Self-organized Anodic TiO2 Nanotubes: Functionalities and Applications Due to a Secondary Material

Abstract

Among various nanostructures, either electrochemically prepared or electrochemically applicable, vertically oriented, highly ordered TiO 2 nanotubular layers have attracted great scientific and technological interest in recent years. They posses a wide range of application opportunities across many fields due to the combination of their unique structure, mechanical and chemical stability, dimensions tunability, intrinsinc properties of TiO 2 , and the relatively simple and low-cost production. While many recent reviews focus on the synthesis of nanotubes, their properties and applications, there is no comprehensive report summarizing existing results on modifications of TiO 2 nanotube layers by a secondary material. Therefore, this chapter gives the state of the art and comprehensive overview on the routes for deposition of secondary materials inside and on tops of TiO 2 nanotubes by various means. Such depositions in all known cases exclusively lead either to new tube functionalities that are interesting from the fundamental point of view, or eventually to new advanced applications, most likely not plausible for tubes and deposited materials alone. Most frequently, the deposition proceeds on the very top surface of nanotube layers. However, there are techniques and tricks that allow deposition, decoration, coating or complete filling of nanotube interiors by a secondary material. The whole range of deposition techniques used until now for TiO 2 nanotube layers will be introduced and discussed. Selected results achieved for nanotube with secondary materials will be discussed in details. Finally, outlook towards future opportunities of the deposition methods for nanotube functionalizations will be given.

TiO2 Nanotube/Chalcogenide-Based Photoelectrochemical Cell: Nanotube Diameter Dependence Study

“…In the second step, we tested the set of self-organized TiO 2 nanotube layers shown in Figure as host scaffolds for potential heterostructured solar cell devices. In general, there are a few ways to achieve efficient light harvesting of TiO 2 layers in the visible spectral range by suitable chromophores: ,, bath deposition, spin-coating, electrodeposition, or atomic layer deposition. In this work we employed spin-coating for an infiltration of crystalline chalcogenide chromophore (Sn–S–Se) within the TiO 2 nanotube layers, as recently reported in literature for amorphous chalcogenide .…”

Atomic Layer Deposition for Coating of High Aspect Ratio TiO2 Nanotube Layers

“…Until now, numerous deposition approaches were reported to coat or fill the interior parts of the nanotubes, including electrodeposition, − chemical bath deposition, − spin-coating, , sputtering, − and atomic layer deposition (ALD). While ALD is one of the most promising deposition techniques for its excellent homogeneity and thickness accuracy, there have been only few reports published employing this technique for an introduction of the secondary material in the nanotube layers. − In particular, ALD has recently been reported for the deposition of Al 2 O 3 , as a secondary material, onto TiO 2 nanotubular structures for enhanced water splitting and more efficient dye sensitized solar cells . The Al 2 O 3 coating resulted in an improvement of the electrochemical and photovoltaic performance displayed, both ascribed to the passivation of the surface states that leads to a reduction of the electron–hole recombination rate at the surface of the TiO 2 nanotube layer electrode.…”

Electrochemical Engineering of Nanoporous Materials for Photocatalysis: Fundamentals, Advances, and Perspectives

“…The chemical structure of EENMs is often modified with different entities (e.g., metals, quantum dots, semiconductor oxide films, conducting polymers, chalcogenides) to tune their optical, electrical and chemical properties to achieve desired functionalities and performances for specific photocatalytic and photo-electrocatalytic applications [37,69,71].…”

“…Although ECD is limited by low deposition rate and single use of host template, this process is cost-effective, environmentally friendly and can be performed in any wet chemistry laboratory [72,101,107]. Various metals [35,108], oxides [30,109,110] and sulphides [31] can be electrodeposited to enhance the properties of EENMs for photocatalysis applications, including conductivity, chemical stability, PEC and photocatalytic properties [71].…”