Photocatalytic and bactericide properties of Ag-doped TiO2 coatings.

ROLDÁN, V.; DE OÑA, P.; FACCENDINI, P. L.; CASTRO, Y.; DURÁN, A.; LAGIER, C. M.; GRAU, R.; PELLEGRI, N.

Madrid

Conferencia; XVll International Sol-Gel Conference; 2013

International Sol-Gel Society

Titanium dioxide (TiO2) is an interesting material to use in ambient purification because of their photocatalytic and bactericide properties. Their efficiency is limited by the redox potential and the lifetime of the electron-hole pairs. Thus, are of increase interest the strategies to change these characteristics to improve the efficience. These strategies include the generation of vacancies, manipulation of crystalline structure and doping with metals between others. In this work we measure the photocatalytic and bactericide properties of TiO2 coatings doped with silver nanoparticles. Also, we study the mechanisms involved in the enhancement of these properties by silver nanoparticles. TiO2 coatings were obtained by the sol-gel technique. To obtain Ag-doped TiO2 coatings, silver nanoparticles were previously prepared by a colloidal synthesis and then added to the TiO2 precursor sol. Also, mesoporous coatings were obtained by the EISA method. All TiO2 coatings were deposited by dipping onto a glass substrate coated by a layer of SiO2. SiO2 layers were obtained by sol-gel method. In another choice, silver nanoparticles were added to the SiO2 layer under the TiO2 coatings. Samples were characterized by GXRD, UV-Vis and FTIR spectroscopy, TEM and spectral ellipsometry. Photocatalytic properties were studied through the degradation of methyl orange (MO) in aqueous solution. Samples with silver in the SiO2 layer were the most efficient photocatalysts followed by Ag-doped TiO2 coatings. UV-Vis spectroscopy measurements showed that the onset of absorption of Ag-doped TiO2 coatings shifted to lower energies than TiO2 layers. This fact shows a decrease of the band gap energy bcause of silver nanoparticles create trap levels between the conduction and valence band of TiO2. Thus, increase the concentration of pairs electron-holes by irradiation with light UV-Visible. Photoluminescence measurements showed that silver nanoparticles contribute to separate the electron-holes pairs and then avoid recombination and increase the concentration of these reactive species. The antimicrobial effect was carried out against Escherichia Coli, Staphylococcus Aureus and Listeria monocytogenes. Coatings doped with Ag were found to be more antimicrobially active than the undoped coatings. There is no appreciable difference between coatings doped in SiO2 or TiO2 layer. Measurements of Ag+ concentration in an aqueous medium in contact with doped coatings showed that silver ion release contribute to the bactericide effect. Thus, we obtained Ag-doped materials with improved photocatalytic and bactericide properties.