Synthesis of Silica-coated Ceria Nanoparticles by Soft Solution Chemical Reactions and their UV-shielding Properties

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Ceria nanoparticles were prepared by reacting cerium chloride aqueous solution and sodium hydroxide aqueous solution at 40℃ followed by the oxidation with hydrogen peroxide and their characteristics such as morphology, oxidation catalytic activity, photocatalytic activity, UV-shielding ability and transparency in the visible light region were investigated. The morphology of the particle greatly changed depending on the solution pH and doping metal ion. Namely, the product at pH 12 and 6 consisted of rod-like particles and spherical particles, respectively. The crystallite size greatly reduced by doping with calcium ion and zinc ion. The oxidation catalytic activity also greatly decreased by doping with divalent anions. Especially, calcium ion and zinc ion were effective to reduce the oxidation catalytic activity. Both undoped ceria and doped ceria showed much lower photocatalytic activity than titania and zinc oxide. The UV-shielding ability and transparency in the visible light region of ceria nanoparticle were improved by doping with calcium ion and zinc ion. Generally, ceria is yellow, but white powder of ceria possessing excellent UV-shielding ability and transparency in the visible light region could be obtained by calcining nanoparticles of calcia-doped ceria. Titania and zinc oxide caused damages to DNA under irradiation of UV light, but the damages to DNA with undoped ceria and calcium and zinc ion doped ceria were the same level with blank test without Sample. The generation of singlest oxygen under UV irradiation determined by chemical luminescence assay was in the order zinc oxide > titania >> undoped ceria > calcium ion doped ceria = zin ion doped ceria. According to these results, it may be concluded that calcium ion doped ceria can be used as a new UV-absorbent which is excellent in the Safety to a human body.