In this work, large 3D Ti meshes fabricated by direct ink writing were wirelessly anodized for the first time to prepare highly photocatalytically active TiO2 nanotube (TNT) layers. The use of ...bipolar electrochemistry enabled the fabrication of TNT layers within the 3D Ti meshes without the establishment of an electrical contact between Ti meshes and the potentiostat, confirming its unique ability and advantage for the synthesis of anodic structures on metallic substrates with a complex geometry. TNT layers with nanotube diameters of up to 110 nm and thicknesses of up to 3.3 μm were formed. The TNT-layer-modified 3D Ti meshes showed a superior performance for the photocatalytic degradation of methylene blue in comparison to TiO2-nanoparticle-decorated and nonanodized Ti meshes (with a thermal oxide layer), resulting in multiple increases in the dye degradation rate. The results presented here open new horizons for the employment of anodized 3D Ti meshes in various flow-through (photo)catalytic reactors.
The present work reports on the effect of thermal annealing on electrical, optical and structural properties of low aspect ratio self-organized TiO2 nanotube layers formed by anodization of Ti. The ...average inner diameter and length of the nanotubes was 100nm and 1μm, respectively. From the whole range of temperatures (300–600°C), annealing at 400°C leads to the formation of crystalline TiO2 nanotube layers with anatase structure offering best electrical and photo-electrochemical properties. Conducting atomic force microscopy studies have been explored for the first time to identify the annealing temperature of nanotube TiO2 layers with best electrical properties.
We present an optimized approach for the deposition of Al2O3 (as a model secondary material) coating into high aspect ratio (≈180) anodic TiO2 nanotube layers using the atomic layer deposition (ALD) ...process. In order to study the influence of the diffusion of the Al2O3 precursors on the resulting coating thickness, ALD processes with different exposure times (i.e., 0.5, 2, 5, and 10 s) of the trimethylaluminum (TMA) precursor were performed. Uniform coating of the nanotube interiors was achieved with longer exposure times (5 and 10 s), as verified by detailed scanning electron microscopy analysis. Quartz crystal microbalance measurements were used to monitor the deposition process and its particular features due to the tube diameter gradient. Finally, theoretical calculations were performed to calculate the minimum precursor exposure time to attain uniform coating. Theoretical values on the diffusion regime matched with the experimental results and helped to obtain valuable information for further optimization of ALD coating processes. The presented approach provides a straightforward solution toward the development of many novel devices, based on a high surface area interface between TiO2 nanotubes and a secondary material (such as Al2O3).
One-dimensional TiO2 nanotube layers with different dimensions were homogeneously decorated with 2D MoS2 nanosheets via atomic layer deposition and employed for liquid and gas phase photocatalysis. ...The 2D MoS2 nanosheets revealed a high amount of exposed active edge sites and strongly enhanced the photocatalytic performance of TiO2 nanotube layers.
•Ti films electrodeposited on Ni substrates were anodized towards TiO2 nanotubes.•TiO2 nanotubes layers on electrodeposited Ti films and Ti foils were compared.•Electrodeposited Ti films are rougher ...than Ti foils resulting in faster etching.•Faster etching rates result in slightly thinner nanotube layers and walls.•No significant differences in photocurrents of both nanotube layers were found.
Ti films electrodeposited on Ni foils from molten salts were anodized towards TiO2 nanotube formation for the first time. The resulting TiO2 nanotube (TNT) layers were compared with TNT layers prepared under identical conditions on Ti foils by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) measurements, X-ray photoelectron spectroscopy (XPS), and photocurrent measurements. No significant differences were found between the TNT layers prepared on the two different substrates. Electrodeposited Ti films prepared in this way could thus be a viable option for anodization purposes.
We present photoelectrochemical results for anodic TiO2 nanotube layers grown with different diameter sizes (21, 35, 56, and 95 nm) with a thickness of approximately 560 nm using a novel anodization ...protocol. These tube layers were utilized as highly ordered n-type conductive scaffold for the inorganic chromophore Sn–S–Se. While downscaling the nanotube diameter significantly increased the number of nanotubes per square unit (from 5.6 × 109 to 7.2 × 1010 pcs/cm2) and thus the active surface area increased as well, we found that the photoelectrochemical response in the UV light was identical and thus independent of the TiO2 nanotube diameter in the range of nanotube diameters from 35 to 95 nm. Further, we demonstrate that a heterostructured photoelectrochemical cell consisting of TiO2 nanotubes sensitized with crystalline Sn–S–Se chromophore showed higher photocurrent density (from 6 to 32 μA/cm2 for the wavelength of 460 nm) with increasing nanotube diameter size. Upon detailed SEM analyses it was revealed that Sn–S–Se was infilled in all nanotube layers approximately to one-third of the thickness. Therefore, this photocurrent increase with increasing tube diameter can be ascribed to better interfacial contact (and improved charge transport) facilitated between the chromophore and nanotube walls.
