The study of the growth mechanism of TiO2 nanotubes and their applications

This research project focused on the creation of nanomaterials and their applications. The main aim was to control the growth of TiO2 nanotubes with various morphologies and to investigate potential applications for controlled drug release and for photocatalytic water splitting. The electrochemical anodisation process in fluoride-containing organic electrolytes was employed to prepare vertically aligned TiO2 nanotubular arrays, with inner diameters of individual nanotubes ranging from 50 to 150 nm. A variety of morphologies was created by precise control of experimental conditions and parameters. The formation of crystal phases in the TiO2 nanotubes was controlled by the annealing temperature (in air) and monitored by powder X-ray diffraction (XRD). The fundamental anodisation parameters affecting the morphologies, such as anodisation voltage, electrolyte composition, stirring and the effect of magnetic fields were investigated. Various processing procedures that affect the anodisation process have been studied. The influence of hydroxide islands on the growth mechanism was shown by analysis of anodisation current-time profiles, contact angle measurements and SEM observations. The effect of pre-patterns on the Ti substrate was also studied. The substrate was patterned either mechanically or by Electron Beam Lithography (EBL) with polymethylmethacrylate (PMMA) as a positive photoresist. Instead of circular nanotubes, polygonal TiO2 nanotubes were formed from the mechanically patterned substrate whereas rectangular and tube-in-tube TiO2 nanotubes were formed by using EBL. The TiO2 nanotubes were used as photoanodes for photocatalytic water splitting using a photoelectrochemical cell for generating hydrogen gas. The effects of nanotube morphology and crystal structure on the efficiency of the conversion of photon energy to chemical energy were studied on samples annealed at various temperatures, and with a range of organic hole scavengers. In addition, control of the morphology was realised by surface passivation with organic thin films and by the control of the anodisation parameters. With stepwise control, bottle shaped nanotubes (nanobottles) were designed and created for their application in controlled drug release. Scanning and transmission electronic microscopy (SEM and TEM) were used to examine the structure and morphology of the nanotubes. The surface composition was studied by X-ray Photo-electron Spectroscopy (XPS) and Energy Dispersive X-ray Spectroscopy (EDX). Crystal phases were identified by XRD.