Enhancement of photocatalytic activity of mesoporous TiO 2 by using carbon nanotubes

Abstract

Titanium dioxide/carbon nanotubes (TiO 2/CNTs) composites were prepared with the aid of ultrasonic irradiation. Products of different TiO 2:CNTs molar ratio were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) adsorption analysis, thermogravimetric and differential thermal analysis (TGA–DSC), photoluminescence (PL) and UV–vis spectroscopy measurements (UV–vis). The photocatalytic activity was evaluated by the degradation of acetone and by the detection of the hydroxyl radical (·OH) signals using electron paramagnetic resonance (EPR). It is found that the crystalline TiO 2 is composed of both anatase and brookite phases. The agglomerated morphology and the particle size of TiO 2 in the composites change in the presence of CNTs. The CNTs in the composites are virtually all covered by TiO 2. Other than an increase of the surface area, the addition of CNTs does not affect the mesoporous nature of the TiO 2. Meanwhile, more hydroxyl groups are available on the surface of the composite than in the case of the pure TiO 2. The higher the content of CNTs, there is more effective in the suppression of the recombination of photo-generated e −/h + pairs. However, excessive CNTs also shield the TiO 2 from absorbing UV light. The optimal amount of TiO 2 and CNTs is in the range of 1:0.1 and 1:0.2 (feedstock molar ratio). These samples have much more highly photocatalytic activity than P25 and TiO 2/activated carbon (AC) composite. The mechanism for the enhanced photocatalytic activity of TiO 2 by CNTs is proposed.