Weak Polyion M.ultilayer-Assisted in Situ Synthesis as a Route toward a Plasmonic Ag/TiO2 Photocatalyst

Nanocrystalline Ag/TiO2 composite thin films were synthesized using a two-step synthesis methodology: the in situ precipitation of Ag nanoparticles followed by an in situ sol-gel reaction of titanium iso-propoxidc in a weak polyion multilayer (PEM) template formed by the layer-by-layer (LBL) self-assembly of poly(acrylic acid) (PAA) and polyallylamine (PAH). Because the PEM template is assembled from weak polyions, it contains nonionized carboxylic groups that arc able to react with the inorganics, resulting in the formation of a homogeneous Ag(x)/TiO2-PEM precursor film, where the content of Ag is controlled by repeating the Ag loading cycle. The subsequent annealing of the precursor yields nanostructured Ag(x)/TiO2 films with thicknesses controlled by the PEM template on the nanometer scale. Transmission electron, field-emission scanning electron, and atomic force microscopy methods were employed to evaluate the morphology and growth characteristics of the metallic and semiconductor nanocrystallites in the Ag(x)/TiO2 composite thin films. The as-formed Ag(x)/TiO2 composite thin films exhibited UV-visible photoactivity monitored by the decomposition of methylene blue (MB). In the near-UV range, the expected photocatalytic behavior of TiO2 is greatly enhanced because it is assisted by the near-field amplitudes of the localized surface plasmon resonance (LSPR) of the Ag nanoparticles in the Ag(x)/TiO2 films.