Ceria room temperature, dependence

Perez et al. reported the bio-active monodisperse, water-soluble, and highly crystalline dextran-coated ceria NPs with pH dependent antioxidant activity, which are made through room temperature hydrolysis in ammonia aqueous solution in the presence of dextran T-10 (Perez et al., 2008). The obtained water soluble NPs contained a ratio of Ce " "/Ce + approximately 3/2, which became 2/3 after adding some H2O2. Later, the NPs could regenerate the original ratio 10 days under pH 7.4 while there is no regeneration under pH 4. 

In spite of this, the detailed reason for the expansion on reduction of ceria is often discussed. The problem may be phrased as I) is it because the Cc -ion is bigger than the Ce -ion or 2) is it because the oxide vacancy volume is bigger than the oxide ion volume One reason for the questions is that the effective ion radius is dependent on how many nearest neighbours the ion has (its coordination number). Hong and Virkar analysed this problem, and concluded that the reason is that of point 1). They introduced the concept of an oxide vacancy radius. For ceria the oxide vacancy radius was found to be 0.1164 nm at room temperature which is significantly smaller than the radius of the oxide ion of 0.138 nm. 

The effects of temperature are difficult to discern from the analysis, as the inherent deviation associated with Auger analysis encompasses the variation observed as a function of temperature. The lack of evident temperature dependencies may be the result of the inherent reduction and oxidation properties of ceria. Ceria is capable of oxidizing at room temperature, while hydrogen reduction experiments have indicated that ceria reduces at temperatures in excess of 470 K [15]. This attribute precludes the analysis of reduction and... 

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