ABSTRACT
Yeast Saccharomyces cerevisiae may be regarded as a cost-effective and environmentally friendly biosorbent for complex effluent treatment. The effect of pH, contact time, temperature, and silver concentration on metal removal from silver-containing synthetic effluents using Saccharomyces cerevisiae was examined. The biosorbent before and after biosorption process was analysed using Fourier-transform infrared spectroscopy, scanning electron microscopy, and neutron activation analysis. Maximum removal of silver ions, which constituted 94-99%, was attained at the pH 3.0, contact time 60 min, and temperature 20 °C. High removal of copper, zinc, and nickel ions (63-100%) was obtained at pH 3.0-6.0. The equilibrium results were described using Langmuir and Freundlich isotherm, while pseudo-first-order and pseudo-second-order models were applied to explain the kinetics of the biosorption. The Langmuir isotherm model and the pseudo-second-order model fitted better experimental data with maximum adsorption capacity in the range of 43.6-108 mg/g. The negative Gibbs energy values pointed at the feasibility and spontaneous character of the biosorption process. The possible mechanisms of metal ions removal were discussed. Saccharomyces cerevisiae have all necessary characteristics to be applied to the development of the technology of silver-containing effluents treatment.
ABSTRACT
The paper considers the new effects of the nanoscale state of matter, which open up prospects for the development of electronic devices using new physical principles. The contacts of chemically homogeneous nanoparticles of yttrium-stabilized zirconium oxide (ZrO2x mol% Y2O3, x = 0, 3, 4, 8; YSZ) with different sizes of 7.5 nm and 9 nm; 7.5 nm and 11 nm; and 7.5 nm and 14 nm, respectively, was studied on direct current using nanostructured objects in the form of compacts obtained by high-hydrostatic pressure (HP-compacts of 300MPa). A unique size effect of the nonlinear (rectifying-type contact) dependence of the electrical properties (in the region U < 2.5 V, I ≤ 2.7 mA) of the contact of different-sized YSZ nanoparticles of the same chemical composition is revealed, which indicates the possibility of creating semiconductor structures of a new type (homogeneous electronics). The electronic structure of the near-surface regions of nanoparticles of studied oxide materials and the possibility of obtaining specifically rectifying properties of the contacts were studied theoretically. Models of surface states of the Tamm-type are constructed considering the Coulomb long-range action. The discovered energy variance and its dependence on the curvature of the surface of nanoparticles made it possible to study the conditions for the formation of a contact potential difference in cases of nanoparticles of the same radius (synergistic effect), different radii (doped and undoped variants), as well as to discover the possibility of describing a group of powder particles within the Anderson model. The determined effect makes it possible to solve the problem of diffusion instability of semiconductor heterojunctions and opens up prospects for creating electronic devices with a fundamentally new level of properties for use in various fields of the economy and breakthrough critical technologies.
ABSTRACT
The radioactivity concentrations of 226Ra, 232Th and 40K natural radionuclides in Lao Portland cement samples were measured using a gamma-spectrometry with a HPGe detector. The activity concentrations were found to vary from 28.32 ± 2.23 to 65.50 ± 2.83 Bq kg-1 with a mean value of 41.12 ± 2.44 Bq kg-1 for 226Ra; from 7.25 ± 2.00 to 44.01 ± 2.45 Bq kg-1 with a mean of 16.60 ± 2.37 Bq kg-1 for 232Th and from 49.19 ± 4.27 to 196.74 ± 4.75 Bq kg-1 with a mean of 141.48 ± 4.50 Bq kg-1 for 40K, respectively. The radiological parameters were estimated to assess the potential radiological hazard including radium equivalent activity, total external absorbed dose rate in outdoor air at 1 m above the earth's surface, the annual effective dose, the gamma and alpha-indices were calculated using the activity concentrations of 226Ra, 232Th and 40K. The results obtained in this study show no significant radiological hazards arising from using Lao Portland cement for building construction.
