Abstract
Photocatalytic antibacterial sol-gel coated substrates have been reported to kill bacteria under light or in the dark. These coatings showed non-uniform distribution, poor adhesion to the substrate and short effective lifetime as antibacterial surfaces. These serious limitations to the performance/stability retard the potential application of antibacterial films on a wide range of surfaces in hospital facilities and public places. Here, the preparation, testing and performance of flexible ultra-thin films prepared by direct current magnetron sputtering (DCMS) at different energies are reviewed. This review reports the recent advancements in the preparation of highly adhesive photocatalytic coatings prepared by up to date sputtering technology: High Power Impulse Magnetron Sputtering (HIPIMS). These latter films demonstrated an accelerated antibacterial capability compared to thicker films prepared by DCMS leading to materials saving. Nanoparticulates of Ti and Cu have been shown during the last decades to possess high oxidative redox potentials leading to bacterial inactivation kinetics in the minute range. In the case of TiO2CuOx films, the kinetics of abatement of Escherichia coli (E. coli) and methicillin resistant Staphylococcus aureus (MRSA) were enhanced under indoor visible light and were perceived to occur within few minutes. Oligodynamic effect was seen to be responsible for bacterial inactivation by the small amount of released material in the dark and/or under light as detected by inductively-coupled plasma mass spectrometry (ICP-MS). The spectral absorbance (detected by Diffuse Reflectance Spectroscopy (DRS)) was also seen to slightly shift to the visible region based on the preparation method.
Highlights
Hospital acquired infection (HAI) is a topic of increasing attention due to the increasing number of incidents reported at the national or international levels
Controversial mechanisms are reported on the interaction of CuOx, TiO2 and CuOx -TiO2 with bacterial cells
Spectral shift to the visible region enlarging the light absorption of TiO2 as a function bacterial cells
Summary
Hospital acquired infection (HAI) is a topic of increasing attention due to the increasing number of incidents reported at the national or international levels. Many approaches were adopted to try to reduce the risks of infections in hospital facilities, schools and public places The majority of these approaches were shortcut due to their short operational time or the development of bacterial resistance to their active ingredients. During the last five decades, antibacterial Ag-colloids have been extensively studied describing the antibacterial activity of Ag-impregnated textiles [15,16] These colloidal/sol-gel preparations are not mechanically stable, non-reproducible, show low uniformity and tiny adhesion to the substrate [17]. Film coatings by magnetron sputtering (a PVD technique) avoid the high temperatures needed in CVD to decompose the precursors. The drawbacks of the CVD deposition method are: (i) the high investment costs; (ii) the high temperatures needed to decompose the precursors and limiting the film deposition on non-heat-resistant surfaces (polymers); and (iii) the costly required cooling systems. The strong adhesion of the sputtered atoms/ions/clusters on complex surfaces is due to the higher ions-arrival energies on the surface compared to old method [27]
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