TiO₂/carbon nanotube composites were prepared by modified sol-gel and low temperature hydrothermal synthesis. The photocatalytic activity of as-prepared composites was evaluated by the degradation of methyl orange. The samples were characterized using X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller adsorption analysis, thermogravimetric-differential thermal analysis and UV-Vis diffuse reflectance spectroscopy. Enhanced photocatalytic activity was obtained on the composites prepared by sol-gel method and the optimum weight ratio of carbon nanotubes over titanium dioxide in the composites was founded to be 3%. It is found that calcining composites in a moderate oxidative atmosphere allowed the compatibility of sufficient crystallization and well thermal stability of the composites. Further enhancement of photoactivity was observed on TiO₂/carbon nanotube composites prepared by hydrothermal synthesis. The carbon nanotubes in the composites were virtually well covered by TiO₂. The further enhanced photoactivity can be attributed to the intimate heterojunctions between TiO₂ and carbon nanotubes, higher surface area, fine particles and the thermal stability of the composites obtained at the low hydrothermal temperature employed. The role of appropriate amount of carbon nanotubes in composites for enhanced activities was discussed.

Key words: TiO₂, carbon nanotubes, sol-gel, low temperature hydrothermal synthesis, photocatalysis