Synthesis Of Cobalt Oxide With Different Morphology And Their Catalytic Properties

At present, cobalt oxide have obainted extensive applications and have drawn greatattention due to their excellent potential applications in electrochemical and magnetic property,gas sensitivity, particularly in catalytic field. As far as we know, the morphology of materialshave a great influence on their properties and functions of the related devices for applications.Herein, it is very important and meaningful to improve their relative performances by meansof researching in control synthesis with preferable Co3O4morphology. In this paper, Co3O4with different and better morphology have been successfully synthesized by precipitationmethod, hydrothermal method and solvothermal method combined with calcination ofcorresponding precursors, and the possible formation mechanisms have also been discussed,respectively. Meanwhile, the catalytic properties in thermal decomposition of ammoniumperchlorate (AP) with different morphology of the products have been investigated. The maincontents are as follows:Porous sheet-like microstructure Co3O4were successfully fabricated via a facileprecipitation route without any surfactant combined with calcining sheet-like β-Co(OH)2precursors at500oC for2h. In addition, the effects of experimental conditions on themorphology of products have been studied, such as reaction temperature, solvent and alkalinesource. Furthermore, the formation mechanism for the sheet-like microstructures has beenanalyzed. Form comparative experiment, it was obvious that hydrazine hydrate andcyclohexane have a critical effect on the shape and growth of sheet-like microstructures. Asthe reaction temperature increased, the crystallization, morphology and mesoporous propertyof the products are all improved. It has been studied that porous sheet-like Co3O4microstructures exhibited high catalytic performance in the thermal decompositiontemperature of AP, particularly, Co3O4microstructures prepared at80oC in water bathdecreased the thermal decomposition temperature range of AP form284~453oC to222~295oC.Co2(CN)5NH2shuttle-like sheets were successfully synthesized by hydrothermal methodin the assistant of oleic acid, the porous shuttle-like Co3O4sheets were obtained by calciningthe prepared Co2(CN)5NH2precursors. Furthermore, it has been investigated the influence onthe morphology and composition of products, that is surfactant, solvent system, reactiontemperature, reaction time and calcination temperature. In this study, it indicated that oleic acid as structure-directing agent played a critical role in the shape of shuttle-like sheetsmicrostructure, the morphology of products changed as the ethanol concentration in thesolvent. Form the results, it was concluded that the best experimental condition for theformation of shuttle-like precursors was ethanol-water (volume ratio was1:1) mixed solventsystem by dissolving2mL oleic acid and recating at180oC for12h. It certified the pore sizesincreased and exhibited a narrow distribution with the increase of calcination temperature, aswell as the corresponding catalytic activities gradually improved. Porous shuttle-like Co3O4sheets which obtained by calcining the precursors at400oC revealed the best catalyticperformance in the thermal decomposition temperature of AP. The thermal decompositiontemperature range of AP was reduced to227~307oC by the catalysis of porous shuttle-likeCo3O4sheets.A typical solvothermal method assisted by oleylamine was used to prepareCo(CO3)0.5(OH)0.11H2O hollow microspheres with ethylene glycol working as solvent. Aftercalcining the prepared Co(CO3)0.5(OH)0.11H2O precursors at certain temperature, hollowmicrospheres Co3O4were successfully synthesized. Moreover, it has been explored the effectsof surfactant, reaction temperature, reaction time and calcination temperature on themorphology and structure of products. From the analysis, it showed that oleylamine andhexamethylenetetramine played a key role in the formation of the hollow microspheres. It wasworth pointing out that the surface of microspheres became coarser and the size ofnanoparticles which comprised of the microspheres increased, and products have a relativelylower surface-to-volume ratio at elevated calcination temperature. It was concluded that thebest hollow microspheres morphology was attained by using ethylene glycol as solvent,adding2mL oleylamine as surfactant and heating at180oC for24h. The final Co3O4wereobtained by calcining the precursors at different temperature and considerable decreased inthe thermal decomposition temperature of AP, especially, Co3O4hollow microspheres withcalcination of precursors at350oC decreased the thermal decomposition temperature range ofAP form284~453oC to220~296oC.