Produção de CeO2 modificado com cobalto obtido pelo método hidrotermal assistido por micro-ondas

Abstract

In the last few years, the study of ceramic materials has been evolving rapidly, especially those related to so-called functional ceramics. The diverse applications involving these materials, mainly as nanoparticles, make these materials interesting in electronic components, biomedical applications and gas sensors. In the specific case of sensors based on semiconductor ceramics, efforts have been aimed at increasing stability, sensitivity and selectivity, capable of detecting low concentrations of polluting gases, flammable harmful to health and safety and that can operate in conditions optimized, in addition to reducing energy costs and response and recovery times for systems based on transition metal oxides. In this perspective, Cerium Oxide (CeO2) has been widely researched for having unique properties, such as a strong capacity to absorb and release oxygen, easy oxidation and high ion mobility. Thus, cerium oxide nanoparticles doped with cobalt (CeO2: Co) in different concentrations (0, 4, 8 and 12 mol%) were synthesized by the microwave assisted hydrothermal method. The synthesized samples were characterized using different techniques to understand their structural and sensor properties. The X-ray diffraction patterns, the Raman spectra and the Fourier transform infrared spectroscopy confirm the formation of solid crystalline solutions with cubic structure of the fluorite type, belonging to the space group Fm-3m. The synthesis method employed was effective in the production of nanoparticles, with diameters less than 2.57 nm, as presented by the Rietveld refinement, and exhibiting high crystallinity. The optical properties were investigated using visible ultraviolet spectroscopy (UV-vis). The nature of the optical absorption band was observed in the nanoparticles of pure CeO2 and doped with cobalt with band gap energy decreasing as the concentration of the dopant increased. The chemical composition of the surface of the samples was analyzed using the X-ray photoelectron spectroscopy (XPS) technique while the microstructural properties were assessed by scanning electron microscopy (FEG-SEM). Measurements of electrical resistance of the samples were used to evaluate the sensing properties of the samples, such as sensitivity, response and recovery time when exposed to carbon monoxide (CO) gas. The electrical resistance measurements when the films were exposed to gas revealed that the synthesis method was efficient in obtaining samples that have a great potential to be applied as gas sensors.