Fabrication of Keggin type polyoxometalate ultrathin films and highly porous titanium dioxide films using layer-by-layer self assembly technique

This study reports on the fabrication of Keggin type polyoxometalate (POMs) ultrathin films and highly porous TiO2 films using Layer-by-layer self assembly technique. Multilayer films consisting of POMs (phosphomolybdic acid and silicomolybdic acid) and poly(diallyldimethyl ammonium chloride) (PDDA) are fabricated using layer-by-layer technique. The most important parameter in the fabrication of ultrathin films of Keggin type polyoxometalates self assembly is the solution ionic strength. At low ionic strength, polyoxometalate clusters tend to form a multilayer (∼3 monolayer for the two clusters studied here) between two polyelectrolyte layers. At high ionic strength, polyelectrolyte chains extend vertically, forming a 3D structure that accommodates incoming clusters. Characterization with UV-Vis spectra reveals the regular layer-by-layer growth and confirms the incorporation of PMo12 and SiMo12 into the films. The results obtained from this study can be used to guide generic assembly of polyoxometalates for different applications. Also, this study demonstrates the fabrication of highly porous and large surface area TiO2 nanoparticle films using layer-by-layer self-assembly. Multilayers of polyelectrolytes were assembled onto glass substrates to get microporous films. TiO2 nanoparticles were coated over these microporous films following methods established in the literature. Atomic force microscopy was used to monitor the morphology of the films. Using GC-FID, the photocatalytic activity of TiO2 was checked.