similar to that observed with the MnO 2 ‐based MNMs, discussed previously.…”

Nanoconfined Atomic Layer Deposition of TiO2/Pt Nanotubes: Toward Ultrasmall Highly Efficient Catalytic Nanorockets

“…Meanwhile, on a relatively larger scale, researchers have developed micrometer‐sized structures that can achieve autonomous chemically powered propulsion for diverse applications ranging from drug delivery to environmental remediation . Shrinking the dimensions of these small self‐propelled swimmers to the true nanometer scale is crucial for compatibility with subcellular components and synthetic molecular devices, but has seldom been investigated …”

Geometry Design, Principles and Assembly of Micromotors

“…Figure 4 d demonstrated light-control over the propulsion of microbubble-driven Ti/Cr/Pt catalytic microengines, where hydrogen peroxide fuel is degraded under local illumination of Si/Pt substrate [ 127 ]. Light powered/controlled motion can be related to several categories by using (i) semiconductor photocatalytic [ 161 , 162 , 163 , 164 , 165 , 166 , 167 ]; (ii) metallic plasmonic [ 168 , 169 ]; (iii) phototactic [ 170 , 171 ]; (iv) hybrid semiconductor-metallic swimmers [ 172 , 173 , 174 , 175 , 176 , 177 ]; (v) thermophoresis [ 178 , 179 , 180 ] and (vi) thermocapillary effects [ 181 ]. Other light controlled motors include: dual-light controlled [ 182 ] and a spectrally tunable light-driven silicon nanowires [ 183 ].…”