Investigation of Physicochemical Parameters That Influence Photocatalytic Degradation of Methyl Orange over TiO2 Nanotubes

The photocatalytic degradation of a model textile dye, methyl orange (MO), using anodized titanium dioxide (TiO2) nanotubes has been investigated. The effects of light intensity, dye concentration, external bias, pH, and nanotube dimensions (length, diameter, and wall thickness) on MO photodegradation have been examined. The application of a minimal bias of +0.0 versus saturated calomel electrode (SCE) can enhance the dye degradation at least 10 times compared to unbiased conditions for dye concentrations between 20 and 100,mu M. The overall initial dye degradation rate demonstrates three types of dependence on dye concentration over a range from 2.5-100 mu M. For lower dye concentrations (2.5-40 mu M) and natural pH (similar to 6.0) conditions, Langmuir-Hinshelwood (LH) kinetics was observed. The nanotubes diameter, calcination condition, and the anatase-to-rutile ratio in the crystalline TiO2 nanotubes together influence the photocatalytic and photoelectrochemical properties of the TiO2 nanotubes.