Extremely Fast Growth Rate of TiO2 Nanotube Arrays in Electrochemical Bath Containing H2O2

Abstract

TiO2 nanotube arrays were produced by anodization of Ti foil at 60 V in a bath with electrolytes composed of ethylene glycol (EG), ammonium fluoride (NH4F), and hydrogen peroxide (H2O2). The H2O2 was used to replace the H2O as oxygen provider to increase the oxidation rate for synthesizing highly ordered and smooth TiO2 nanotubes at a rapid rate. After a minute of oxidation, nanotubes with length of ∼2.25 μm were formed; this translated to an extremely fast rate of nanotube formation. However, length of the nanotubes did not increase linearly with time. As anodization time was increased, the rate was reduced slightly. After 3 h of anodization, 13 μm long nanotubes were formed. The nanotubes were smooth, with an average diameter of 100 nm. The extremely fast rate of nanotube growth may be attributed to the generation of radicals •OH and HO2• from H2O2, which increased the dissolution rate at the bottom of the nanotubes and accelerates the inward growth of TiO2 nanotubes. The nanotubes were then subjected to heat treatment, and their photocatalytic ability was investigated through methyl orange degradation.