Preparation of silver-titanium dioxide core-shell (Ag@TiO2) nanoparticles: Effect of Ti-Ag mole ratio

Silver-titanium dioxide core-shell (Ag@TiO2) nanoparticles were prepared via a reduction reaction of silver nitrate followed by a sol-gel process of titanium tetraisopropoxide (TTIP). The silver core was prepared from 10 ml of 5-mM silver nitrate solution with hydrazine as a reducing agent, and cetyltrimethylammonium bromide as a stabilizing agent. The resulting solution was treated with 1 ml of TTIP solution in ethanol with concentration between 1, 2, 3, 4 and 5 mM (mole ratios of Ti: Ag were 2, 4, 6, 8, and 10 %, respectively). Morphology of the resulting materials was investigated by transmission electron microscope (TEM). The TEM results showed that the core-shell (Ag@TiO2) structure was found only in solutions with low Ti: Ag mole ratio (2-6 %) while the composite morphology with Ag particles randomly embedded in TiO2 matrix was found with higher Ti: Ag mole-ratio. The Ag@TiO2 particles contain silver core (diameter of 10-15 nm) surrounded by the TiO2 shell with the shell thickness of 10-20 nm in the solution with 2% mole-ratio and 20-50 nm in that with 6% mole-ratio. Optical spectrometric measurements found that the surface plasmon resonance (SPR) peak of silver nanoparticles was red-shifted from about 410 nm (in solution of silver nanoparticles) to about 425-430 nm (in the solutions of Ag/TiO2 nanoparticles) and it was not significantly affected by the content of TiO2. (C) 2012 Published by Elsevier Ltd.