XANES studies of the formation of Ag-nanoparticles in LbL deposited polyelectrolyte thin films

Layer-by-layer polyelectrolyte multilayer thin films, composed of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were used as polymeric nanoreactors for the nucleation and growth of Ag-nanoparticles. The effects of precursor conditions like the pH on the corresponding size, distribution and fractional composition of the embedded silver were studied before, during and after reduction process by means of NaBH4. X-ray absorption near edge structure (XANES) investigations enabled to distinguish between metallic Ag in the particles, dissolved Ag+-ions and Ag+-ions coordinated with carboxylic acid groups via a metal-ion exchange mechanism. The detailed analysis of the X-ray data showed that fractional composition of the embedded silver is determined by the processing conditions of the multilayer assembly during the nucleation and growth of Ag-nanoparticle PAH/PAA multilayer films. When the unreduced Ag-loaded PAH/PAA samples were exposed to ambient light, small Ag particles were formed within the polyelectrolyte multilayer films by reduction due to UV exposure. The formation of Ag-nanoparticles was confirmed by means of TEM and the characteristic plasmon resonance absorption peak in the UV-Vis range.