| A novel cerium-triethanolamine(TEA) complex crystal was obtained through the reaction of cerium(III) nitrate and triethanolamine. It was used as the precursor to synthesize CeO2nanoparticles, i.e., it hydrolysized homogeneously to produce CeO2nanoparticles.The molecular formula of the cerium-TEA complex was deduced to be [Ce((C2H5O)3N)(H2O)]NO3, wherein tetravalent cerium was predominante, i.e., spontaneous oxidation of cerium(III) to cerium(IV) by oxygen took place in the synthesis process of the complex. Hydrolysis of cerium(IV) cation was slown down substantially by the coordination, which facilitated the generation of a hydrated CeO2precipitate under such optimizated condition as hydrolysis temperature of25℃, concentration of0.067mol-L-1for the precursor solution and TEA/Ce(NO3)3molar ratio of8. The hydrated CeO2precipitate can be transformed finally to CeO2nanoparticles with higher crystallinity via being aged further in water at room temperature. The obtained particles showed uniform size distribution with an mean particle size of5-6nm, which was observed by transmission electron microscopy (TEM). X-ray diffraction (XRD) as well as high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) gave evidence that all of the as-synthesized nanoparticles were well crystalline in the cubic fluorite structure. X-ray photoelectron spectroscopy(XPS) demonstrated that cerium in CeO2was tetravalent.According to the results, the age process in aqueous media can substitute for the calcination at high temperature for the further dehydration and crystallization of the hydrated CeO2precipitate.CeO2nanoparticle prepared in this study showed near identical size with those prepared by the precipitation method using hexamethylenetetramine and ammonia, but its monodispersion was more excellent. The results indicated that the homogeneous precipitation method using Ce-TEA complex is an effective method to prepare monodispersed CeO2nanoparticles.In this study, property-modification effect of CeO2nanoparticles by the element yttrium(Y) and organic modification effect of the particles by the TEA realeased from the hydrolysis were also investigated.The results indicated that the homogeneous precipitation method using Ce-Y-TEA complex is effective to prepare Ce1-xYxO2-x/2(x≤0.4) nanoparticle aqueous dispersion. The as-synthesized nanoparticles were well crystalline. Yttrium was dopped into CeO2lattice and the dispersion stability, UV shielding ability and high transparency in visible light region were improved with the increase of yttrium content. When x=0.4, a sol was achieved and it showed an mean particle size of4-5nm and possessed excellent UV shielding ability and high transparency in visible light region. The obtained sol had potential applications in industrial or civil fields with high transparency being required such as acrylic varnishes, personal care products and other optical coatings.The results further indicated that under no excess TEA, the Ce-TEA complex can also hydrolysis directly to generate CeO2with particle size of5-6nm. Moreover, along with the hydrolysis at50～70℃, chemical adsorption onto the nanoparticles for the TEA released from the precursor would occurr, and the adsorption capacity was about3.0wt%, which improved greatly the lipophilicity of CeO2nanoparticles and can fulfill in situ organic surface-modification of the nanoparticles.In order to further enhance the dispersion stability and inhibit the aggregate, the monomer such as methylmethacrylate(MMA) and styrene(St) were introduced into the feed aqueous solution for hydrolysis respectively. The polymerization of the monomer was initiated after the hydrolysis in one pot, and a nano-CeO2/PMMA as well as nano-CeO2/PS organic-inorganic composite were achieved respectively.The results showed that CeO2nanoparticles were embedded into the polymethylmethacrylate (PMMA) and polystyrene(PS) matrix of the composite and dispersed homogeneously. For the obtained composite, The thermal stability and the glass transition temperature of PMMA were enhanced, which indicated the formation of the bond between the nanoparticles and the polymer chains. Moreover, under some range of the weight content, CeO2nanoparticles can improve the UV absorption ability and tensile strengh of the PMMA. Meantime, the dopping of20mol%yttrium can improve greatly the transparency in visible light region of the CeO2/PMMA composite.The prepared nano-CeO2/PMMA and nano-CeO2/PS organic-inorganic composite powders in this study had potential applications in film, coating materials and other optical materials. |
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