Vambola Kisand

Colorimetric gas sensing is demonstrated by thin films based on ultrasmall TiO2 nanoparticles (NPs) on Si substrates. The NPs are bound into the film by p-toluenesulfonic acid (PTSA) and the film is made to absorb volatile organic compounds (VOCs). Since the color of the sensing element depends on the interference of reflected light from the surface of the film and from the film/silicon sub-strate interface, colorimetric detection is possible by the varying thickness of the NP-based film. Indeed, VOC absorption causes significant swelling of the film. Thus, the optical path length is increased, interference wavelengths are shifted and the refractive index of the film is decreased. This causes a change of color of the sensor element visible by the naked eye. The color response is rapid and changes reversibly within seconds of exposure. The sensing element is extremely simple and cheap, and can be fabricated by common coating processes.

ABSTRACT The present work reports the co-precipitation synthesis and photocatalytic activity of MFe2O4 (M = Ni, Zn, Co, Cu, Mg) nanopowders. To compare their properties, all the powders were synthesized under similar synthesis conditions. Their structures and properties were determined by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis diffuse reflectance spectra, nitrogen adsorption–desorption, and vibrating sample magnetometry. The results revealed the formation of single-phase spinel-structure magnetic nanoparticles with particle size 2O4 photocatalyst reached ~70 %.

The concept of nanotechnologies is based on size-dependent properties of particles in the 1-100 nm range. However, the relation between the particle size and biological effects is still unclear. The aim of the current paper was to generate and analyse a homogenous set of experimental toxicity data on Ag nanoparticles (Ag NPs) of similar coating (citrate) but of 5 different primary sizes (10, 20, 40, 60 and 80 nm) to different types of organisms/cells commonly used in toxicity assays: bacterial, yeast and algal cells, crustaceans and mammalian cells in vitro. When possible, the assays were conducted in ultrapure water to minimise the effect of medium components on silver speciation. The toxic effects of NPs to different organisms varied about two orders of magnitude, being the lowest (∼0.1 mg Ag/L) for crustaceans and algae and the highest (∼26 mg Ag/L) for mammalian cells. To quantify the role of Ag ions in the toxicity of Ag NPs, we normalized the EC50 values to Ag ions that dissolved from the NPs. The analysis showed that the toxicity of 20-80 nm Ag NPs could fully be explained by released Ag ions whereas 10 nm Ag NPs proved more toxic than predicted. Using E. coli Ag-biosensor, we demonstrated that 10 nm Ag NPs were more bioavailable to E. coli than silver salt (AgNO3). Thus, one may infer that 10 nm Ag NPs had more efficient cell-particle contact resulting in higher intracellular bioavailability of silver than in case of bigger NPs. Although the latter conclusion is initially based on one test organism, it may lead to an explanation for "size-dependent" biological effects of silver NPs. This study, for the first time, investigated the size-dependent toxic effects of a well-characterized library of Ag NPs to several microbial species, protozoans, algae, crustaceans and mammalian cells in vitro.

High-resolution (K3psigmaandpi)-->sigma absorption spectrum of KF in the photon energy range of 18.2-19.4 eV was measured at the new FINEST beamline branch on the I3 beamline on MAX III. The experimental spectrum is presented and interpreted using nonrelativistic ab initio molecular calculations corrected with perturbation theory treatment to account for spin-orbit interaction. Resonant Auger decay recorded at the strongest resonances is also presented and reproduced by theoretical calculations. Also a brief introduction to the FINEST beamline branch is presented.

The emission of free and self-trapped excitons in solid Kr was investigated using luminescence spectroscopy in the vacuum ultraviolet region. The influence of the sample crystal structure and Xe impurity on the shape and location of the self-trapped exciton band was observed directly using samples grown under different conditions from gases with various degrees of purity. For the first time, the luminescence spectra were measured for practically Xe-free solid Kr samples of high structural quality. New high-resolution reflection spectra of solid Kr were measured as well. Due to the good quality of the samples and excellent vacuum conditions, a new member of the exciton series (n = 5) was revealed. On the basis of high-resolution reflection measurements, more accurate values of several parameters concerning excitons in solid Kr were determined.

Valence-exciton luminescence under inner-shell excitation of the rare gas solids Xe, Kr, and Ar has been measured using time-resolved photoluminescence. Two different processes for exciton creation can be distinguished: creation of " prompt " excitons immediately after excitation (within the experimental time resolution), and creation of " delayed " excitons through electron–hole recombination. The decay structure of the exciton emission in the range of inner-shell excitation is characterized by the coexistence of the two processes. Time-resolved excitation spectra near the 2p edge in Ar, the 3d edge in Kr, and the 4d edge in Xe are discussed. The process of prompt exciton creation is strongly enhanced above an excitation threshold at the energy position of the ionization limit of the core state plus the energy of the valence free exciton.

Silver nanoparticles are extensively used in antibacterial applications. However, the mechanisms of their antibacterial action are not yet fully explored. We studied the solubility-driven toxicity of 100 × 6100 nm (mean primary diameter × length) silver nanowires (NWs) to recombinant bioluminescent Escherichia coli as a target representative of enteric pathogens. The bacteria were exposed to silver nanostructures in water to exclude the speciation-driven alterations. Spherical silver nanoparticles (83 nm mean primary size) were used as a control for the effect of NPs shape. Toxicity of both Ag NWs and spheres to E. coli was observed at similar nominal concentrations: the 4h EC50 values, calculated on the basis of inhibition of bacterial bioluminescence, were 0.42 ± 0.06 and 0.68 ± 0.01 mg Ag/L, respectively. Dissolution and bioavailability of Ag from NWs and nanospheres, analyzed with AAS or Ag-sensor bacteria, respectively, suggested that the toxic effects were caused by solubilized Ag + ions. Moreover, the antibacterial activities of Ag NWs suspension and its ultracentrifuged particle-free supernatant were equal. The latter indicated that the toxic effects of ∼80–100 nm Ag nanostructures to Escherichia coli were solely dependent on their dissolution and no shape-induced/related effects were observed. Yet, additional nanospecific effects could come into play in case of smaller nanosilver particles.

Impurity core-valence luminescence (CVL) spectra arising under selective VUV excitation of highest-lying 5pCs core states in K 1-xCsxCl and Rb1-xCsxCl mixed crystals has been studied in a wide temperature range (7 to 330 K). The single-peaked emission band at 4.5 eV is revealed to demonstrate significant thermal broadening caused by phonon-assisted lattice-relaxation effects in vicinity of impurity core holes. A model of localized emission centres is shown to account reasonably well for the experimental observations. The influence of both concentration and lattice-relaxation effect on the emission spectrum shape in the high-and low-energy regions is shortly discussed.