Effects of Cu addition on CO gas-sensing properties of TiO₂ prepared by oxidizing mechanically-synthesized TiN composites

TiN–Cu composites were synthesized in a pressurized N₂ atmosphere using a ball milling process. TiO₂ sensing materials were added with 0–8 at% Cu, which was prepared via oxidation at temperatures of 600 and 800 °C. Structural characterization was performed using X-ray diffraction, Field emission scattering electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). Cu addition promoted anatase-to-rutile transformation and grain growth, and the responses of the samples that were oxidized at 600 °C with CO gas were enhanced by adding Cu to TiO₂ compared with the unmodified TiO₂. The TiO₂ materials with 4% Cu showed the greatest response to CO of 4.1 at 1000 ppm of CO gas, which can be compared to the response value of 1.2 of unmodified TiO₂–CO gas under identical conditions. The enhancement of TiO₂ sensitivity to CO gas is believed to originate from well-dispersed metallic and Cu oxides, which are known catalysts for the oxidation of CO gas. When the oxidation temperature was increased to 800 °C, the strongly bound CuO particles dissociated, and the response changed to p-type. It is proposed that the segregation induces a conduction pathway through CuO.