Controlled Synthesis And Structure-activity Relationship Of Ceria-based Nanopowders For UV Shielding

As inorganic ultraviolet shielding material,ceria has the problem of too high catalytic performance.To develop inorganic UV shielding materials with low catalytic performance and high UV shielding performance,ceria-based nanopwoders for UV shielding controlled synthesis by a novel salt-assisted solution combustion synthesis（SSCS）is systematically studied for the first.Whereas,because of its high catalytic ability in the oxidation of organic materials,it has been rarely large-scale used in ultraviolet shielding field.The doping of Ca²⁺ions which have larger ionic size than that of Ce⁴⁺ions into ceria stabilizes the cubic fluorite structure,increases the ratio of cation/anion,and makes the ionic size ratio nearer to 0.732,which is the ideal r(Mⁿ⁺)/r(O^2-)in eight coordination oxide,and decreases the oxidation catalytic activity of ceria.However,the oxidation catalytic ability of calcia-doped ceria is still high,in order to greatly reduce the oxidation catalytic ability,calcia-doped ceria is coated with amorphous silica by means of seeded polymerization technique,the shell was produced to provide the cores with different reacting sites,to alter their conductivity and optical properties,to increase the stability of the dispersion,etc.The results show that the microstructure and property of ceria prepared by SSCS is affected by the sorts and amounts of salts,sorts and amounts of fuels,ignition temperature,calcination treatment,serosity grinding time and doping content.Compared with salt-free solution combustion synthesis,CeO₂ increase from 17.37mg²·g^-1 to 116.07 mg²·g^-1 in specific surface area,decrease from 48.46 nm to 7.25 nm in particle size,well dispersed and greatly increase in UV shielding ability.Ceria prepared by SSCS in 2x NaCl salt,ignited at 400℃and calcined at 500℃for 2 hours with best UV shielding ability.Doping with Ca²⁺resulted in a considerable decrease in catalytic activity of ceria for oxidation of castor oil,while the UV shielding properties is normally distributed with increasing doping.Doping 10mol%Ca O with ceria prepared by adjusting the solution to 3x NaCl salt,ignited at 400℃and calcined at 400℃for 1 hours resulted in the lowest catalytic performance and the best UV shielding performance of calcia-doped ceria.Coating calcia-doped ceria with amorphous silica by means of seeded polymerization technique,the oxidation catalytic ability could be greatly depressed.In brief,calcia-doped ceria nanopwoders for UV shielding prepared by SSCS and coated with amorphous silica by means of seeded polymerization technique in this work,which with high UV shielding performance,low catalytic performance,simple and scalable preparation methods,is promising to be applied in industrial ultraviolet shielding field and sunscreen field.