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

以氯化铈水溶液和氢氧化钠水溶液为原料，反应温度为40℃，过氧化氢为氧化剂，制备了纳米CeO2，并对其形貌、氧化催化活性、光催化活性、紫外光屏蔽能力和可见光透过率等性能进行了研究。纳米粒子的形貌随溶液的pH值和掺杂金属离子的不同而变化较大。也就是说，在pH值为12和6时，产物分别由棒状颗粒和球形颗粒组成。钙离子和锌离子的掺杂使微晶尺寸大大减小。二价阴离子的掺杂也大大降低了催化剂的氧化催化活性。其中，钙离子和锌离子对降低催化剂的氧化催化活性效果较好。未掺杂CeO_2和掺杂CeO_3的光催化活性均远低于二氧化钛和氧化锌。通过钙离子和锌离子的掺杂，提高了纳米CeO2的紫外光屏蔽能力和可见光区域的透明性。CeO_2一般为黄色，但通过焙烧制备的掺钙纳米CeO_2可以得到具有良好的紫外线屏蔽能力和可见光透明性的白色CeO_2粉末。在紫外光照射下，二氧化钛和氧化锌对DNA有损伤作用，而未掺杂CeO2和钙、锌离子掺杂的CeO2对DNA的损伤与空白对照无明显差异。用化学发光法测定了在紫外光照射下产生的单一氧的大小顺序为：氧化锌；氧化钛；未掺杂氧化铈；钙离子掺杂氧化铈=锌离子掺杂氧化铈。根据这些结果，可以得出结论：钙离子掺杂的CeO2可以作为一种新型的紫外线吸收剂，对人体具有良好的安全性。

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.