Self-organized TiO2 Nanotube Layers Research Articles

Photocatalytic TiO2 Nanotube Layers on 3D Substrates Using Bipolar Electrochemistry

Self-organized TiO2 nanotube (TNT) layers have attracted considerable scientific and technological interest over the past almost 20 years, due to their wide range of applications, including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of these TNT layers is usually carried out by electrochemical anodization of valve Ti metal substrates in various F--containing electrolytes using a conventional 2-electrode set-up with the Ti substrate as anode and a Pt-foil as cathode.By now, the TiO2 nanotube layer modification of Ti substrates is mainly focused on planar substrates, such as Ti foils and 2D Ti meshes, as these substrates can easily be connected to the potentiostat during anodization. However, for the real application in photocatalytic cleaners, 3D Ti substrates, such as 3D meshes or Ti spheres, are of high interest due to their significantly increased surface area compressed in a small volume.To anodize such 3D Ti substrates towards TiO2 nanotube layers, bipolar electrochemistry can be employed instead of using a conventional set-up [3-5]. In such a bipolar set-up, the Ti substrate is not directly connected to the potentiostat but placed in an electrolyte between two so-called feeder electrodes. Due to the electric field between the feeder electrodes, the Ti substrate is polarized and can be anodized if the applied potential between the feeder electrodes is high enough. This method opens the door for the preparation of TNT layers with gradients in dimensions (i.e. diameter and length of the nanotubes) [3-5] as well as for the preparation of TNT layers on Ti substrates, which cannot be directly connected to the potentiostat, e.g. small Ti spheres [6] and complicated 3D printed structures [7].In this presentation, the preparation of TNT layers on small Ti spheres [6] as well as on 3D printed Ti substrates [7] using bipolar electrochemistry will be shown. Their application in liquid and gas phase photocatalysis will be discussed. Furthermore, we will also show the possibility of using closed bipolar electrochemical cells, consisting of two closed half-cells with the Ti substrate as obstacle between the cells for the preparation of TiO2 nanotube layers with different dimensions on the two sides of a classical Ti foil [8].

Large-Scale Anodic TiO2 Nanotube Layers: Gas Phase Photocatalysis and Virus Killing

Self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheets in various electrolytes.By now, the synthesis of TiO2 nanotube layers with different nanotube dimensions (diameter, length) and the application of these nanotube layers is well established on the laboratory scale. However, for real applications outside the laboratory scale, such as photocatalysis [3], TiO2 nanotube layers of much larger size are necessary. To date, just a few efforts were carried out to scale up the size of the nanotube layers to more than a few cm2 [3-7] due to the difficulty of controlling the parameters of the anodization process on a larger scale. The main challenge is the huge current received during the anodization of large substrates. This, in turn, leads to an increase in the electrolyte temperature that may result in dielectric breakdown of the growing nanotube layers.In this presentation, the preparation of TiO2 nanotube layers on larger area titanium substrates (dozens of cm2) will be discussed, taking into account the control of the anodization parameters. The TiO2 nanotube layers with different thicknesses and nanotube diameters were employed for gas phase photocatalysis, following the ISO standards [3,8]. In addition, results from antivirotic tests of these layers will be demonstrated. Experimental details and photocatalytic results will be presented and discussed.

Bipolar Anodization for the Synthesis of TiO2 Nanotube Layers: New Concepts and Cell Designs

Self-organized TiO2 nanotube (TNT) layers have attracted considerable scientific and technological interest over the past almost 20 years, due to their wide range of applications, including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of these TNT layers is usually carried out by electrochemical anodization of valve Ti metal substrates in various F--containing electrolytes using a conventional 2-electrode set-up with the Ti substrate as anode and a Pt-foil as cathode.By now, the TiO2 nanotube layer modification of Ti substrates is mainly focused on planar substrates, such as Ti foils and 2D Ti meshes, as these substrates can easily be connected to the potentiostat during anodization. However, for the real application in photocatalytic cleaners, 3D Ti substrates, such as 3D meshes or Ti spheres, are of high interest due to their significantly increased surface area compressed in a small volume.To anodize such 3D Ti substrates towards TiO2 nanotube layers, bipolar electrochemistry can be employed instead of using a conventional set-up [3-5]. In such a bipolar set-up, the Ti substrate is not directly connected to the potentiostat but placed in an electrolyte between two so-called feeder electrodes. Due to the electric field between the feeder electrodes, the Ti substrate is polarized and can be anodized if the applied potential between the feeder electrodes is high enough. This method opens the door for the preparation of TNT layers with gradients in dimensions (i.e. diameter and length of the nanotubes) [3-5] as well as for the preparation of TNT layers on Ti substrates, which cannot be directly connected to the potentiostat, e.g. small Ti spheres [6] and complicated 3D printed structures [7].In this presentation, the preparation of TNT layers on small Ti spheres [6] as well as on 3D printed Ti substrates [7] using bipolar electrochemistry will be shown. Their application in liquid and gas phase photocatalysis will be discussed. Furthermore, we will also show the possibility of using closed bipolar electrochemical cells, consisting of two closed half-cells with the Ti substrate as obstacle between the cells for the preparation of TiO2 nanotube layers with different dimensions on the two sides of a classical Ti foil [8].

