The effect of multiwalled carbon nanotube doping on the CO gas sensitivity of TiO2 xerogel composite film

A simple sol–gel method was applied for the synthesis of 0.01 wt% multiwalled carbon nanotubes (MWCNTs)-doped TiO2 xerogel composite film. The filmʹs CO gas sensing properties were then evaluated. Doped MWCNTs were coated with TiO2 and distributed on a TiO2 xerogel matrix. The TiO2 xerogel showed an anatase structure after heat treatment at 450 °C under vacuum. The specific surface area of the composite material was larger than the pure TiO2 xerogel material. The CO gas sensitivity of the MWCNTs(0.01 wt%)-doped TiO2 xerogel composite film was found to be seven times higher than that of pure TiO2 xerogel film and to have good stability. This higher gas-sensing property of the composite film was due to both an increase of specific surface area and the n–p junction structure of the TiO2 xerogel coated on MWCNTs. The electrons generated from TiO2 after adsorption of CO gas induces electron transfer from the TiO2 to the MWCNTs. This induces a characteristic change in the MWCNTs from p-type to n-type, and the resistance of MWCNTs-doped TiO2 xerogel composite sensor is therefore decreased.