Systhesis And Surface Modification Of Nano-Silica Particals

In this paper, two methods for preparation of the SiO₂sphere particles wereinvestigated. The first method is the classical St ber sol-gel methods, which could makethe SiO₂of different diameter. The second method is the improved stepwise titration. Theeffect factors of those two processes were studied in the text. The experimental resultsshow that ammonia effect as a catalyst to speed up the hydrolysis of TEOS, which is themain factor of dispersion of SiO₂. The concentration of TEOS is the main factor of SiO₂particles size. The scruple water changes have not remarkable effect on the dispersion ofSiO₂particles. Moreover, deposited time gives the SiO₂particles enough time to disperseand ripen.With the prepared SiO₂, the further coated on the surface of a Gd₂O₃:Eu³⁺layerthough the Pechini sol-gel methods. The effect factors of this process were studied. Thetest results proved that obtained the core-shell particles were in spherical shape withnarrow size distribution and non-agglomeration. The concentration of PEG in thereaction solution affects the fluorescence intensity of the coated particles. Annealingtemperature is also one of the factors which can influence the fluorescence intensityof coated particles.The prepared samples of the SiO₂@Gd₂O₃:Eu³⁺particles have been characterizedby powder X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmissionelectron microscopy （TEM）, Energy Dispersive X-Ray Spectroscopy （EDS）, andphotoluminescence spectra （PL）. The results showed that the coated layers wereuniform and disperse, the average thickness of Gd₂O₃:Eu³⁺layers were10²0nm. Thecoated Gd₂O₃:Eu³⁺layer could be transformed cubic phase by annealing in air at600℃,and the Si-O-Gd bond could be formed at the particles interfaces. The nanometer SiO₂@Gd₂O₃:Eu³⁺particles have a good fluorescence performance.According to experimental data, the optimum conditions for preparing SiO₂@Gd₂O₃:Eu³⁺particles are founded. The reaction temperature is20℃, and theconcentration of PEG is0.08g/ml. The fluorescence of coated particles increases withthe increase of annealing temperature （300⁷00℃）. The coated mechanism ofSiO₂@Gd₂O₃:Eu³⁺particle is also studied. At the start of the reaction, rare earthmetal forms chelate by the citric acid. Then because of the function of the connectionof PEG, the–OH on SiO₂surface and–COOH of citric acid connected through the hydrogen bonding on the–OH of PEG. The rare earth element could be coated onSiO₂surface excellently. After high temperature heat treatment, nanometerSiO₂@Gd₂O₃:Eu³⁺core-shell materials particles are synthesized.