Magnetically guidable single TiO2 nanotube photocatalyst: Structure and photocatalytic properties

The influence of annealing temperature, the crystallinity, textural properties of magnetically guidable anodic TiO2 nanotubes in form of single tube powders on the photocatalytic decomposition of model organic dye is investigated for the first time. The powders were prepared from self-organized anodic TiO2 nanotube layers (grown on Ti) by etching in piranha solution, detaching them from the Ti substrate, and annealing in a wide range of temperatures (400–900 °C). The nanotubular shape was preserved up to 800 °C. Powders annealed up to 800 °C did not contain any detectable rutile phase, which is unique among other TiO2 nanomaterials at this temperature. Part of the obtained TiO2 ST-NT powders was decorated with Fe3O4 nanoparticles using an oleic acid-based synthesis. The TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were characterized in terms of morphology, crystallinity, and specific surface area. Finally, all materials were exploited for the photocatalytic decomposition of a model dye. The best photocatalytic performance of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders were obtained at annealing temperatures of 600 and 700 °C, respectively. The synergy resulting from annealing, crystallite size, and specific surface area enhances the photocatalytic activity of TiO2 ST-NT and TiO2 ST-NT@Fe3O4NPs powders under UV light. This approach goes beyond the classical Kasuga alkaline hydrothermal approach, enabling the preparation of large quantity of TiO2 nanotubes without any impurities (such as e.g. Na or Ca content resulting from the Kasuga approach).

Large-Scale Synthesis of Photocatalytic TiO2 Nanotube Layers

Self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheets in various electrolytes.By now, the synthesis of TiO2 nanotube layers with different nanotube dimensions (diameter, length) and the application of these nanotube layers is well established on the laboratory scale. However, for real applications outside the laboratory scale, such as photocatalysis [3], TiO2 nanotube layers of much larger size are necessary. To date, just a few efforts were carried out to scale up the size of the nanotube layers to more than a few cm2 [3-7] due to the difficulty of controlling the parameters of the anodization process on a larger scale. The main challenge is the huge current received during the anodization of large substrates. This, in turn, leads to an increase in the electrolyte temperature that may result in dielectric breakdown of the growing nanotube layers.In this presentation, the preparation of TiO2 nanotube layers on larger area titanium substrates (dozens of cm2) will be discussed, taking into account the control of the anodization parameters. The TiO2 nanotube layers with different thicknesses and nanotube diameters were employed for gas phase photocatalysis, following the ISO standards [3,8]. Experimental details and photocatalytic results will be presented and discussed.

Bipolar Electrochemistry for the Synthesis of Anodic TiO2 Nanotube Layers

Self-organized TiO2 nanotube (TNT) layers have attracted considerable scientific and technological interest over the past 17 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of these TNT layers is carried out by electrochemical anodization of valve Ti metal substrates in various F--containing electrolytes using a conventional 2-electrode set-up with the Ti substrate as anode and a Pt-foil as cathode.Instead of using a conventional set-up, also bipolar electrochemistry can be employed for the anodization of valve metals [3-7]. In this set-up, the Ti substrate is placed in an electrolyte between two so-called feeder electrodes, which are connected to the potentiostat. Due to the electric field between the feeder electrodes, the Ti substrate is polarized. If the applied potential between the feeder electrodes is high enough, redox reactions can be driven on the Ti substrate. This method opens new doors for the preparation of TNT layers with gradients in dimensions (i.e. diameter and length of the nanotubes) [3-5] as well as for the preparation of TNT layers on Ti substrates, which cannot be directly connected to the potentiostat, e.g. Ti spheres [8].In this presentation, the preparation of TNT layers on small Ti spheres [8] as well as on 3D printed Ti substrates [9] using bipolar electrochemistry will be shown and discussed. Furthermore, we will also show the possibility of using closed bipolar electrochemical cells, consisting of two closed half-cells with the Ti substrate as obstacle between the cells [10].

