Ordered TiO2 nanotubes: The effect of preparation parameters on the photocatalytic activity in air purification process

Vertically ordered TiO2 nanotube arrays were synthesized by anodic oxidation of titanium foil in glycerol, ethylene glycol and water-based electrolytes. The effect of electrolyte composition, anodization voltage, ultrasonic treatment and calcination time on the morphology of the resulting thin films, as well as on their photocatalytic activity in toluene removal, used as a model volatile organic compound, was investigated. Toluene, at the concentration of about 100 ppm, was irradiated over TiO2 nanotube arrays using xenon lamp and light-emitting diodes (LEDs) in four subsequent cycles. The results showed that toluene could be mostly removed from the air after 30 min of irradiation over TiO2 nanotubes (NTs), even using LEDs (375 nm) as a irradiation source. Photoactivity increased with increasing of nanotubes lengths and decreasing of crystallite size. Thus, TiO2 nanotube arrays formed in ethylene glycol-based electrolyte by applying voltage of 40V, followed by 1-h calcination at 450 degrees C, revealed the highest photoactivity and may be used several times without any significant decrease in activity. (C) 2013 Elsevier B.V. All rights reserved.