The Native Oxide on Titanium Metal as a Conductive Model Substrate for Oxygen Reduction Reaction Studies

Effect of Femtosecond Laser-Irradiated Titanium Plates on Enhanced Antibacterial Activity and Preservation of Bacteriophage Stability

Titanium (Ti) is widely recognized for its exceptional properties and compatibility with medical applications. In our study, we successfully formed laser-induced periodic surface structures (LIPSS) on Ti plates with a periodicity of 520-740 nm and a height range of 150-250 nm. To investigate the morphology and chemical composition of these surfaces, we employed various techniques, including field emission scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Additionally, we utilized a drop-shape analyzer to determine the wetting properties of the surfaces. To evaluate the antibacterial activity, we followed the ISO 22196:2011 standard, utilizing reference bacterial cultures of Gram-positive Staphylococcus aureus (ATCC 25923) and Gram-negative Escherichia coli (ATCC 25922). The results revealed enhanced antibacterial properties against Staphylococcus aureus by more than 99% and Escherichia coli by more than 80% in comparison with non-irradiated Ti. Furthermore, we conducted experiments using the Escherichia coli bacteriophage T4 (ATCC 11303-B4) and the bacterial host Escherichia coli (ATCC 11303) to investigate the impact of Ti plates on the stability of the bacteriophage. Overall, our findings highlight the potential of LIPSS on Ti plates for achieving enhanced antibacterial activity against common bacterial strains while maintaining the stability of bacteriophages.

From Bulk to Atoms: The Influence of Particle and Cluster Size on the Hydrogen Evolution Reaction

To investigate the influence of particle size in terms of electrocatalysis for the hydrogen evolution reaction (HER), small Pt n species with n = 1 , 10 , 13 $n=1,10,13$ atoms and nanoparticles are deposited onto native titanium dioxide. These species are compared to the bare support as well as to bulk platinum with respect to the catalytic activity. Photoelectron spectroscopy showed Pt4f core-level shifts to higher binding energies with decreasing cluster size. In addition, the various species contribute significant density of states into the valence band gap of TiO2, thereby with larger particle size, the resulting band gap narrows. For nanoparticles, metal-like behaviour was already observed. Electrochemical measurements in 0.1 M H2SO4 showed the highest overall catalytic activity for bulk platinum and large Pt nanoparticles. A different assertion is obtained when the activities are related to the mass of the catalyst used, indicating that clusters with a size of about ten atoms seem to be most active. In comparison with the results from photoelectron spectroscopy regarding the electronic structure, no clear correlation to the catalytic activity was found. In terms of degradation induced due to the electrochemical treatment, the cluster samples showed no sintering effects, but instead, some detachment took place.