Large-Scale Synthesis of Photocatalytic TiO2 Nanotube Layers

Self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheets in various electrolytes.By now, the synthesis of TiO2 nanotube layers with different nanotube dimensions (diameter, length) and the application of these nanotube layers is well established on the laboratory scale. However, for real applications outside the laboratory scale, such as photocatalysis [3], TiO2 nanotube layers of much larger size are necessary. To date, just a few efforts were carried out to scale up the size of the nanotube layers to more than a few cm2 [3-7] due to the difficulty of controlling the parameters of the anodization process on a larger scale. The main challenge is the huge current received during the anodization of large substrates. This, in turn, leads to an increase in the electrolyte temperature that may result in dielectric breakdown of the growing nanotube layers.In this presentation, the preparation of TiO2 nanotube layers on larger area titanium substrates (dozens of cm2) will be discussed, taking into account the control of the anodization parameters. The TiO2 nanotube layers with different thicknesses and nanotube diameters were employed for gas phase photocatalysis, following the ISO standards [3,8]. Experimental details and photocatalytic results will be presented and discussed.

Bipolar Electrochemistry for the Synthesis of Anodic TiO2 Nanotube Layers

Self-organized TiO2 nanotube (TNT) layers have attracted considerable scientific and technological interest over the past 17 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of these TNT layers is carried out by electrochemical anodization of valve Ti metal substrates in various F--containing electrolytes using a conventional 2-electrode set-up with the Ti substrate as anode and a Pt-foil as cathode.Instead of using a conventional set-up, also bipolar electrochemistry can be employed for the anodization of valve metals [3-7]. In this set-up, the Ti substrate is placed in an electrolyte between two so-called feeder electrodes, which are connected to the potentiostat. Due to the electric field between the feeder electrodes, the Ti substrate is polarized. If the applied potential between the feeder electrodes is high enough, redox reactions can be driven on the Ti substrate. This method opens new doors for the preparation of TNT layers with gradients in dimensions (i.e. diameter and length of the nanotubes) [3-5] as well as for the preparation of TNT layers on Ti substrates, which cannot be directly connected to the potentiostat, e.g. Ti spheres [8].In this presentation, the preparation of TNT layers on small Ti spheres [8] as well as on 3D printed Ti substrates [9] using bipolar electrochemistry will be shown and discussed. Furthermore, we will also show the possibility of using closed bipolar electrochemical cells, consisting of two closed half-cells with the Ti substrate as obstacle between the cells [10].

Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

New Protocols for the Synthesis of Anodic TiO2 Nanotube Layers

Self-organized TiO2 nanotube (TNT) layers have attracted considerable scientific and technological interest over the past 17 years motivated for their wide range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of these TNT layers is carried out by electrochemical anodization of valve Ti metal substrates in various F--containing electrolytes using a conventional 2-electrode set-up with the Ti substrate as anode and a Pt-foil as cathode.Instead of using a conventional set-up, also bipolar electrochemistry can be employed for the anodization of valve metals [3-7]. In this set-up, the Ti substrate is placed in an electrolyte between two so-called feeder electrodes, which are connected to the potentiostat. Due to the electric field between the feeder electrodes, the Ti substrate is polarized. If the applied potential between the feeder electrodes is high enough, redox reactions can be driven on the Ti substrate. By using electrolytes conventionally employed for the anodic TNT layer synthesis, TNT layers can also be produced using bipolar electrochemistry. This method opens new doors for the preparation of TNT layers with gradients in dimensions (i.e. diameter and length of the nanotubes) [3-5] as well as for the preparation of TNT layers on Ti substrates, which cannot be directly connected to the potentiostat, e.g. Ti spheres [8].In this presentation, the preparation of TNT layers on small Ti spheres using bipolar electrochemistry will be shown and discussed [8]. Furthermore, we will also show the possibility of using closed bipolar electrochemical cells, consisting of two closed half-cells with the Ti substrate as obstacle between the cells.

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 15 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will demonstrate the photocatalytic performance of recently developed single-wall TiO2 nanotubes and single-tube TiO2 powders [8]. We will also show that various modifications of nanotube ssecondary materials have a positive influence on photo-electrochemical properties of nanotube layers [9,10]. Experimental details and some recent photocatalytic results will be presented and discussed.

