Dynamics of photogenerated charge carriers in TiO2 /MoO3, TiO2 /WO3 and TiO2 /V2O5 photocatalysts with mosaic structure

Titania is a widely used photocatalytic material possessing such advantages as low cost and high reactivity under the ultraviolet light illumination. However, the fast recombination of photoexcited charge carriers limits its application. Herein, we have synthesized original nanomaterials with mosaic structures that exhibited well-defined heterojunctions and new properties. Using SEM, XRD, EPR spectroscopy, photocatalytic measurements, and photoinduced pathphysiological activity of these photocatalysts, we studied the processes of charge carrier accumulation in TiO2 /MoO3, TiO2 /WO3, and TiO2 /V2 O5 under in situ UV illumination with emphasis on the charge exchange between energy levels of these nanosized semiconductors. It is shown that the accumulation of photoinduced charges occurs in two forms (i) filled electron traps corresponding to Ti4+ /Ti3+ levels and (ii) Mo5+ centers, both forms contributing to the photoinduced biocide activity of the samples. This work demonstrates that light exposure of heterostructure photocatalysts with mosaic surfaces produces different types of charge-trapping centers capable of interacting with molecular oxygen yielding peroxo species, which provide long-life light-induced ”self-cleaning” behavior. Such photoaccumulating materials open new opportunities in developing light-driven self-sterilization structures exhibiting a prolonged bactericidal effect up to 10 h after stopping light exposure. © 2020 by the authors. Licensee MDPI, Basel, Switzerland

Study of the Effect of Squalene Epoxidase Activity on Squalene Biosynthesis by Yeast Saccharomyces Cerevisiae VGSh-2

The researchers of this study investigated the biosynthesis of squalene by the yeast S. cerevisiae VGSH-2 through the activity of squalene epoxidase, which is a key enzyme in the conversion of squalene to ergosterol. It has been established that under aerobic conditions the antimycotic drug terbinafine promotes the switching of ergosterol formation to squalene synthesis. This switch occurs through specific inhibition of the squalene epoxidase of the yeast S. cerevisiae VGSH-2, thus increasing the biosynthetic ability of the yeast towards squalene. According to the results of this study, the optimal concentration of terbinofine in the nutrient medium was 0.3 μmol / cm3 . This concentration led to a 5-fold decrease in squalene epoxidase activity and a 7-8 times increase in squalene synthesis. The results obtained can be used to develop a competitive technology for the industrial production of squalene by microbial synthesis. Keywords: squalene, yeast, biosynthesis, inhibition of activity, terbinafine, squalene epoxidase, Saccharomices cerevisiae VGSH-

Effect of Aluminum Ion Irradiation on Chemical and Phase Composition of Surface Layers of Rolled AISI 321 Stainless Steel

Commercial rolled AISI 321 stainless steel samples were irradiated with Al+ ions with an energy of 80 keV and fluence of 1017 ion/cm2. The effect of Al implantation on the chemical and phase composition of the steel surface layer was studied by X-ray electron spectroscopy and grazing beam mode of X-ray diffraction analysis. A thin surface layer down to a depth of 30 nm after Al+ ions implantation consists mainly of metal oxides. In the near-surface layers of 5 nm in depth, a noticeable depletion in chromium and nickel was observed. A surface layer (up to 0.5 µm) of non-irradiated steel, in addition to the f.c.c. austenite γ-phase, consists of up to 20 vol% of the b.c.c. α′-phase, which formed at rolling as a result of mechanical deformation. Al implantation results in the significant increase in the α′-phase amount in the surface layer at a depth up to 2 µm. It is indicated that the observed γ → α′ transformation at ion irradiation proceeds predominantly as a result of the effect of post-cascade shock waves, but not as a result of the surface layer chemical composition changes