Self‐organized anodic TiO2 nanotube (TNT) layers prepared by anodization of Ti substrates have attracted great interest within the last 20 years, due to their unique properties and low‐cost ...synthesis. This mini review article aims to shortly summarize the most recent developments in the TNT layer synthesis and applications. It presents the synthesis of high aspect ratio (HAR) TNT layers in a short time by accelerating the TNT layer growth rates in lactic acid containing electrolytes. Furthermore, the etching of TNT layers towards TNT bundles of homogeneous size and single tube powders is discussed, as well as the possibility to grow TNT layers on non‐planar Ti substrates, which cannot be directly connected to the potentiostat (e.g., Ti spheres or 3D Ti meshes). As a relatively new application, the employment of TNT layers in microwave resonator sensors is introduced. Last, but not least, approaches of upscaling the TNT layer size from the laboratory scale towards significantly larger scale are outlined and reviewed.
This review reports on the most recent developments in the TiO2 nanotube layer synthesis and applications. It focuses on the synthesis of high aspect ratio layers in a short time, the etching of nanotube layers towards single nanotube powders, upscaling of the nanotube layer size, the anodization using bipolar electrochemistry and the application of the nanotube layers in microwave resistor sensors. Recent advances in TiO2 nanotube layers – a mini review of the latest developments in nanotube preparation and applications in photocatalysis and microwave sensing.
In this work, the anodization of Ti foils in closed bipolar cells is shown for the first time. Depending on the applied potential, i. e. direct or alternating potential, TiO2 nanotube (TNT) layers ...can either be prepared on one side or on both sides of a Ti foil. It is shown that due to the use of closed bipolar cells, potentials with different amplitudes can be applied within the individual two half‐cells. Additionally, different electrolytes can be used for the anodization of the two sides of a Ti substrate. Thus, the TNT layers obtained under alternating potential on both sides of a Ti foil can have completely different dimensions, i. e. TNT diameter and TNT layer thickness. Furthermore, by employing alternating potentials, black TNT layers can be synthesized on the side of the Ti foil, while being reduced during the last anodization step at negative potentials.
The anodization of Ti foils in closed bipolar cells is reported. TiO2 nanotube layers with different dimensions are synthesized on both sides of the Ti foil by using alternating potentials. Additionally, due to reduction, black TiO2 nanotubes are prepared on one side of the Ti foil.
The utilization of the anodic TiO2 nanotube layers, with uniform Al2O3 coatings of different thicknesses (prepared by atomic layer deposition, ALD), as the new electrode material for lithium-ion ...batteries (LIBs), is reported herein. Electrodes with very thin Al2O3 coatings (∼1 nm) show a superior electrochemical performance for use in LIBs compared to that of the uncoated TiO2 nanotube layers. A more than 2 times higher areal capacity is received on these coated TiO2 nanotube layers (∼75 vs 200 μAh/cm2) as well as higher rate capability and coulombic efficiency of the charging and discharging reactions. Reasons for this can be attributed to an increased mechanical stability of the TiO2 nanotube layers upon Al2O3 coating, as well as to an enhanced diffusion of the Li+ ions within the coated nanotube layers. In contrast, thicker ALD Al2O3 coatings result in a blocking of the electrode surface and therefore an areal capacity decrease.
We report on the photoelectrochemical and terahertz measurements, of the charge transport properties of 1 μm thick self‐organized TiO2 nanotube layers, prepared by the anodization of titanium. We ...provide evidence regarding the complexity of electron transport, and dynamics in the nanotubes. Shortly after photoexcitation, charge mobilites in amorphous and crystalline nanotubes are similar, but still lower compared to the bulk anatase. The mobility subsequently decreases due to trapping‐detrapping processes. The recombination rate in anatase nanotubes is much slower than in the amorphous ones, enabling the material to reach an internal photon to electron conversion efficiency exceeding 60%.
Self‐organized anodic TiO2 nanotube layers with thickness of 1 μm were investigated by photocurrent measurements and time‐resolved terahertz spectroscopy. Electron transport through the nanotube layers was explored for the amorphous and anatase state of the nanotubes. Significant differences among both structures in terms of recombination and kinetics were revealed.
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