Secondary Material Modified Anodic TiO2 Nanotube Layers As Efficient Gas Sensors

Gas sensors are extensively used in medical, automotive, agriculture, biogas, and mining industry for safety and environmental monitoring, including the detection of toxic compounds to prevent hazardous emission and explosion as well as air quality monitoring. 1D nanomaterials have shown great potential for sensor preparation due to their high surface-to-volume ratios resulting in countless absorption sites, and fast diffusion of gas molecules. The 1D geometry also facilitates the charge transport process [1,2].Among 1D nanomaterials, self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest due to their wide possible range of applications including (photo-) catalysis, solar cells, hydrogen generation, biomedical uses or sensors [3,4]. The synthesis of the 1D TiO2 nanotube layers is usually carried out by electrochemical anodization of valve Ti metal sheets in various electrolytes. Compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal), anodic TiO2 nanotube layers have the advantage of being self-ordered with the nanotube openings on the top of the nanotube layer and being well-adhered to the Ti metal substrate, which can further be used as back contact for applications. Furthermore, anodic TiO2 nanotube layers can be produced with tunable tube dimensions [4]. Atomic Layer Deposition (ALD) can be used to produce conformal and homogenous coatings of thin layers of secondary materials an TiO2 nanotube layers, with precise control of the coating thickness, according to the deposition cycles [5]. Therefore, very thin films matching the thickness of the Debye length of a material can be deposited by ALD on the high surface area TiO2 nanotube layers giving the possibility for high sensitivity semiconductor gas sensors.The presentation will focus on the coating of anodic TiO2 nanotube layers with secondary materials using ALD and the possible use for low concentration gas sensing. Such secondary materials are, for instance, SnO2 [6] and ZnO [7]. The produced heterostructures show excellent sensing behavior for NO2 [6], in case of SnO2 coated TiO2 nanotube layers, and for ethanol [7], in case of ZnO coated TiO2 nanotube layers.

Intrinsically Ru-Doped Suboxide TiO2 Nanotubes for Enhanced Photoelectrocatalytic H2 Generation

In the present research, we investigate the synergistic effects of Ru-doping and Ar/H2 reduction treatment on the photoelectrochemical water splitting performance and hydrogen evolution rate of TiO2 nanotube array photoelectrodes. The Ti–Ru alloy with 0.2 at. % Ru was used to grow anodic self-organized Ru-doped TiO2 nanotube layers. An ideal synergy between Ar/H2 reduction treatment and Ru-doping results in the extended absorption toward the visible light region and improved photoelectrocatalytic activity. The black Ru-doped TiO2–x photoanode’s water splitting rate improves remarkably (∼ninefold) compared to the black TiO2–x sample (∼twofold). Moreover, the black Ru-doped TiO2–x photoanode shows a considerable increase in the H2 production rate (1.91 μmol h–1 cm–2) compared with the pristine TiO2 nanotube layer (0.044 μmol h–1 cm–2). We have also developed an ab initio model of pristine, Ru-doped, and Ru-doped hydrogenated TiO2 nanotubes to rationalize our experimental findings from the theoretical perspective.

Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 13 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

Recent Progress in Anodic TiO2 Nanotube Layer Synthesis

Over the past 15 years, self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest due to their wide possible range of applications including (photo-) catalysis, hydrogen generation and biomedical uses [1,2]. The synthesis of the 1D TiO2 nanotube layers is usually carried out by electrochemical anodization of valve Ti metal sheets in various electrolytes.The advantage of anodic TiO2 nanotube layers compared to TiO2 nanotubes prepared by other methods (e.g. hydrothermal) are the tunability of dimensions, their directionality, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials [2]. However, by now most publications report on the nanotube layer production on the laboratory scale, i.e. on Ti substrates of a few cm2.The presentation will focus on the recent progress in the TiO2 nanotube layer synthesis. We will show and discuss a possible upscaling of the nanotube layers towards areas of dozens of cm2 [3], taking into account the control of the anodization parameters. Furthermore, we will discuss the use of bipolar electrochemistry for the preparation of TiO2 nanotube layers on small Ti objects which cannot be connected to the potentiostat [4], as well as the selective etching of anodic TiO2 nanotube layers towards single-wall nanotube layers [5] and single nanotubes [6], where nanotubes are separated from one another into tube powders.

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 13 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet.Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials.One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4].The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

Self-organized TiO2 nanotube layer on Ti–Nb–Zr alloys: growth, characterization, and effect on corrosion behavior

Ti alloys are widely applied in implanted biomedical devices due to their unique mechanical and biological performances. A strategy employed to improve bone integration on orthopedic and dental implants is to grow a self-organized TiO2 nanotube layer on the surface of titanium alloy implants. This paper describes the formation of self-organized TiO2 nanotubes on Ti–35Nb–2Zr and Ti–35Nb–4Zr alloys by the anodization process, as well as the effects of Zr content on TiO2 phase stability. The morphological and chemical characteristics of the nanotubes were analyzed by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron microscopy. In addition, a comparison was made of the electrochemical stabilities of TiO2 nanotube-coated surfaces and surfaces without nanotubes, which revealed higher corrosion resistance for the nanotube-modified surface. The electrochemical impedance spectroscopy results were fitted with two-time constant equivalent circuit representing the barrier layer (nanotube bottom) and the porous layer (nanotube wall). The addition of Zr suppressed ω-phase formation, preserving the alloy’s low elastic modulus (64 GPa). This Zr addition also delayed the anatase-to-rutile transformation and slightly increased the nanotubes’ length to 1.14 µm. These features make the Ti–35Nb–4Zr alloy a very good candidate for use in the biomedical field, especially for applications that require low elastic modulus with enhanced corrosion resistance.

