New Operando IR Technique to Study the Photocatalytic Activity and Selectivity of TiO2 Nanotubes in Air Purification: Influence of Temperature, UV Intensity, and VOC Concentration

The photooxidation of methanol, n-hexane, and carbon monoxide using TiO2 nanotubes (TNTs) has been investigated by a new operand IR technique. Following the photocatalytic reaction by time-resolved IR spectroscopy coupled with mass spectrometry (MS) allowed a surface study of the photocatalyst with on-line analysis of the products. Identification of the species adsorbed on the photocatalyst surface and those detected in the gas phase led to further clarification of the photooxidation mechanisms. The photocatalyst was characterized by IR, Raman, UV-visible, XRD, N-2 sorption, SEM, and TEM techniques. The activity and selectivity of the photocatalyst were determined by quantitative studies using gas-phase IR spectroscopy and MS. For comparison, photooxidation reactions using TiO2 P25 as a reference were performed under the same conditions. The effects of different parameters such as temperature, VOC concentration, and UV irradiation intensity on the reactivity and selectivity of the photocatalytic reaction were investigated. The effect of temperature was observed by TPD measurements (from room temperature to 200 degrees C). The TNT material showed a higher reactivity and CO2 selectivity than TiO2 P25.