Himendra Jha

A Review of Photocatalysis using Self‐organized TiO2 Nanotubes and Other Ordered Oxide Nanostructures

Photocatalytic approaches, that is the reaction of light-produced charge carriers at a semiconductor surface with their environment, currently attract an extremely wide scientific interest. This is to a large extent due to the high expectations: i) to convert sunlight directly into an energy carrier (H(2)), ii) to stimulate chemical synthetic reactions, or iii) to degrade unwanted environmental pollutants. Since the early reports in 1972, TiO(2) has been the most investigated photocatalytic material by far; this originates from its outstanding electronic properties that allow for a wide range of applications. Not only the material, but also its structure and morphology, can have a considerable influence on the photocatalytic performance of TiO(2). In recent years, particularly 1D (or pseudo 1D) structures such as nanowires and nanotubes have received great attention. The present Review focuses on TiO(2) nanotube arrays (and similar structures) that grow by self-organizing electrochemistry (highly aligned) from a Ti metal substrate. Herein, the growth, properties, and applications of these tubes are discussed, as well as ways and means to modify critical tube properties. Common strategies are addressed to improve the performance of photocatalysts such as doping or band-gap engineering, co-catalyst decoration, junction formation, or applying external bias. Finally, some unique applications of the ordered tube structures in various photocatalytic approaches are outlined.

Increased photocurrent response in Nb-doped TiO2 nanotubes

Nb-doped TiO2 nanotube (NT) layers were grown by electrochemical anodization of Ti–Nb alloys. To successfully activate Nb doping the oxide tubes need to be annealed at sufficiently high temperatures (∼650 °C). For tubes doped with 0.1 wt% Nb not only a considerable increase in the electrical conductivity but also a significantly enhanced photocurrent (superior to any pure TiO2 nanotube layer (anatase or rutile)) was obtained.

Formation of Self-Organized Superlattice Nanotube Arrays – Embedding Heterojunctions into Nanotube Walls

Formation of Self-Organized Superlattice Nanotube Arrays – Embedding Heterojunctions into Nanotube Walls

Microfabrication of an anodic oxide film by anodizing laser-textured aluminium

A simple method for the fabrication of microstructures of an aluminium anodic oxide film (anodic alumina) by anodizing laser-textured aluminium is demonstrated. In the process, the aluminium substrate was first textured by a low power laser beam, and then the textured aluminium was subjected to anodizing, to develop a continuous, thick porous layer on the textured surface. Microstructures with a depth of a few to several tens of micrometres were fabricated successfully on the anodic oxide film by using various combinations of laser power density and laser scanning speed. Removing the film from the aluminium substrate enables the fabrication of various 2D and 3D microstructures from anodic alumina.

Formation of magnetic aluminium oxyhydroxide nanorods and use for hyperthermal effects

In the present work, we show that a porous alumina template can easily be filled with magnetic nanoparticles and then be sealed by a hot water treatment (by forming an aluminium oxyhydroxide (AlOOH) sealant layer). The porous layer then can be separated from the substrate by an etch to form free magnetic AlOOH nano-capsules. The process allows for a straightforward and highly defined size control of the magnetic units and can easily be scaled up. Furthermore, as AlOOH is biocompatible and has been used as a drug adjuvant for human use, the nanorod shaped capsules are highly promising for biomedical applications such as hyperthermal effects (heating in alternating magnetic fields).

Aluminum Microstructures on Anodic Alumina for Aluminum Wiring Boards

The paper demonstrates simple methods for the fabrication of aluminum microstructures on the anodic oxide film of aluminum. The aluminum sheets were first engraved (patterned) either by laser beam or by embossing to form deep grooves on the surface. One side of the sheet was then anodized, blocking the other side by using polymer mask to form the anodic alumina. Because of the lower thickness at the bottom part of the grooves, the part was completely anodized before the complete oxidation of the other parts. Such selectively complete anodizing resulted in the patterns of metallic aluminum on anodic alumina. Using the technique, we fabricated microstructures such as line patterns and a simple wiring circuit-board-like structure on the anodic alumina. The aluminum microstructures fabricated by the techniques were embedded in anodic alumina/aluminum sheet, and this technique is promising for applications in electronic packaging and devices.