Noble Metal Decorated Anodic TiO2 Nanotubes: Excellent (Electro)Catalyst

The synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. The most established member of this group of materials is nanoporous Al2O3, which has been prepared two decades ago by anodic oxidation of Al into perfectly ordered, honeycomb-like porous structures employing suitable electrochemical conditions [1]. Owing to the flexibility of the pore diameter/length and the relative ease of the Al2O3 dissolution, its porous membranes have been since than widely used as template material of choice for a range of materials [2-4]. Self-organized TiO2 nanotube layers have received the highest attention after Al2O3 motivated by its range of applications, including photocatalysis, water splitting, solar cells and biomedical uses. Very significant research efforts have led to reproducible synthesis of self-organized TiO2 nanotube layers by means of anodic oxidation, during which the starting Ti substrate is converted into a highly-ordered nanotubular layer by anodization in suitable electrolytes [5-8]. Many new applications can be derived upon modification of the nanotubes by decoration, filling or coating by secondary materials [9]. Atomic layer deposition (ALD) has been shown to be an effective technique to coat TiO2 nanotube layers homogenously with secondary materials or to decorate them with noble metals [9]. The resulting structures offer many advantages and opportunities in various applications. TiO2 nanotubes in particular appeal as highly ordered electron-conductive supports for noble metal particles. This presentation will focus in detail on the decoration of the nanotube layers of different aspect ratios by noble metals using ALD. We will show and discuss our recent catalytic results on water splitting [10] and electrocatalytic results on the oxidation of methanol [11].

(Invited) Anodic TiO2 Nanotube Layers: Efficient Photocatalyst

The self-organized TiO2 nanotube layers have attracted considerable scientific and technological interest over the past 13 years motivated by their possible range of applications including photocatalysis, solar cells, hydrogen generation and biomedical uses [1,2]. The synthesis of these 1D TiO2 nanotube layers is carried out by a conventional electrochemical anodization of valve Ti metal sheet. Among other TiO2 nanomaterials, these nanotube layers stand out due to their directionality, tunability of dimensions, ability to absorb significant amount of incident light and the possibility to utilize nanotube interiors and exteriors for decoration-coating of secondary materials. One of the most significant applications of TiO2 nanomaterials is photocatalysis, which is very effective to decompose various pollutants (e.g. dyes) and kill bacteria [3,4]. The presentation will focus on the utilization of the nanotube layer for photocatalytic removal of various species in the liquid phase [5, 6] as well as gas phase [7]. We will also show that various secondary materials have a positive influence on photo-electrochemical properties of nanotube layers [8, 9]. Experimental details and some recent photocatalytic results will be presented and discussed.

(Invited) A New Perspective for Photoelectrochemical Water Splitting: Black TiO2 Nanotubes

In the past decade, anodically formed self-organized TiO2 nanotube layers attracted considerable scientific interest (see e.g. reviews [1,2]). This is mainly due to the fact that these layers combine the defined nanotubular geometry with a broad range of functional features inherent to TiO2. Particularly in photoelectrochemical water splitting nanotubular layers have shown remarkable results. The presentation will first give an overview of the most promising features of classic nanotube layers for photocatalysis and then focus on TiO2 nanotube (NT) arrays, converted by a high pressure H2 treatment to anatase-like "black titania"[3,4]. This modification shows a remarkable high open-circuit photocatalytic hydrogen production rate without the presence of any cocatalyst. Other attempts to form black titania, namely using classic reduction treatments (e.g., atmospheric pressure H2/Ar annealing) do not show this surprising effect. We will discuss the main difference caused by the high H2 pressure annealing and the origin of this outstanding activity of black titania. REFERENCES Roy, S. Berger, P. Schmuki, Angew. Chem. Int. Ed. (2011), 2904Lee, A. Mazare, P. Schmuki, CHEMICAL REVIEWS, 114 (2014) 9385Liu, P. Schmuki et.al. Nano Letters, 14 (2014) 3309Liu, P. Schmuki et.al. 53 (2014) 14201