Flame-made Nb- and Cu-doped TiO2 sensors for CO and ethanol

Nb- and Cu-doped TiO2 nanoparticles were produced by flame spray pyrolysis (FSP) and tested for sensing of CO and ethanol at 400 °C in dry air. The as-prepared powders were characterized by transmission electron microscopy, X-ray diffraction, Raman spectroscopy and nitrogen adsorption. Niobium stabilized the anatase phase and retarded grain growth up to 600 °C. Copper promoted rutile formation and an anatase to rutile transformation was already observed just above 400 °C during post-synthesis calcination. This was accompanied by a segregation of large (>100 nm) CuO crystals which were initially small (<5 nm) asperities on the titania surface. Pure as well as doped TiO2 showed an n-type signal to CO and ethanol. Both dopants improved the sensitivity towards CO over that of pure TiO2. In contrast, for ethanol a high increase in sensitivity was observed only for Nb/TiO2.