Use of titanium dioxide (TiO2) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing.

The aim of this work was to study the photocatalytic activity of titanium dioxide (TiO(2)) against Listeria monocytogenes bacterial biofilm. Different TiO(2) nanostructured thin films were deposited on surfaces such as stainless steel and glass using the doctor-blade technique. All the surfaces were placed in test tubes containing Brain Heart (BH) broth and inoculated with L. monocytogenes. Test tubes were then incubated for 10 days at 16°C in order to allow biofilm development. After biofilm formation, the surfaces were illuminated by ultraviolet A light (UVA; wavelength of 315-400 nm). The quantification of biofilms was performed using the bead vortexing method, followed by agar plating and/or by conductance measurements (via the metabolic activity of biofilm cells). The presence of the TiO(2) nanoparticles resulted in a fastest log-reduction of bacterial biofilm compared to the control test. The biofilm of L. monocytogenes for the glass nanoparticle 1 (glass surface modified by 16% w/v TiO(2)) was found to have decreased by 3 log CFU/cm(2) after 90 min irradiation by UVA. The use of TiO(2) nanostructured photocatalysts as alternative means of disinfecting contaminated surfaces presents an intriguing case, which by further development may provide potent disinfecting solutions. Surface modification using nanostructured titania and UV irradiation is an innovative combination to enhance food safety and economizing time and money.

Photo-induced effects on self-organized TiO2 nanotube arrays: the influence of surface morphology.

Self-organized TiO(2) nanotubes with packed, vertically aligned morphology and different lateral characteristics were grown on Ti metal substrates by controlled electrochemical anodization in phosphate/HF and ethylene glycol/HF electrolytes. The wetting, photo-induced superhydrophilicity, and photocatalytic activity of the nanotubular materials were investigated under ultraviolet irradiation. The photoactivity of the TiO(2) nanotube arrays was analysed in terms of their morphological characteristics that were determined by means of scanning electron microscopy and atomic force microscopy in conjunction with geometrical modelling. The wetting and the UV-induced superhydrophilicity could be accordingly modelled by the Cassie-Baxter mode arising from the large scale roughness of the nanotubular arrays in combination with the Wenzel mode due to the small scale roughness induced by ridges at the outer tube surface. The photocatalytic activity of the TiO(2) nanotube arrays was further found to correlate quantitatively with the variation of the geometric roughness factor, verifying the strong impact of morphology on the photo-induced properties of the vertically oriented TiO(2) tubular architecture.

Dye-sensitized solar cells based on thick highly ordered TiO(2) nanotubes produced by controlled anodic oxidation in non-aqueous electrolytic media.

Dye-sensitized solar cells (DSSCs) were prepared using TiO(2) nanotubes, grown by controlled Ti anodic oxidation in non-aqueous media. Smooth, vertically oriented TiO(2) nanotube arrays, presenting a high degree of self-organization and a length of 20 µm, have been grown using ethylene glycol electrolyte containing HF. As-grown nanotubes exhibit an amorphous structure, which transforms to the anatase TiO(2) crystalline phase upon post-annealing in air at 450 °C. Atomic force microscopy (AFM) revealed the porous morphology together with high roughness and fractality of the surface. The annealed tubes were sensitized by the standard N719 ruthenium dye and the adsorption was characterized using resonance micro-Raman spectroscopy and adsorption-desorption measurements. The sensitized tubes were further used as active photoelectrodes after incorporation in sandwich-type DSSCs using both liquid and solidified electrolytes. The efficiencies obtained under air mass (AM) 1.5 conditions, using a back-side illumination geometry, were very promising: 0.85% using a composite polymer redox electrolyte, while the efficiency was further increased up to 1.65% using a liquid electrolyte.