Enhanced CO2-sensing response of nanostructured cobalt aluminate synthesized using a microwave-assisted colloidal method

Blue powders of nanostructured cobalt aluminate were synthesized using a microwave-assisted colloidal method applied in a non-aqueous medium, using dodecylamine as a surfactant. X-ray diffraction, UV-vis, and Raman measurements showed that single-phase CoAl2O4 was obtained when a calcination temperature of 800 °C was used. Extensive porosity was observed in the powders using scanning electron microscopy. Transmission electron microscopy studies showed that irregular-shaped nanoparticles with an average size of ∼9 nm were obtained. The gas-sensing properties were measured on thick films prepared using CoAl2O4 powder. The sensing response at different frequencies was determined by measuring the magnitude of the impedance (|Z|) in air, and CO2. The results showed that the cobalt aluminate material produced here could be used to detect concentrations of 50 and 100 ppm of carbon dioxide at temperatures of 200-250 °C with a response time of between 5 and 15 s. Better recovery times (11-25 s) and a reproducible dynamic response were also achieved.