CO and CO2 gas sensing properties of mesoporous CoAl2O4

Mesoporous CoAl2O4 was prepared by a non-aqueous solution method using aluminum chloride, cobalt nitrate and urea, dissolved in ethyl alcohol. The solvent evaporation was made by applying microwave radiation at low power. The calcination of the precursor powder at 500 °C produced CoAl2O4, which was identified by X-ray powder diffraction. The observation by transmission electron microscopy (TEM) revealed the formation of semispherical nanoparticles, having a size in the range of 40–160 nm. Mesoporosity was identified in the nanoparticles. The gas sensing characterization was performed on thick films, made with the as-prepared CoAl2O4 powder. The characterization was done in CO and CO2, using alternating current (AC) and direct current (DC). In AC, the variation of the magnitude of the impedance (|Z|) was measured at different experimental parameters. The results revealed a better response in CO, with an average variation of |Z| of 24 kΩ; whereas in CO2, was 0.37 kΩ. These values were recorded at 100 kHz and 400 °C. The dynamic and static measurements, performed in AC and DC, demonstrated that the mesoporous CoAl2O4 obtained in this work can detect variations in the concentration of CO and CO2. The results suggest the possible application of this material as CO gas sensor; however, in CO2 a limited performance was observed.