Solubility Product Driven Preparation Of Al₂O₃ Hollow Microspheres Based On Recyclable Template And Their Adsorption Performances

Al2O3 hollow microspheres and other oxides hollow structural materials have widely potential applications,based on their properties of low density,thermal insulation,high surface area,high permeability and good light scatter.In terms of synthesis of hollow structures,hard template method was considered as the most straightforward and effective route.However,there are still some problems,including damage of hollow structure during the template removal process and high cost resulted by poor recycle ability of template,limiting applications of the method.Based on this background,a new route to prepare Al2O3 hollow microspheres was presented in this thesis,in which CaMg(CO3)2 microspheres were used as template,and the gap of solubility product constant between Al(OH)3 and CaMg(CO3)2 played the role of driving force of reaction.Research on morphology and size control of CaMg(CO3)2 template,structure fabrication of Al2O3 hollow microspheres,recycle of CaMg(CO3)2 template was conducted.Moreover,influences of hollow structure of Al2O3 hollow microspheres on their adsorption properties were analysized.Besides,application of solubility product drivien mechanism in preparation of other metal oxides hollow structures was studied.The main research contents were listed below:Synthesis and morphology and size control of CaMg(CO3)2 template.CaMg(CO3)2 template was synthesized and influences of synthetic conditions on morphology and size of CaMg(CO3)2 were inveatigated.The results showed that reaction temperature,stirring time and ripening temperature had obvious influences on the morphology and size of CaMg(CO3)2 template.CaMg(CO3)2 microspheres with uniform size,regular shape and adjustable size in the range of 3-10μm can be obtained by controlling synthetic conditions.Preparation and properties study of Al2O3 hollow microspheres.Measures were taken to control the stability of CaMg(CO3)2 template in Al3+ solution,and Al2O3 hollow microspheres were prepared by using CaMg(CO3)2 as template.Influences of synthetic conditions,including surface properties of template,composition of dispersant and calcination temperature of precursor,on the properties of Al2O3 hollow microspheres were investigated.The results showed that,reaction rate between Al3+ and CaMg(CO3)2 template can be controlled and Al2O3 hollow microspheres can be prepared successfully,when ethanol was used as dispersant and solution of Al3+ was added to the reaction system dropwise.Surface properties of template affected the porosities of Al2O3 hollow microspheres.Water content of the dispersant influenced the integrity of Al2O3 hollow microspheres.Calcination temperature have effects on the crystalline phase and pore structure of Al2O3 hollow microspheresResearch on recycle of CaMg(CO3)2 template.Mg2+ and Ca2+ in the solution after preparation of Al2O3 hollow microspheres were used to recycle the CaMg(CO3)2 template,and recycle of CaMg(CO3)2 template was accomplished by adjusting the dispersant of reaction system.The results showed that reborn CaMg(CO3)2 template can not be obtained when ethanol was used as dispersant,because the ethanol in the solution affected grain growth of CaMg(CO3)2.CaMg(CO3)2 template can be recycled and Al2O3 hollow microspheres with expected structure can be obtained by using solution of Mg(NO3)2 and Ca(NO3)2 as dispersant.Adsorption properties of Al2O3 hollow microspheres.Influences of hollow structure of Al2O3 hollow microspheres on their adsorption properties were analysized via comparing with regular porous Al2O3 samples.Furthermore,their adsorption performance to anionic dyes was investigated.The results showed that the hollow structure of Al2O3 hollow microspheres can promote diffusion of dye molecules in their pores,and high surface area facilitated adsorption of dye molecules,which resulted in better adsorption performance of Al2O3 hollow microspheres than regular porous Al2O3 samples.Al2O3 hollow microspheres showed high adsorption capacity to anionic dyes,making them potential for application in the area of dye adsorption.Application of solubility product drivien mechanism in preparation of other metal oxides hollow structures.Based on thermodynamic calculation and the above experimental results,essence of the solubility product drivien mechanism of preparation of Al2O3 hollow microsphers was investigated,and its application prospect in preparation of other metal oxides hollow structures was analysized.The results showed that the gap between solubility product constant of Al(OH)3 and CaMg(CO3)2 determined the equilibrium constant of the reaction.Thermodynamic calculation results and successful preparation of CrnO3 and In2O3 hollow microspheres proved that,the solubility product drivien mechanism had potential application in preparation of other metal oxides hollow structures.