Robert P. Lynch

A Photo-Electrochemical Investigation of Self-Organized TiO2 Nanotubes

The present work investigates the photo-electrochemical behavior of different types of self-organized layers of Ti0 2 nanotubes vertically oriented along one dimension and compares it to three-dimensional nanoparticle layers of similar thicknesses. In nanotubes, the electron diffusion length is dependent on tube order and wall smoothness by way of our investigations finding that there are much greater electron diffusion lengths for nanotubes made in organic solutions compared to the nanotubes made in aqueous solutions. These superior diffusion lengths are approximately 30 times greater than those of nanoparticle layers and are accompanied by majority charge-carrier transportation times of the order of seconds. However, the conversion efficiency of the nanotubes is not adversely affected by the length of the nanotubes for layers that have a thickness of less than the electron diffusion length. This is of high significance for photo-electrochemical applications of TiO 2 that rely on electron transport processes, where the nanotube layers could provide a very high effective surface area and thickness without significant losses.

Protein-mediated synthesis of antibacterial silver nanoparticles deposited on titanium dioxide nanotube arrays

We report on an effective route to decorate titanium nanotube arrays (TiNT) with silver nanoparticles (AgNPs). In this method, surface-adsorbed antibody molecules serve as templates to bind silver ions by electrostatic interaction. The photocatalytic activity of the TiNT under UV irradiation causes the photoreduction of AgNPs to occur, and the biological template is decomposed simultaneously. This route also was successfuly applied to gold nanoparticles (starting from negatively charged metallic precursor ions). Compared to undecorated samples, the AgNPs/TiNT samples under visible light display a much higher antibacterial activity against Escherichia coli.FigureAn effective protein-mediated route to decorate Ag nanoparticles (AgNPs) in TiO2 nanotube arrays (TiNT) is reported. The photocatalytic activity of the TiNT under UV irradiation causes the photoreduction of AgNPs to occur, and the biological template is decomposed simultaneously. Compared to undecorated samples, the AgNPs/TiNT samples under visible light display a much higher antibacterial activity against Escherichia coli.

Deconvolution of the Potential and Time Dependence of Electrochemical Porous Semiconductor Formation

A layer of porous InP is grown beneath a thin dense near-surface layer when n-InP electrodes are anodised to sufficiently high potentials in 2-10 mol dm KOH [1,2]. The cyclic voltammogram (CV) shows a characteristic single anodic peak for samples with carrier concentrations of ~3-6 × 10 cm. For electrodes with a higher carrier concentration (> ~5 × 10 cm), two anodic peaks can be distinctly observed on the forward potential sweep. A novel technique is used to deconvolute the effects of potential and time on a CV and this enables us to interpret observed differences in the linear sweep voltammograms (LSVs) of InP electrodes of different carrier concentrations. Cyclic voltammograms of InP electrodes were acquired after anodization to a series of upper potentials in the potential range for porous layer formation [2]. The slopes of these voltammograms were measured in both the forward and reverse directions at the potential of scan reversal. These slope values can be used to deconvolute the effects of potential and time from the CV at any given potential. The result of this analysis, shown in Fig. 1, is a deconvolution of the contribution of potential and time on the voltammogram as a function of the applied potential during porous layer growth. Analysis of Fig. 1 shows that in the early stages of porous layer formation the increasing potential has little effect, resulting in initially low measured current. In this potential range (0.0-0.2 V in Fig. 1) we typically observe only surface pitting. Above a certain potential (the pore formation potential, Ep = 0.23 V), pore growth occurs, where resulting domains of pores continually create further current paths effectively increasing the current density. Between the first and second current peak, it is the increasing potential that directly influences the rate of current increase. This indicates that the pore growth process has already reached its maximum rate for a given potential; the process is thus self-limiting as individual porous domains have now coalesced into a single porous layer. No new current paths can now be formed, and the further passage of current leads only to a thickening of the porous layer.