Gas sensing properties of Gd2O3 microspheres prepared in aqueous media containing pectin

Single phase Gd2O3 hollow microspheres were prepared by a direct aqueous solution–coprecipitation method. The synthesis was performed in presence of formic acid and pectin. The precursor dried at 170 °C was identified as gadolinium formate. The calcination at 500 °C produced single-phase Gd2O3. Hollow microspheres, with diameter between 0.7 μm and 2.5 μm were observed by SEM. Their inspection by TEM revealed that the shells of the microspheres were formed by a network of interconnected nanoparticles. Nanoporosity was also observed in these shells. The use of formic acid played a key role in the formation of Gd2O3 microspheres. The synthesis using acetic acid and pectin produced a material with an irregular shape. The CO2 and CO gas sensing characterization was performed on thick films using AC (impedance). The films were prepared by a simple deposition method, using the as-prepared microspheres. The n-type semiconductor behavior of Gd2O3 was confirmed by its response to the test gases. Repeatability and reproducibility in the detection of the gases was observed at 470 °C. A significant better performance was observed in CO2. Polarization curves qualitatively agreed with the impedance measurements.