Fabrication and characterization of multilayer films based on Keggin-type polyoxometalate and chitosan

Multilayer films based on Keggin-type polyoxometalate (POM) α-SiW₁₂O₄₀]^4? (α-SiW₁₂), α-PMo₁₂O₄₀]^3? (α-PMo₁₂) and cationic chitosan have been fabricated in aqueous solution via the layer-by-layer self-assembly technique (LBL). The resulting films were characterized by UV–Vis spectra, X-ray photoelectron spectra (XPS), atomic force microscopy (AFM) and cyclic voltammetry (CV) measurements. UV–Vis spectra show that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of chitosan/POM bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. XPS spectra confirm the incorporation of chitosan and POMs into the films. AFM images indicate that the surface of the multilayer films is rather uniform and smooth. The antibacterial activities against Escherichia coli of the LBL films have also been investigated by optical density method.