CO sensor based on thick films of 3D hierarchical CeO2 architectures

Hollow CeO2 microspheres, having 3D architectures on their surface, were prepared by a microwave-assisted coprecipitation method. By this method, ceric ammonium nitrate was diluted in formic acid. The application of microwave irradiation produced the precipitation of a white powder, with the simultaneous emission of NO2. At low temperature, cerium formate was formed; whereas from 400 °C, CeO2 with cubic crystal structure was identified. The morphology of the samples calcined from 170 to 600 °C was of hollow microspheres, with size between 1.5 and 10 μm. Their surface displayed unique 3D architectures, which consisted of ramifications formed by the assembly of nanograins and nanoporous. Microwave irradiation played a key role in the formation of 3D hollow architectures. The effect of the concentration of ceric ammonium nitrate on the particle morphology was also investigated. Thick films were prepared by depositing a suspension of the CeO2 powder on alumina substrates. The electrical characterization in gases was performed in alternating current (AC). The films exhibited a reliable and quantitative detection of carbon monoxide from 250 °C. The effect of the applied frequency and the operating temperature was analyzed.