Self-catalytic synthesis of ZnO nanoparticles@SiO₂ composites with controllable fluorescence

ZnO nanoparticles@SiO₂ (ZnO NPs@SiO₂) composites have been prepared by a self-catalytic approach in a water-ethanol solution at near neutral conditions. A multifunctional precursor combining not only a silicon alkoxide and a metal carboxylate group, but also a protonated amine group was designed. The intramolecular protonated amine groups could act as catalytic sites for the hydrolysis and condensation of silicon alkoxides. Thus self-catalytic reactions would proceed spontaneously without the addition of any other catalyst. By adjusting the manner of adding the silica source, ZnO NPs with an average diameter of 2.61, 4.00, and 5.72 nm for ZnO NPs@SiO₂ composites could be controllably synthesized. Accordingly, the different ZnO NPs@SiO₂ composites displayed blue, green, and yellow three emission under ultraviolet light.