TiO2 Nanotubes synthesised via Ti Electrochemical Anodization. An investigation on phase transformation of anodized TiO2 and the influences of grafted Cu (II) on morphology and photocatalytic ability.

Abstract

Titanium dioxide is a relatively cheap, non-toxic, and environmentally safe material. Its properties as a photon semi-conductor allow it to be utilised in photocatalysis. This includes applications such as wastewater treatment, where it can break down organic contaminants into CO2 and water. TiO2 nanotubes produced via Ti electrochemical anodization combine its photocatalytic abilities with the high surface area to volume ratios inherent in nano-scale materials to produce a highly efficient photocatalyst. Anodization was applied to produce amorphous TiO2 nanotube arrays. Heat treatment was performed at various temperatures to study its crystallization it into various crystalline phase compositions. XRD analysis showed that the heat treatment resulted in mixture of two phases: anatase and rutile. Anatase phase began to transform into rutile at temperatures above 700 °C. However, at this temperature, due to the phase transformation, the tubular morphology collapses, which lowers the photocatalytic efficiency. Because TiO2 has a band gap greater than 3.0 eV, it can only utilize ultraviolet light, which accounts for only 5 % of solar light. In this study, experiments were performed with the intent to develop a TiO2 nanotube photocatalyst which can act efficiently under visible light by engineering the band gap in the form of copper grafting. Nanotube arrays synthesised via anodization and annealed at 450 °C were grafted with copper ions (Cu2+) in aqueous solution containing 0.2, 2, 20, and 200 ppm CuCl2. Photocatalytic experiments were performed using these samples and showed that the most efficient photocatalyst in visible light was the 0.2 ppm grafted samples. But it was found that the efficiency decreases with increased grafting content from 0.2 ppm. A number of factors accounted for this trend, which are discussed within. This study shows that copper grafting can successfully modify TiO2 nanotubes to operate as a photocatalyst driven by visible light.