Experimental validation of the importance of thermally stable bulk reduction states in TiO2 for gas sensor applications

Abstract

The relationship between bulk-reduction states and gas-sensing properties of TiO2 was predicted previously, but has not been validated yet experimentally. Herein, we present a chemical approach for the preparation of TiO2 nanoparticles with thermally stable bulk reduction states using porous amorphous titania as precursor. UV/vis diffuse reflectance, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) confirm that the stable bulk reduction states are the thermally stable Ti3+ ions and electron-trapped oxygen vacancies. O2-temperature programmed desorption (O2-TPD) measurements demonstrate that the presence of the bulk reduction states can obviously enhance the oxygen adsorption on titania surfaces. Furthermore, the bulk-reduced nanomaterial exhibits not only enhanced sensitivity and ultrafast response/recovery (< 3 s) for the detection of organic vapors (ethanol, methanol and acetone), but also excellent selectivity to CO against CH4 and H2. The sensing performance testing results confirm the importance of bulk reduction states in TiO2 sensors for the first time, and the enhanced gas-sensing performances for bulk-reduced TiO2 materials can be related to the enhanced oxygen absorption on TiO2 surfaces. © 2012 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.