WO3 films modified with functionalised multi-wall carbon nanotubes: Morphological, compositional and gas response studies

Active layers for gas sensing applications have been obtained by adding oxygen plasma functionalised multi-walled carbon nanotubes (MWCNTs) to WO3 and using the drop-coating deposition method. Scanning electron micrographs showed that MWCNTs are well dispersed on the WO3 matrix. X-ray photoelectron analysis showed that by adding MWCNTs to the WO3 films the contribution of the doublet related with surface defects to the total W 4f signal increased. This gives evidence that the surface area of WO3 films increases due to the addition of MWCNTs to the film. Two different ratios of MWCNTs in WO3 (1/100 and 1/1000) were considered and the response of these sensors towards toxic gases such as nitrogen dioxide, carbon monoxide and ammonia was compared with that of WO3 and MWCNTs gas sensors. The results indicate that the detection at ambient temperature of these toxic gases using WO3-based gas sensors can be highly improved by dispersing an adequate quantity of MWCNTs into the WO3 matrix. A possible mechanism explaining the behaviour of hybrid sensors is introduced.