Effect of irradiation intensity and initial pollutant concentration on gas phase photocatalytic activity of TiO2 nanotube arrays

Well-organized TiO2 nanotube arrays were fabricated via one-step anodization process. The as-prepared TiO2 nanotubes were characterized by X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS) and scanning electron microscopy (SEM). Photocatalytic activity of obtained photocatalyst was studied in reaction of toluene degradation in the gas phase using low powered and low cost light-emitting diodes (UV LEDs) as an irradiation source. The effect of irradiation intensity and initial pollutant concentration on gas phase photoactivity of TiO2 nanotubes was analyzed. Obtained TiO2 nanotubes were smooth and vertically oriented with a length of about 1.7 +/- 0.05 mu m. The inner diameter and the wall thickness were 65 +/- 2 nm and 6 +/- 0.4 nm, respectively. The results showed that the initial toluene degradation rate increased (from 0.0062 up to 0.0567 mu mol/min) with raising initial toluene concentration (50-400 ppm), while too high dose of irradiation (about 50 mW/cm(2)) reduced photocatalytic toluene degradation rate. The best stability of TiO2 nanotubes in three subsequent irradiation cycles was observed for irradiation intensity of 38 mW/cm(2). Moreover, it was found that photocatalytic toluene degradation over TiO2 nanotubes showed first order kinetic behavior. (C) 2016 Elsevier B.V. All rights reserved.