Nanocrystalline cobalt-oxide powders by solution-combustion synthesis and their application in chemical sensors

Abstract

The present study demonstrates the relationship between the combustion reaction mechanism induced by the exothermicity of the cobalt nitrate-glycine solution-combustion reactions and morphological details of the nanocrystalline Co3O4. The thermal decomposition pathway and the amount of the heat liberated in combustion are defined by the exothermic reaction between gaseous NH3 and N2O species. A direct evidence that the exothermicity of the combustion reaction plays an important role in formation of the powders with different morphology was obtained from the scanning and transmission electron microscopies. In contrast to stoichiometric reaction, where the short-string Co3O4 particles form hard agglomerates, the energetically softer 50% fuel lean reaction is responsible for weak bonds between Co3O4 particles and formation of the loose cauliflower-like agglomerates. The latter powder with the specific surface area of 64.4 m(2)/g and the average crystallite size of similar to 11 nm was used for the processing of drop-coated sensors, which showed a superior sensor response toward 20 ppm of acetone in 25% r.h. humidity and at low operating temperature of 150 degrees C.