Resumo:
Carbon monoxide gas (CO) is one of the main air pollutants emitted directly from human
activities. This gas is particularly dangerous because it is imperceptible and has no specific
symptoms: victims fall ill or even die before they realize they have been exposed to it. It
can only be detected using a sensing device. Cerium oxide has several applications due to
its high conductivity of oxygen ions and one of them is as CO sensors that use cerium
oxide films and catalysts. In this work, ceramic powders were synthesized by the
microwave-assisted hydrothermal method, obtaining pure cerium oxide nanoparticles
doped with different molar percentages of neodymium (0; 4; 8 and 12 mol %). XRD
patterns, Raman and FT-IR spectra indicate the formation of crystalline solid solutions
with a fluorite-like cubic structure, belonging to the Fm3m space group. The microscopy
images indicated that the dopant decreases the size of the particles being highly
agglomerated and with primary particulate in the nanometric scale. The UV-Vis spectra
indicated the existence of Ce3+ and Nd4+ ions, generating oxygen vacancies that reduce the
bandgap. Positron annihilation spectroscopy studies were also conducted, which showed
that as the Nd content increases, there is a structural disturbance caused by an increase in
the oxygen vacancies surrounded by Nd (defective clusters). Finally, sensing
measurements were carried out for the cerium oxide nanoparticles, where it is observed
that the analyzed samples have a fast response and recovery time at 400 °C and a good
selectivity to CO, revealing that the synthesis method was efficient in the obtaining
samples that have great potential to be applied as carbon monoxide sensors.
