Supported TiO2 films deposited at different energies: Implications of the surface compactness on the catalytic kinetics.

Abstract

a b s t r a c tInsight is provided in this study for the effect of the TiO 2 film densification/compactness on polyethylene (PE-TiO 2 ) by sputtering TiO 2 at two very different energy levels. Uniform, adhesive low energy films were prepared by direct current magnetron sputtering (DCMS) and compared with films sputtered at high energy levels by high power impulse magnetron sputtering (HIPIMS). Nano-particulate TiO 2 films sputtered by HPIMS presented sizes of ∼10.2 nm compared to films sputtered by DCMS with TiO 2 sizes of ∼16.5 nm as determined by X-ray diffraction (XRD). The E. coli inactivation kinetics was three times faster for the samples sputtered by HIPIMS compared to their DCMS counterparts. This is an unexpected finding since the DCMS presenting larger TiO 2 sized nanoparticles released a higher amount of Ti-ions compared to the HIPIMS samples as monitored by inductively coupled plasma mass-spectrometry (ICP-MS). The Ti-ions released do not seem to react through an oligodynamic effect but diffuse through the less compact TiO 2 sputtered by DCMS. The faster bacterial inactivation kinetics observed by the HIPIMS sputtered samples can be understood in terms of the complete of Ti 4+ /Ti 3+ redox conversion during bacterial inactivation detected by X-ray photo-electron spectroscopy (XPS) compared to the smaller Ti 4+ /Ti 3+ effect observed in the DCMS-samples. A higher optical density was detected for the HIPIMS sputtered samples by diffuse reflectance spectroscopy (DRS). Evidence is presented for the shift in surface potential and local pH during bacterial inactivation under aerobic and anaerobic conditions. A reaction mechanism is suggested based on the findings described in this study. The sputtered films present the potential to hinder biofilm formation on flexible thin polymers/textiles widely used in hospitals and health facilities.

Indoor Light Enhanced Photocatalytic Ultra-Thin Films on Flexible Non-Heat Resistant Substrates Reducing Bacterial Infection Risks

“…The HO • -radicals generation was seen to increase by increasing the temperature from 26 to 50 °C. This increase reveals that the process of HO • generation involves ion-molecule, radical-molecule and ionradical species as recently reported [51][52][53]. For PE-TiO2 HIPIMS samples shown in Figure 4 (traces 3 and 4) show alike trend for the generation of HO • -radicals at 26 and 50 °C respectively.…”

“…It was recently reported by Rtimi et al that E. coli inactivation kinetics was surprisingly three times faster for the samples prepared by HIPIMS compared to their DCMS counterparts [51]. This fast kinetics was not expected since the TiO 2 prepared via DCMS presents larger nanoparticles size.…”

“…This leads to build up n π transitions increasing the absorbing sites on the PE [52]. The higher light absorption of the HIPIMS layers provides the evidence for a dense/compact thin film compared to the more transparent TiO 2 layers prepared by DCMS [51].…”

“…These HO • radicals generation was seen to be dependent of sputtering time and the applied light. More recently, Rtimi et al reported the effect of the applied power/current to the sputtering-target on the HO • -radicals production [51]. The increase in HO • radicals generation is proportional to the fluorescence of the 2-hydroxyterephthalic acid and are seen to increase with irradiation time until it reaches a plateau.…”

Recent Developments in Accelerated Antibacterial Inactivation on 2D Cu-Titania Surfaces under Indoor Visible Light

“…The focus of innovative antibacterial materials is to find composites in colloid form or deposited on surfaces that are able to inactivate bacteria/pathogens within very short times and that have long operational lifetimes (high stability) [1][2][3][4][5]. Biofilms that spread bacteria in hospitals, schools, and public places are the most common and dangerous forms of infection by pathogens: bacteria, fungi, and viruses.…”