The TiO2-adding effects in WO3-based NO2 sensors prepared by coprecipitation and precipitation method

Two different sensing materials of TiO2–WO3 system with the grain size of nanometer are synthesized; one is a complete 2-nm-sized coprecipitate ((Ti,W)O2) made by sol-coprecipitation of TiCl4 and WCl6, and the other is a complex 8-nm-sized material (TiO2+WO3) by mixing the sol-precipitation of TiCl4 and WCl6. The TiO2–WO3 system showed different characteristics between the coprecipitate and the complex material of TiO2 and WO3. The sensitivity and sorption properties were improved in the coprecipitate. In the coprecipitate, the sensitivity defined as RG/RA, where RG and RA are resistance in gas ambient and in air, respectively, was about 100 for 30 ppm NO2 at 340°C, which is suited for facility combustion furnace. The coprecipitated sensing materials had different resistance and grain size of 6 nm after calcination in air at 600°C for 2 h. The properties of precursor have been investigated by SEM, X-ray diffraction (XRD) and BET analyses.