Microwave-assisted Hydrothermal And Sol-gel Methods For The Preparation Of Nano-CeO 2 And Their Properties

CeO₂ is one kind of important light rare earth oxides,Because of its special physical and chemical properties,it is often applied in Polishing material,catalytic material and ultraviolet absorbing material,etc.When the particle size of CeO₂ reached nanometer level,comparing with ordinary CeO₂,nano-CeO₂ has incomparable material properties.In recent years,material scientist continuously researches preparation and application of nano-CeO₂,the study on CeO₂ is becoming one of the hot spots of nano-powder materials.Properties of nano-CeO₂ closely related to its purity,size,morphology,crystallinity,dispersion,specific surface area,particle size distribution,etc.In this paper,we study the preparation of nanometer CeO₂ by microwave and controllable synthesis of different morphologies CeO₂.Using microwave hydrothermal method and urea as homogeneous precipitant.In this paper we research the effects of cerium nitrate concentration,molar ratio of cerium nitrate to urea,reaction temperature,reaction time and surfactant on the morphology and particle size of CeO₂ precursor.Experimental results show that without the role of surfactants,the crystallization integrity,uniform particle size and dispersible rod-like CeO₂ precursor can be prepared.Surfactants have a great influence on CeO₂ precursor morphology and particle size,different morphology of CeO₂ precursors can be prepared under the role of different surfactants.Hollow spherical CeO₂ precursor can be prepared under the role of Citric acid.So we investigate the effect of citric acid content and optimum synthesis conditions of hollow spherical CeO₂ precursor.Effect of thermal decomposition temperature and thermal decomposition time on morphology and grain size of thermal decomposition products of hollow spherical CeO₂ precursors are investigated.The result show that spherical cerium oxide with average particle size of 500 nm can be prepared under the conditions of thermal decomposition temperature is 1050 ?and thermal decomposition time is 4 hours.In this paper,the preparation of ultrafine nano-CeO₂ by microwave assisted sol gel method,the effects of molar ratio of cerium nitrate to citric acid,gelling temperature,thermal decomposition temperature and time on ultrafine nano-CeO₂ are also studied.The effects of water bath heating and microwave-assisted heating to the morphology of xerogel and thermal decomposition products is compared.The results show that the xerogel and cerium oxide,which prepared by microwave method,has better performance.The optimum conditions are as follows: molar ratio of cerium nitrate to citric acid is 1: 4,the gelation temperature is 85 ?,the thermal decomposition temperature is 550 ?,and the thermal decomposition time is120 min.The ultrafine nano-CeO₂ wirh average particle size of 20 nm,good crystal integrity and dispersible can be prepared under optimal conditions.The specific surface area of ultrafine nano-CeO₂ is 80.229 m2/g,which can be used as catalyst matrix to further study its catalytic performance.