Effect of the Preparation Method on the Gas Sensing Properties of Nanostructured CoAl2O4

To study the effect of the preparation method on the gas-sensing behavior of nanostructured CoAl 2 O 4 , this oxide was prepared by three different synthesis routes. Two of them based on nonaqueous solution media employing triethanolamine and hexadecyltrimethylammonium bromide in ethanol, and the third, in an aqueous solution-polymerization method using polyvinyl alcohol and sucrose. In order to obtain solid precursor materials from the solutions, evaporation was made by applying microwave radiation. Further thermal decomposition of precursors at 600°C in air produced single-phase nanostructured CoAl 2 O 4 with the spinel cubic structure. Structural characterization was made by X-ray powder diffraction. The particle size was determined by transmission electron microscopy; the smaller nanoparticles were observed in the sample prepared with triethanolamine, with an average size of 8 nm. The gas-sensing characterization was made in thick films prepared by the screen-printing method. In CO 2 , a strong relationship between particle size and gas response was measured in the dynamic response of resistance and polarization tests. The optimal CO 2 response of the films was observed between 400 and 450°C. Even though a reliable CO 2 detection was recorded in the three films, they were insensitive to O 2 under the experimental parameters used.