Supported TiO2 films deposited at different energies: Implications of the surface compactness on the catalytic kinetics
Insight is provided in this study for the effect of the TiO2film densification/compactness on polyethy-lene (PE-TiO2) by sputtering TiO2at two very different energy levels. Uniform, adhesive low energy filmswere prepared by direct current magnetron sputtering (DCMS) and compared with films sputtered athigh energy levels by high power impulse magnetron sputtering (HIPIMS). Nano-particulate TiO2filmssputtered by HPIMS presented sizes of ∼10.2 nm compared to films sputtered by DCMS with TiO2sizesof ∼16.5 nm as determined by X-ray diffraction (XRD). The E. coli inactivation kinetics was three timesfaster for the samples sputtered by HIPIMS compared to their DCMS counterparts. This is an unexpectedfinding since the DCMS presenting larger TiO2sized nanoparticles released a higher amount of Ti-ionscompared 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 theless compact TiO2sputtered by DCMS. The faster bacterial inactivation kinetics observed by the HIPIMSsputtered samples can be understood in terms of the complete of Ti4+/Ti3+redox conversion during bacte-rial inactivation detected by X-ray photo-electron spectroscopy (XPS) compared to the smaller Ti4+/Ti3+effect observed in the DCMS-samples. A higher optical density was detected for the HIPIMS sputteredsamples by diffuse reflectance spectroscopy (DRS). Evidence is presented for the shift in surface potentialand local pH during bacterial inactivation under aerobic and anaerobic conditions. A reaction mechanismis suggested based on the findings described in this study. The sputtered films present the potential tohinder biofilm formation on flexible thin polymers/textiles widely used in hospitals and health facilities.