Nina G. Kostova

Cystine-capped CdSe@ZnS nanocomposites: mechanochemical synthesis, properties, and the role of capping agent

Cystine-capped CdSe@ZnS nanocomposites were synthesized mechanochemically with the aim to prepare a material which could be used in medicine for biosensing applications. Although synthesized CdSe@ZnS nanocomposites were capped with l-cysteine, cystine was formed from l-cysteine during the milling process. It was proven that water plays the key role in this oxidative transformation. The novel material was characterized by the complex of physico-chemical methods (FTIR, XPS, SEM, EDX, surface area measurements) and CHNS analysis. The leakage of Cd2+ and Zn2+ ions into physiological solution was also studied.

Thiophene conversion and ethanol oxidation on SiO2-supported 12-PMoV-mixed heteropoly compounds

Abstract Surface properties of supported MoV heteropoly compounds and their activities in hydrodesulfurization of thiophene and oxidation of ethanol were studied. Vanadium incorporated into the phosphomolybdic acid anion increased extent of oxidative dehydrogenation of ethanol to acetaldehyde, whereas the catalyst with (VO)2+ increased complete ethanol oxidation to CO2. The catalysts with (VO)2+ or one V atom in the anion showed an increase in HDS activity. Vanadium in anion of phosphomolybdic acid also increased hydrogenation ability. Acidic sites of medium strength were proved to be the most suitable for ethanol oxidation. Such explicit dependence of thiophene hydrodesulfurization on any type of acidic sites was not confirmed. Activity order of supported MoV heteropoly compounds in HDS of thiophene correlated well with the amount of hydrogen consumed during TPR.

CdS/ZnS nanocomposites: from mechanochemical synthesis to cytotoxicity issues.

CdS/ZnS nanocomposites have been prepared by a two-step solid-state mechanochemical synthesis. CdS has been prepared from cadmium acetate and sodium sulfide precursors in the first step. The obtained cubic CdS (hawleyite, JCPDS 00-010-0454) was then mixed in the second step with the cubic ZnS (sphalerite, JCPDS 00-005-0566) synthesized mechanochemically from the analogous precursors. The crystallite sizes of the new type CdS/ZnS nanocomposite, calculated based on the XRD data, were 3-4 nm for both phases. The synthesized nanoparticles have been further characterized by high-resolution transmission electron microscopy (HRTEM) and micro-photoluminescence (μPL) spectroscopy. The PL emission peaks in the PL spectra are attributed to the recombination of holes/electrons in the nanocomposites occurring in depth associated with Cd, Zn vacancies and S interstitials. Their photocatalytic activity was also measured. In the photocatalytic activity tests to decolorize Methyl Orange dye aqueous solution, the process is faster and its effectivity is higher when using CdS/ZnS nanocomposite, compared to single phase CdS. Very low cytotoxic activity (high viability) of the cancer cell lines (selected as models of living cells) has been evidenced for CdS/ZnS in comparison with CdS alone. This fact is in a close relationship with Cd(II) ions dissolution tested in a physiological solution. The concentration of cadmium dissolved from CdS/ZnS nanocomposites with variable Cd:Zn ratio was 2.5-5.0 μg.mL(-1), whereas the concentration for pure CdS was much higher - 53 μg.ml(-1). The presence of ZnS in the nanocrystalline composite strongly reduced the release of cadmium into the physiological solution, which simulated the environment in the human body. The obtained CdS/ZnS quantum dots can serve as labeling media and co-agents in future anti-cancer drugs, because of their potential in theranostic applications.

Interaction of hydrogen sulfide with molybdophosphoric heteropolyacid

The effect of hydrogen sulfide on P−12Mo heteropolyacid has been studied using ESR, IR spectroscopic and thermal analysis methods. It has been established that hydrogen sulfide can be chemisorbed like water and no entering of sulfur into the anion structure takes place.AbstractС помощью методов ЭПР, ИКС и ТА исследовано воздействие сероводорода на P−12Mo гетерополикислоту. Показано, что сероводород может хемосорбироваться аналогично воде. Вхождение серы в структуру аниона не происходит.

Characterization of silica-supported molybdenum catalysts by ESR, XPS and thiophene hydrodesulfurization

Two Mo/SiO2 samples have been prepared by impregnation of silica gel with aqueous solution of molybdophosphoric heteropoly acid or ammonium heptamolybdate. The catalysts were studied by ESR and IR spectroscopy, X-ray diffraction, and XPS. Their activity was measured in the reaction of thiophene hydrodesulfurization. The silica-supported P−Mo heteropoly acid, with a preserved Keggin structure of the heteropoly anion and sulfided by H2S, exhibited two times higher steady conversion in comparison with ammonium heptamolybdate supported on silica at pH=11 and calcined and sulfided at 500°C.

State of cobalt and molybdenum in cobalt-molybdenum-containing zeolites

NaY and CaHY zeolites containing 7 wt.% Mo and 0.7 wt.% Co have been studied by means of IR and diffuse reflectance spectroscopy (DRS). It is shown that ammonium heptamolybdate (AHM) interacts with the zeolite forming a silicon molybdenum heteropoly complex (SiMo HPC). In contrast to NaY, along with SiMo HPC, MoO3 is formed on CaHY after calcining.AbstractNaY и CaY цеолиты, содержащие 7 вес.% Mo и 0,7 вес.% Co, были исследованы с помощью ИК спектроскопии и диффузного отражения. Показано, что гептамолибдат аммония взаимодействует с цеолитом, образуя гетерополикомплекс кремния с молибденом (SiMo HPC). В противоположность цеолитам NaY, на цеолитах CaHY после обжига наряду с SiMo HPC образуется также MoO3.

Synthesis and properties of hydrodesulfurization catalysts, III. Support effect on the catalytic activity of Co−Mo−Al2O3 catalysts

By means of DTA, reflectanc spectra and measurement of catalytic activity in thiophene hydrogenolysis, the effect of support (aluminium hydroxide and oxide) as well as of the order of introduction of molybdenum and cobalt compounds on the structure and catalytic surface of Co−Mo−Al2O3 catalysts is shown.AbstractС помощью ДТА, спектров отражения и измерений каталитической активности в гидрогенолизе тиофена был подтвержден эффект носителя (гидроокиси и окиси алюминия) и порядка введения соединений модибдена и кобальта на структуру, а также влияние каталитической поверхности катализаторов Co−Mo−Al2O3.