Composite TiO2 films modified by CeO2 and SiO2 for the photocatalytic removal of water pollutants

TiO2 particles of high photocatalytic activity immobilised on various substrates usually suffer from low mechanical stability. This can be overcome by the utilisation of an inorganic binder and/or incorporation in a robust hydrophobic matrix based on rare-earth metal oxides (REOs). Furthermore, intrinsic hydrophobicity of REOs may result in an increased affinity of TiO2-REOs composites to non-polar aqueous pollutants. Therefore, in the present work, three methods were used for the fabrication of composite TiO2/CeO2 films for photocatalytic removal of dye Acid Orange 7 and the herbicide monuron, as representing polar and non-polar pollutants, respectively. In the first method, the composition of a paste containing photoactive TiO2 particles and CeCl3 or Ce(NO3)3 as CeO2 precursors was optimised. This paste was deposited on glass by doctor blading. The second method consisted of the deposition of thin layers of CeO2 by spray coating over a particulate TiO2 photocatalyst layer (prepared by drop casting or electrophoresis). Both approaches lead to composite films of similar photoactivity that of the pure TiO2 layer, nevertheless films made by the first approach revealed better mechanical stability. The third method comprised of modifying a particulate TiO2 film by an overlayer based on colloidal SiO2 and tetraethoxysilane serving as binders, TiO2 particles and cerium oxide precursors at varying concentrations. It was found that such an overlayer significantly improved the mechanical properties of the resulting coating. The use of cerium acetylacetonate as a CeO2 precursor showed only a small increase in photocatalytic activity. On the other hand, deposition of SiO2/TiO2 dispersions containing CeO2 nanoparticles resulted in significant improvement in the rate of photocatalytic removal of the herbicide monuron.