Matthieu Rivallin

Dynamic Mechanisms of the Bactericidal Action of an Al2O3-TiO2-Ag Granular Material on an Escherichia coli Strain.

ABSTRACT The bactericidal activity of an Al2O3-TiO2-Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al2O3-TiO2-Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (105 genomic units · ml−1) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced.

The Reductive Dehydration of Cellulose by Solid/Gas Reaction with TiCl4 at Low Temperature: A Cheap, Simple, and Green Process for Preparing Anatase Nanoplates and TiO2/C Composites

Metal oxides and metal oxide/carbon composites are entering the development of new technologies and should therefore to be prepared by sustainable chemistry processes. Therefore, a new aspect of the reactivity of cellulose is presented through its solid/gas reaction with vapour of titanium(IV) chloride in anhydrous conditions at low temperature (80 °C). This reaction leads to two transformations both for cellulose and titanium(IV) chloride. A reductive dehydration of cellulose is seen at the lowest temperature ever reported and results in the formation of a carbonaceous fibrous solid as the only carbon-containing product. Simultaneously, the in situ generation of water leads to the formation of titanium dioxide with an unexpected nanoplate morphology (ca. 50 nm thickness) and a high photocatalytic activity. We present the evidence showing the evolution of the cellulose and the TiO2 nanostructure formation, along with its photocatalytic activity. This low-temperature process avoids any other reagents and is among the greenest processes for the preparation of anatase and also for TiO2 /carbon composites. The anisotropic morphology of TiO2 questions the role of the cellulose on the growing process of these nanoparticles.