Self-assembly processes in low-concentration hydrogels based on the amino acid l-cysteine, silver nitrate, and the polysaccharide chitosan (CS) with the addition of various electrolytes, namely, copper sulfate and sodium sulfate, which function as gelation initiators, were studied. Vibrational viscometry, UV and FTIR spectroscopy, as well as scanning electron microscopy were used to determine that the electrolyte cation that initiates gelation affects the structural and mechanical properties of hydrogels based on a cysteine-silver solution (CSS). Unlike NaI cations, the CuII cations act as a linker between the zwitterions of silver mercaptide (cysteinate), that is, the structural elements of the CSS cluster chains, via coordination with carboxylate and amino groups; additionally, coordination processes between CuII and chitosan in CSS-CS-CuSO4 systems are also possible, improving the mechanical properties of the hydrogels, while reducing their stability over time.
Magnesium chloride and bromide hexahydrates in combination with readily available amines were tested as catalysts for the addition of CO2 to oxiranes affording cyclic carbonates. The system based on MgBr2 & centerdot;6H2O and pyridine or 1,1,3,3-tetramethylguanidine can effectively catalyze this process.
Nanocomposites SnO2/SiO2 ([Si]/[Si+Sn] = 15 at.%) and WO3/SiO2 ([Si]/[Si+W] = 5, 15, and 25 at.%) were synthesized by solvothermal treatment of a SiO2 center dot xH2O sol in the presence of dried SnO2 center dot xH2O and WO3 center dot H2O gels, respectively, followed by high-temperature (600 degrees C) annealing. During the formation of the SnO2/SiO2 nanocomposites, the decrease in the growth rate of the SnO2 crystallites occurring due to the Zener-Smith effect is significantly more pronounced than upon the modification of WO3. A comparative analysis was performed for the first time, demonstrating that the choice of the semiconductor oxide precursor in the synthesis of composites with a stabilized small crystallite size and a high specific surface area is of principal importance. Compared to SnO2 and WO3 binary oxides, the SnO2/SiO2 and WO3/SiO2 nanocomposites exhibit an enhanced sensor response in the detection of 2 ppm of benzene in dry air (relative humidity RH = 0%). The SnO2/SiO2 nanocomposite maintains a high sensor response to benzene even when the relative humidity increases to RH = 30-90%.
Bentonite clays are traditionally used as the main mineral component of engineered safety barriers for radioactive waste disposal, however, their sorption capacity is limited for a number of highly mobile radionuclides, including SrII, NpV, and UVI. This work investigated the sorption properties of synthetic delta-MnO2, a structural analog of natural birnessite, with respect to SrII, NpV, and UVI over a wide pH range. Despite the smaller specific surface area and cation exchange capacity compared to bentonite clay, delta-MnO2 exhibited significantly higher distribution coefficients for SrII and NpV, up to similar to 106 and similar to 104 mL g-1, respectively. The obtained results confirm the high efficiency of delta-MnO2 as a functional additive for modification of the sorption properties of bentonite clay-based materials and increase in the retention of highly mobile radionuclides in engineered safety barriers.
The compounds SrLnCuSe3 (Ln = Sm, Er, Yb) and EuErCuSe3 were obtained from metal selenides synthesized from simple substances. Measurements of electrical conductivity and Seebeck coefficient were carried out in the temperature range of 310-420 K for ceramic samples pressed at 673 K. All the obtained compounds are p-type semiconductors. For complex strontium selenides, electrical resistivity decreases with increasing temperature: rho = 710-380 Omega cm for SrSmCuSe3 and rho = 1.4-1.3 Omega cm for SrYbCuSe3, while in the case of the EuErCuSe3 phase, electrical resistivity increases with increasing temperature. The Seebeck coefficients increase with temperature in the ranges: S = 160-225 & micro;V K-1 for SrSmCuSe3 and S = 12-26 & micro;V K-1 for SrYbCuSe3. The widths of the thermal band gap E g for SrLnCuSe3 (Ln = Sm, Er, Yb) are equal to 0.26, 0.07, and 0.06 eV, respectively. The widths of the optical band gap for direct and indirect electronic transitions correspond to 2.12, 3.84 eV and 1.7, 1.05 eV for SrSmCuSe3 as well as 1.4, 1.68 eV and 0.545 eV for SrYbCuSe3. The results indicate a strong dispersion of the bottom of the conduction band. The temperatures and enthalpies of incongruent melting of the compounds SrSmCuSe3 (T = 1485 K, Delta H = 23.2 J g-1) and SrYbCuSe3 (T = 1510 K, Delta H = 20.5 J g-1) were determined.
