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

• TiO2 photocatalysts were synthesized by electrochemical oxidation of titanium foil.
• The as-obtained samples possessed a high photocatalytic activity in air treatment process using UV-light-emitting diodes.
• Selected samples of ordered TiO2 nanotubes showed high activity and stability in four cycles of toluene degradation under UV-light-emitting diodes.

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 40 V, followed by 1-h calcination at 450 °C, revealed the highest photoactivity and may be used several times without any significant decrease in activity.

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