One-step synthesis of silver nanoparticles in self-assembled multilayered films based on a Keggin structure compound

Ag nanoparticles (NPs) formed in situ by the photochemical reduction of phosphotungstic acid (H3PW12O40, PTA) under UV-irradiation in polyelectrolyte multilayer nanoreactors composed of poly(ethyleneimine)-silver ions (PEI-Ag+) and PTA fabricated on solid substrates by alternating adsorption, wherein the PTA plays the role of a UV-switchable reducing agent and an assembly reagent. Transmission electron microscopy (TEM) images show the formation of sphere-like silver NPs with sizes smaller than 12 nm in the multilayer films. Atomic force microscopy (AFM) and field emission scanning microscopy (FESEM) imply a film with a rough surface. The UV-vis characteristic absorbances of PTA and Ag NPs increase almost linearly with the number of bilayers, suggesting that the deposition process was regular and highly reproducible from layer to layer. X-Ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy ( FTIR) confirm the incorporation of PEI-Ag and PTA into the films. The multilayer films also exhibit good electrocatalytic activity for the oxidation of uric acid, which may be used in electrochemical biosensors.