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

Abstract

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 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 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.