Synthesis and characterization of cerium oxide nanoparticles coated with turbostratic boron nitride

A method based on a hydrothermal process was applied to obtain not only ultrafine but also well-dispersed CeO2 nanoparticles by the application of citric acid as a protective agent against particle growth. The well-defined crystallites have a narrow size distribution, and the mean size and BET specific surface area are 3.1 nm and 211 m(2) g(-1), respectively. A mixture of the condensation product of boric acid and 2,2'-iminodiethanol (diethanolamine) and cerium oxide nanoparticles has been found to yield turbostratic boron nitride (tBN) coatings on the cerium oxide surface after heating the mixture in a flow of ammonia. Formation of a tBN layer was identified using high-resolution electron microscopy and infrared and X-ray photoelectron spectroscopies. The surface tBN layer was found to be a few nanometres thick with a surface coverage of 51.2%. However, coating of cerium oxide with such a tBN layer is suitable both for whitening the colour whilst maintaining good ultraviolet absorption properties and for restraining the high oxidation activity of cerium oxide.