Synthesis of AU/TiO₂ core-shell nanoparticles from titanium isopropoxide and thermal resistance effect of TiO₂ shell

On the synthesis of AU/TiO₂ core-shell structure nanoparticles, the effect of the concentration of Ti⁴⁺ on the morphology and optical property of Au/TiO₂ core-shell nanoparticles was examined. A gold colloid was prepared by mixing HAuCl₄·4H₂O and C₆H₅Na₃·2H₂O. Titanium stock solution was prepared by mixing solutions of titanium(IV) isopropoxide (TTIP) and triethanolamine (TEOA). The concentration of the Ti⁴⁺ stock solution was adjusted to 0.01-0.3 mM, and then the gold colloid was added to the Ti⁴⁺ stock solution. Au/TiO₂ core-shell structure nanoparticles could be prepared by the hydrolysis of the Ti⁴⁺ stock solution at 80°C. The size of the as-prepared Au nanoparticles was 15 nm. The thickness of the TiO₂ shell on the surface of gold particles was about 10 nm. The absorption peak of the AU/TiO₂ core-shell nanoparticles shifted towards the red end of the spectrum by about 3 nm because of the formation of the TiO₂ shell on the surface of the gold particles. The crystal structure of the TiO₂ shell showed an anatase phase. The increase in the Au crystallite size of the Au/TiO₂ nanoparticles with increasing heat treatment temperature is smaller than that in the pure Au nanoparticles. This may be due to the encapsulation of Au particles with the TiO₂ shell that prevents the growth of the nanoparticle nucleation.