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.

Titania (TiO2) exists in several phases possessing different physical properties. In view of this fact, we report on three types of hydrogen sensors based on individual TiO2 nanotubes (NTs) with three different structures consisting of amorphous, anatase or anatase/rutile mixed phases. Different phases of the NTs were produced by controlling the temperature of post‐anodization thermal treatment. Integration of individual TiO2 nanotubes on the chip was performed by employing metal deposition function in the focused ion beam (FIB/SEM) instrument. Gas response was studied for devices made from an as‐grown individual nanotube with an amorphous structure, as well as from thermally annealed individual nanotubes exhibiting anatase crystalline phase or anatase/rutile heterogeneous structure. Based on electrical measurements using two Pt complex contacts deposited on a single TiO2 nanotube, we show that an individual NT with an anatase/rutile crystal structure annealed at 650 °C has a higher gas response to hydrogen at room temperature than samples annealed at 450 °C and as‐grown. The obtained results demonstrate that the structural properties of the TiO2 NTs make them a viable new gas sensing nanomaterial at room temperature. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

It is proposed to use the variation of the electrolyte temperature to fabricate titania nanotubes with variable inner diameter at a constant outer diameter and an invariable package density. The anodization of Ti sheets in an ethylene glycol and HF containing electrolyte is found to allow the preparation of nanotubes with the inner diameter controlled in the range from 10 nm to more than 250 nm through the change of the electrolyte temperature from –20 °C to +50 °C. The peculiarities of the anodization process performed at low electrolyte temperatures are discussed. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)