Nanocrystalline TiO2 and Halloysite clay mineral composite films prepared by sol-gel method: Synergistic effect and the case of silver modification to the photocatalytic degradation of Basic Blue- 41 azo dye in water.

Tubular halloysite clay mineral and nanocrystalline TiO₂ were incorporated in the preparation of nanocomposite films on glass substrates via sol-gel method at 450ºC. The synthesis involves a simple chemical method employing nonionic surfactant molecule as pore directing agent along with the acetic acid-based sol-gel route without addition of water molecules. Drying and thermal treatment of composite films ensure elimination of organic material and lead to the formation of TiO₂ nanoparticles homogeneously distributed on the surface of the halloysite. Nanocomposite films without cracks of active anatase crystal phase and small crystallite size on halloysite nanotubes are characterized by microscopy techniques and porosimetry methods in order to examine their structural properties. The composite halloysite-TiO₂ films with variable quantities of halloysite were examined as photocatalysts to the discoloration of Basic Blue 41 azo dye in water. These nanocomposite films proved to be very promising photocatalysts and highly effective to dye’s discoloration in spite of small amount of halloysite/TiO₂ catalyst immobilized onto glass substrates. It also has been shown that the efficiency of the halloysite/TiO₂ films could be further improved when silver particles were deposited on their surface after successful adsorption from an aqueous solution of a silver salt and UV reduction of the adsorbed ions.