Synthesis of nanoscale shell-core titania coated silica particles in the presence of polyether polyamine and the phase transition

The nanoscale titania coated silica was prepared via a two-step precipitating approach, where the nanoscale silica nuclei were first prepared by passing an aqueous solution of sodium silicate through an ion-exchange resin bed, then coated with the precipitation from hydrolyzed butyl titanate in an ethanol-hexane mixture at a low pH value in the presence of poly (ethylene oxide) polyamine salt (PPA) at a high temperature of 90 degreesC. In the second-step precipitating process, the spontaneously precipitated titania shell on the silica nuclei was stabilized in the suspension solution with the help of the adsorption of PPA on the particles. A possible precipitating mechanism was suggested. Furthermore, the amorphous titania shell could undergo crystallization from the amorphous to the anatase structure at a high temperature of 650 degreesC, and a further phase transition from the anatase to the rutile structure in the different sintering processes at a rising temperature of 750 degreesC.