ABSTRACT
Thermally stable Au single-atoms supported by monolayered CuO grown at Cu(110) have been successfully prepared. The charge transfer from the CuO support to single Au atoms is confirmed to play a key role in tuning the activity for CO oxidation. Initially, the negatively charged Au single-atom is active for CO oxidation with its adjacent lattice O atom depleted to generate an O vacancy in the CuO monolayer. Afterward, the Au single-atom is neutralized, preventing further CO reaction. The produced O vacancy can be healed by exposure to O2 at 400 K and accordingly the reaction activity is restored.
ABSTRACT
Photoinduced water dissociation on rutile-TiO2 was investigated using various methods. Experimental results reveal that the water dissociation occurs via transferring an H atom to a bridge bonded oxygen site and ejecting an OH radical to the gas phase during irradiation. The reaction is strongly suppressed as the water coverage increases. Further scanning tunneling microscopy study demonstrates that hydrogen bonds between water molecules have a dramatic effect on the reaction. Interestingly, a single hydrogen bond in water dimer enhances the water dissociation reaction, while one-dimensional hydrogen bonds in water chains inhibit the reaction. Density functional theory calculations indicate that the effect of hydrogen bonds on the OH dissociation energy is likely the origin of this remarkable behavior. The results suggest that avoiding a strong hydrogen bond network between water molecules is crucial for water splitting.
ABSTRACT
Implant-related infection is one of the most common and serious complications associated with biomedical implantation. To prevent bacterial adhesion, a series of porous TiO2 coatings with different concentrations of silver (designated as M0, M1, M2 and M3) were prepared on pure titanium substrates by a duplex-treatment technique combining magnetron sputtering with micro-arc oxidation. All coatings are porous with pore size less than 5 µm and the concentrations of silver in the M0, M1, M2 and M3 are 0, 0.95, 1.36 and 1.93 wt.%, respectively. Silver is found to be distributed throughout the thickness of the coatings by scanning electron microscopy. The release of silver from the TiO2 coatings was confirmed by an inductively-coupled plasma mass spectroscopy. The antibacterial effects of these coatings were tested against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli), and the cytotoxicity was evaluated using the mouse pre-osteoblast cells. The results indicate that the antibacterial activities of TiO2 coatings are greatly improved due to the incorporation of silver. No cytotoxic effect is found for the M1 surfaces from the observation of pre-osteoblast cell by MTT assay and fluorescence microscopy. Although the M2 and M3 coatings appeared to be toxic for pre-osteoblast cells after 1 day in culture, the cell viability on M2 and M3 surfaces was greatly raised after culturing for 2 days. Our results suggested that the TiO2 coatings incorporated with an optimum amount of silver can possess excellent antibacterial activities without cytotoxic effect, which has promising applications in biomedical devices.
