Sensor de gases à base de céria modificada com Nd preparado por hidrotermal assistido por microondas para detecção de monóxido de carbono

Abstract

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.