Sensing of organic vapors by flame-made TiO2 nanoparticles

Nanostructured anatase TiO2 was produced by flame spray pyrolysis (FSP) and tested for sensing of volatile organic compounds and CO at 500 degrees C. The as-prepared powders were characterized by transmission/scanning electron microscopy, X-ray diffraction and nitrogen adsorption. Titania films about 30 mu m thick on alumina substrates interdigitated with gold electrodes were prepared by drop-coating a heptanol suspension of these powders. The films showed a high signal of n-type sensor to isoprene, acetone and ethanol at concentrations ranging from 1 to 75 ppm in dry N-2/O-2 at 500 degrees C. The response (within seconds) and recovery (within minutes) times were very fast. Heat-treatment at 900 degrees C caused a nearly complete anatase to rutile transformation and a transition to p-type sensing behavior. That resulted in a poor sensor signal to all hydrocarbons tested and considerably longer recovery times than that of the anatase sensor. That rutile sensor could detect CO that the original, anatase sensor could not. For ethanol the sensor response changed back to n-type. (c) 2006 Elsevier B.V. All rights reserved.