Silica-Ceria Hybrid Nanostructures
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Silica-Ceria Hybrid Nanostructures
P. Munusamy, Shail Sanghavi, P. Nachimuthu, Donald R. Baer and S. Thevuthasan Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A. ABSTRACT A new hybrid material system that consists of ceria attached silica nanoparticles has been developed. Because of the versatile properties of silica and antioxidant properties of ceria nanoparticles, this material system is ideally suited for biomedical applications. The silica particles of size ~50nm were synthesized by the Stöber synthesis method and ceria nanoparticles of size ~2-3nm was attached to the silica surface using a hetrocoagulation method. The presence of silanol groups on the surface of silica particles mediated homogenous nucleation of ceria which were attached to silica surface by Si-O-Ce bonding. The formations of silica-ceria hybrid nanostructures were characterized by X-photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM). The HRTEM image confirms the formation of individual crystallites of ceria nanoparticles attached to the silica surface. The XPS analysis indicates that ceria nanoparticles are chemically bonded to surface of silica and possess mixture of +3 and +4 chemical states. INTRODUCTION Oxides in nanoscale exhibit unique properties that led to their use in wide range of applications in diverse fields such as biomedical imaging agent, drug delivery carrier, solid oxide fuel cells, optoelectronic applications, and as a catalyst support materials etc. [1]. Among them oxide nanoparticles coated or attached to the surface of another oxide nanostructures in a coreshell manner possess distinct physico-chemical properties [2]. Recently ceria is being studied intensely for bio-medical applications due to its mixed Ce 3+ and 4+ oxidation states [3]. However one of the major issues associated with ceria nanoparticles is the stability of them in the environment. Since they are reactive in nature either they mostly react with the environment or they agglomerate to form aggregates which are somewhat stable. As such, attaching the less stable ceria nanoparticles on a surface of another more stable larger nanoparticle support like silica helps the reduction of agglomeration and, as a result, the surface area of the less stable nanoparticles can be significantly increased. In addition to that properties of silica particles such as uniform size and shape, composition and surface functionalization can be easily controlled which allows tailoring the properties of the complete system and potentially these hybrid nanostructures can be used for diverse biomedical applications [4].
EXPERIMENTAL DETAILS Synthesis of silica-ceria hybrid nanostructures The silica-ceria hybrid nanostructure was synthesized according to a literature procedure with few modifications [5]. 0.6g of aqueous urea was added to 15 ml of as prepared silica solution (prepared by stöber synthesis method [6]) and the mixture was stirred for 15 min at 85˚C. At the end of 15minutes aqueous cerium (III) nitrate.hexahydr
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