**4. Conclusion**

The chapter discusses the preparation of the nanocomposites consisting of carbon nanotubes and metal oxides like titania, zinc oxide and tungsten trioxide. For the preparation of such composite, the oxygen-containing groups are grafted on the surface of the nanotubes by acid treatment. This is followed by the attachment of the metal oxides nanoparticles on the nano‐ tubes surface. The chapter also highlights the means by which the composite is character‐ ized. These include Fourier transform infrared spectroscope, X-ray powder diffraction, field emission scanning electron microscope, energy dispersive X-ray spectroscope and transmis‐ sion electron microscope.

The UV, visible light and sunlight photocatalytic activity of the CNT-based nanocomposites is higher than that of the metal oxide or mechanical mixture of the metal oxide and CNTs. CNTs are considered to be good support materials for semiconductors like TiO2, ZnO and WO3 because nanotubes provide a large surface area support with high quality active sites. Also they stabilize charge separation by trapping electrons, thereby hindering electron–hole recombination by modification of band-gap and sensitization.
