Preparation Of CeO₂ Composite Oxides And Their UV-shielding Properties

Cerium is an important rare earth element with +1.74 V redox potential. The valance of cerium ion is easily changed from Ce³⁺ to Ce⁴⁺ , or vice versa. Cerium dioxide, CeO₂ is cubic crystal with fluorite structure and shows strong absorbtion ability to ultraviolet (UV) light, good stability, low price and no harm to human body, so it can be used as good UV shielding agent. However, CeO₂ has high oxidation catalysis, poor compatibility with organic substances and can't disperse in non-polar media, so its applications are largely limited. This dissertation consists of following contents:1. The direct precipition method has been used to prepare pure nano- CeO₂ with Ce(NO₃)3·6H₂O,(NH₄)2CO₃ as precursor. Preparation conditions have experimentally been optimized with the best UV shielding properties. An (NH₄)2CO₃ solution was quickly added into the Ce(NO₃)₃ solution at the ratio of 3:2(v/v), at 40℃, reaction for 15min. Intermediate products were washed with deionized water and ethanol, then calcined at 600℃for 1h. The CeO₂ nanoparticles showed the best UV shielding properties on above mentioned preparation conditions.2. The direct precipition method has been used to prepare nano- CaO/CeO₂ with Ce(NO₃)₃·6H₂O,(NH₄)2CO₃ and Ca(NO₃)2·2H₂O as precursor. When the content of mixed calcium is 20%(molar ratio), the nano-composite powders CaO/CeO₂ has the best UV shielding properties. XRD and TEM were used to characterize the grain size of the pure CeO₂ and Ca-doped CeO₂. The particles of CaO/CeO₂ is smaller than pure CeO₂. The oxidation catalysis of nano- CeO₂ was inhibited by doping CaO based on the experimental results castor oil as catalytic degradation.3. Surface modification of nano-CaO/CeO₂ composite powders has been conducted by using silane coupling agent KH570 and corresponding changes in surface properties was analyzed. The experimental results showed that the modified composite powders could dissolve easily into organic solvents since the modified surfaces have changed from hydrophilic-oilphobic to oilphilic-hydrophobic srates. The silane coupling agent KH570 coated on the powders'surfaces has been characterized by FT-IR measurement. The mechanism for surface modification has primarily been discussed.