Facile Synthesis of TiO2 Nanoparticles of Different Crystalline Phases and Evaluation of Their Antibacterial Effect Under Dark Conditions Against E. coli

Abstract

In this paper we report the antibacterial activity in the absence of UV–Vis irradiation of TiO2 nanoparticles, in amorphous, anatase and rutile phases, obtained by the sol–gel process, on Escherichia coli strains. The synthesized TiO2 powders were characterized using X-ray diffraction (XRD), IR spectroscopy and UV–Vis absorption, as well as scanning and transmission electron microscopies. The XRD results showed that the solids were amorphous up to a temperature of 350 °C and that when subjected to heat treatments of higher temperatures, anatase crystalline phases were obtained, at 450 °C, and rutile type at temperatures higher than 770 °C, with a sub-micron particle size (< 1 μm) and varying morphology. The inactivating effect on bacteria of synthesized TiO2 was analyzed by recording the effect of its presence on bacterial strains of E. coli. To this end, the synthesized TiO2 in its amorphous (am-TiO2), anatase (a-TiO2) or rutile (r-TiO2) phases, at different concentrations, was incorporated into the E. coli cultures, placing aluminum foil over the strains to simulate darkness. Although all the phases of the TiO2 synthesized present reasonable antibacterial activity, the highest efficiency is seen in the cultures treated with r-TiO2.