Selective NO₂ Detection of CaCu₃Ti₄O₁₂ Ceramic Prepared by the Sol-Gel Technique and DRIFT Measurements to Elucidate the Gas Sensing Mechanism

NO₂ is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. The present work reports the structural and gas sensing properties of the CaCu₃Ti₄O₁₂ compound prepared by the sol-gel technique. Rietveld refinement confirmed the formation of the pseudo-cubic CaCu₃Ti₄O₁₂ compound, with less than 4 wt% of the secondary phases. The microstructural and elemental composition analysis were carried out using scanning electron microscopy and X-ray energy dispersive spectroscopy, respectively, while the elemental oxidation states of the samples were determined by X-ray photoelectron spectroscopy. The gas sensing response of the samples was performed for different concentrations of NO₂, H₂, CO, C₂H₂ and C₂H₄ at temperatures between 100 and 300 °C. The materials exhibited selectivity for NO₂, showing a greater sensor signal at 250 °C, which was correlated with the highest concentration of nitrite and nitrate species on the CCTO surface using DRIFT spectroscopy.