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

Abstract Two different sensing materials of TiO 2 –WO 3 system with the grain size of nanometer are synthesized; one is a complete 2-nm-sized coprecipitate ((Ti,W)O 2 ) made by sol-coprecipitation of TiCl 4 and WCl 6 , and the other is a complex 8-nm-sized material (TiO 2 +WO 3 ) by mixing the sol-precipitation of TiCl 4 and WCl 6 . The TiO 2 –WO 3 system showed different characteristics between the coprecipitate and the complex material of TiO 2 and WO 3 . The sensitivity and sorption properties were improved in the coprecipitate. In the coprecipitate, the sensitivity defined as R G / R A , where R G and R A are resistance in gas ambient and in air, respectively, was about 100 for 30 ppm NO 2 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.