(22d) Characterization of Titania Nanotube Photocatalysts

Recently, there has been growing interest in TiO₂ nanotubes (TNTs) as they can be used as adsorbents and catalysts in a wide range of applications. For example, they have been used as photocatalysts for decoloring toxic organic dyes. In this study, we are investigating the adsorption and photodegradation of a model dye, methylene blue, over TNTs, with empahsis on the effect of synthesis temperature on adsorption capacity and photocatalytic activity.

TiO₂ nanotubes were prepared by a hydrothermal method starting with TiO₂ (P25, Degussa) and mixing it with a concentrated NaOH aqueous solution. This mixture was then hydrothermally treated in a Teflon-lined autoclave at 90 - 170°C for 24 h. After washing with dilute HNO₃and deionized water, the nanotubes were dried at 100°C and calcined in air at 350°C.

The methylene blue adsorption capacity increased with increasing temperature and reached a maximum at 130^oC. The hotodegradation of methylene blue followed first-order kinetics, and TNTs synthesized at 120^oC showed the highest photodegradation activity. This was attributed to the alteration of superficial groups on the TNTs caused by the variation of synthesis temperature. Experiments including  adsorption equilibrium measurements, temperature-programmed desorption of ammonia,  and DRIFTs were carried out to further characterize the TNTs and develop a better understanding of  the relationship between the adsorption and photocatalytic activity of TNTs.