Gas sensors based on CeO_2 nanoparticles prepared by chemical precipitation method and their temperature-dependent selectivity towards H_2S and NO_2 gases

摘要

This work reports on the gas sensing characteristics of CeO2 nanoparticles synthesized at room temperature in the presence of various concentrations of ethanol (10-50 mL), using the chemical precipitation method. Different kinds of characterization techniques were used to probe the structural, morphological, optical and electrical properties of the various CeO2 nanoparticles. Structural and morphological features displayed nanoparticles with average crystallite sizes (i.e. 6-8 nm) and defect concentrations below 10%. The D-CeO2 (40 mL ethanol) nanoparticles showed slightly higher sensing response (the ratio between the resistance in gas and air) value of 5.5 towards H2S gas at room temperature (23 degrees C) amongst the tested interference gases (CO, IPA, CH4 and NO2). While at higher operating temperatures of 100 and 200 degrees C, response values of 2.5 and 1.1 were witnessed for the C-CeO2 (30 mL ethanol) and F-CeO2 (50 mL ethanol) based sensors towards NO2 gas, respectively. This deviation on optimal operating temperatures among the sensors with morphology or crystallite sizes variation signified that the gas selectivity and sensitivity are morphology and crystallite sizes-dependent. The correlation between the structural and optical features of CeO2 and NO2 and H2S sensing performances was discussed in detail. The findings showed that the sensor's D-CeO2 response towards H2S and sensor's F-CeO2 response to NO2 were dependent on the relative concentration of Ce3+ and oxygen vacancies, and the active surface area and defects, respectively. The findings further recognize that selective detection of ppm-level H2S and NO2 utilizing semiconductor metal oxide chemiresistive sensors remains a challenging issue.