No abstract

Titania (TiO2)-based nanocomposites subjected to light excitation are remarkably effective in eliciting microbial death. However, the mechanism by which these materials induce microbial death and the effects that they have on microbes are poorly understood. Here, we assess the low dose radical-mediated TiO2 photocatalytic action of such nanocomposites and evaluate the genome/proteome-wide expression profiles of Pseudomonas aeruginosa PAO1 cells after two minutes of intervention. The results indicate that the impact on the gene-wide flux distribution and metabolism is moderate in the analysed time span. Rather, the photocatalytic action triggers the decreased expression of a large array of genes/proteins specific for regulatory, signalling and growth functions in parallel with subsequent selective effects on ion homeostasis, coenzyme-independent respiration and cell wall structure. The present work provides the first solid foundation for the biocidal action of titania and may have an impact on the design of highly active photobiocidal nanomaterials.

The structural and electronic properties of Ce 1-x Ni x O 2-y nanosystems prepared by a reverse microemulsion method were characterized with synchrotron-based X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and density functional calculations. The Ce 1-x Ni x O 2-y systems adopt a lattice with a fluoritetype structure with an acute local order where Ni displays a strongly distorted (oxygen) nearest-neighbor coordination and the presence of Ni atoms as first cation distances, pointing to the existence of Ni-O-Ni entities embedded into the ceria lattice. A Ni T Ce exchange within the CeO 2 leads to a charge redistribution and the appearance of O vacancies. The Ni-O bonds in Ce 1-x Ni x O 2-y are more difficult to reduce than the bonds in pure NiO. The specific structural configuration of Ni inside the mixed-metal oxide leads to a unique catalyst with a high activity for the water gas shift (CO + H 2 O f H 2 + CO 2 ) reaction and a simultaneous reduction of the methanation activity of nickel. Characterization results indicate that small particles of metallic Ni at the interface position of a ceria network may be the key for high WGS activity and that the formate-carbonate route is operative for the production of hydrogen.

The role of interface contact between two oxides, CeO2 and TiO2, for the photocatalytic elimination of toluene is examined in a series of samples with variable quantities of ceria. Samples having ceria contents in the 1 to 10 mol % range improve significantly, exhibiting up to 3.5 times the activity of the bare nano-TiO2 catalyst. To interpret the photocatalytic behavior, this contribution develops a novel spectro-kinetic approach where a joined analysis of the kinetics of the reaction and the fate of charge charriers is merged with the mathematical modeling of the light–catalyst interaction at the photoreactor. This produces a self-consistent approach that simultaneously validates the kinetic model and interprets the activity on rigorous bases. The study is completed with a multitechnique examination of the solids using X-ray diffraction and electron paramagnetic resonance, UV–vis, and X-ray photoelectron spectroscopies as well as high-resolution transmission electron microscopy. The results provide quantitative evidence that the oxide–oxide contact controls the photoactivity through the number of hole-related species available at the surface of the composite materials and that this number is in turn related to the stabilization of reduced Ce species present at the Ce–Ti interface.