Study On Structure And Performance Of Rare Earth Oxide Hollow Spheres Prepared By Hydrothermal Method

Rare earth elements have excellent optical,electrical and magnetic performance,owing to their unique structure of 4f electronic and 5d air track.Compared with other materials,hollow spheres material have characteristics of high specific surface area,low density and good permeability,etc.Rare earth oxides hollow spheres is a combination of hollow inorganic spheres and rare earth oxides,so the performance of this material would be improved,and make it more widely applied.In this paper,monodispersed,uniform Ceria?CeO₂?and Yttria?Y₂O₃?hollow spheres were synthesized by hydrothermal method,and their photocatalytic degradation of methyl orange?MO?and potassium dichromate?K₂Cr₂O₇?absorption capacity were researched.The main results are as follows:1.Cerium nitrate hexahydrate?Ce?NO₃?₃·6H₂O?was selected as cerium sources,ethylene glycol aqueous solution as solvent,and polyvinylpyrrolidone?PVP?as surfactant.The best formula and technological conditions for synthesis of CeO₂ hollow spheres by hydrothermal method is determined: the amounts of Ce?NO₃?₃·6H₂O is 1 g,PVP is 0.8 g,35 ml of ethylene glycol aqueous solution,reaction temperature is 180 ?,reaction time is 22 h,and the calcination temperature is 500 ?.The CeO₂ hollow spheres with diameter of 400 nm,shell thickness around 30 nm.The precursor is multiphase material,pure CeO₂ hollow spheres with cubic fluorite structure are obtained through calcination process at 500 ? for 2 h.The BET specific surface area of CeO₂ hollow spheres was 76.86 m2g-1,pore size distribution from 3 to 5 nm.The morphology,dispersion and size of CeO₂ hollow spheres could be controlled by the amounts of Ce?NO₃?₃·6H₂O,PVP and the reaction time.The formation mechanism of CeO₂ hollow spheres is Ostwald ripening mechanism.2.CeO₂ hollow spheres synthesized by hydrothermal method have hollow structure and the high surface area,promoting the spread of the dye molecules and reduce the recombination probability of the electrons and the hole pair,so they exhibit superior performance in the degradation of methyl orange?MO?,the degradation rate of MO solution can reach 95 % after 6 h,which is superior to the commercial CeO₂ powder.When the initial concentration of Cr3+ is 50 mg/L,the optimum pH is 3,the amounts of adsorbent is 0.08 g,adsorption time is 5 h,the calcination temperature of CeO₂ hollow spheres is 500 ?.The CeO₂ hollow spheres show an excellent adsorption of K₂Cr₂O₇ solutions at room temperature and their removal rate is about 94.06 %,the maximum adsorption capacity is 5.88 mg.g-1,the adsorption process of Cr3+ on the CeO₂ hollow spheres followed pseudo-second-order kinetic models.3.Yttrium nitrate hexahydrate?Y?NO₃?₃·6H₂O?was selected as yttrium sources,urea as precipitant,ethanol aqueous solution as solvent,and PVP as surfactant.The best formula and technological conditions for synthesis of Y₂O₃ hollow nano-flowers by hydrothermal method is determined: the amounts of Y?NO₃?₃·6H₂O is 0.1 g,urea is 0.36 g,30 ml of ethanol aqueous solution,PVP is 0.8 g,reaction temperature is 180 ?,reaction time is 12 h,and the calcination temperature is 900 ?.The diameter of Y₂O₃ hollow nano-flowers is about 140 nm.The precursor is Y?OH?CO₃,pure Y₂O₃ hollow nano-flowers with cubic fluorite structure are obtained through calcination process at 900 ? for 2 h.The BET specific surface area of Y₂O₃ hollow nano-flowers was 15.46 m2g-1,pore size distribution was mainly in 21 nm.The morphology,structure of Y₂O₃ hollow nano-flowers could be controlled by the amounts of Y?NO₃?₃·6H₂O,PVP,urea and reaction time.The formation mechanism of Y₂O₃ hollow nano-flowers followed Kirkendall effect.4.The Y₂O₃ hollow nano-flowers show an excellent adsorption of K₂Cr₂O₇ solutions at room temperature,when the initial concentration of Cr³⁺ is 50 mg/L,the optimum pH is 1,the amounts of adsorbent is 0.04 g,adsorption time is 5 h,the calcination temperature of Y₂O₃ hollow nano-flowers is 900 ?.The removal rate of K₂Cr₂O₇ solutions is about 88.5 %,the maximum adsorption capacity is 11.06 mg.g-1,the adsorption process of Cr³⁺ on the Y₂O₃ hollow nano-flowers followed pseudo-second-order kinetic models.