Layer-by-layer deposition of TiO2 nanoparticles

In this paper we report on the fabrication of nanoporous films using layer-by-layer deposition of TiO2 nanoparticles utilizing the sol-gel process. TiO2 nanoparticles with a mean diameter of 40 nm are dispersed in aqueous solutions either in the acidic or alkaline pH range. It is shown that the adsorption of the TiO2 particles is not governed by electrostatic forces as it was suspected from previous experiments of alternate adsorption with polyelectrolytes. This is concluded from the fact that no polyelectrolytes can be found in films prepared by the electrostatic layer-by-layer (ELBL) deposition method. This is proven by the use of dye-labeled polyelectrolytes for the ELBL procedure in combination with absorption spectroscopy. It is suggested that the films are formed by a sol-gel process of each layer of TiO2 nanoparticles. This is demonstrated further by the preparation of TiO2 films by alternate dipping into solutions of TiO2 nanoparticles and a buffer solution. The films obtained by this technique are characterised by AFM imaging for determination of roughness and thickness.