Large scale photochemical synthesis of M@TiO2 nanocomposites (M = Ag, Pd, Au, Pt) and their optical properties, CO oxidation performance, and antibacterial effect

Well-dispersed M@TiO2 (M = Ag, Pd, Au, Pt) nanocomposite particles with a diameter of 200–400 nm can be synthesized on a large scale by a clean photochemical route which does not require any additives using spherical rutile nanoparticles as a support. The sizes of Pt, Au, and Pd nanoparticles formed on the surface of TiO2 particles are about 1 nm, 5 nm, and 5 nm, respectively, and the diameter of Ag nanoparticles is in the range 2–20 nm. Moreover, the noble metal nanoparticles have good dispersity on the particles of the TiO2 support, resulting in excellent catalytic activities. Complete conversion in catalytic CO oxidation is reached at temperatures as low as 333 and 363 K, respectively, for Pt@TiO2 and Pd@TiO2 catalysts. In addition, the antibacterial effects of the as-synthesized TiO2 nanoparticles, silver nanoparticles, and Au@TiO2 and Ag@TiO2 nanocomposites have been tested against Gram-negative Escherichia coli (E. coli) bacteria. The results demonstrate that the presence of the TiO2 matrix enhances the antibacterial effect of silver nanoparticles, and the growth of E. coli can be completely inhibited even if the concentration of Ag in Ag@TiO2 nanocomposite is very low (10 μg/mL).