The interrelation of the structure and catalytic properties of hydrogen-reduced iron-ruthenium systems in the ammonia synthesis reaction is studied by X-ray diffraction (XRD), as well as conversion and absorption Mössbauer spectroscopy (MS). It is found that a sample with a metal content of 50Fe/50Ru (wt

Методами рентгеновской дифракции, конверсионной и абсорбционной мессбауэровской спектроскопии изучена взаимосвязь структуры и каталитических свойств восстановленных водородом железорутениевых систем в реакции синтеза аммиака. Найдено, что образец с содержанием металлов 50Fe/50Ru (мас.%) проявляет максимальную каталитическую активность в синтезе аммиака. Показано, что в бинарной системе формируются наноразмерные кластеры интерметаллида Fe–Ru с размером ОКР ~ 11 нм.

Novel biodegradable biocomposites based on poly(3-hydroxybutyrate) nanofibers with embedded iron oxide nanoparticles enriched with 57Fe isotope have been studied by transmission electron microscopy (TEM), Mössbauer spectroscopy, small angle X-ray scattering (SAXS), and macroscopic magnetization techniques.

Методами трансмиссионной электронной микроскопии, мёссбауэровской спектроскопии, динамического светорассеяния, малоуглового рентгеновского рассеяния и измерения макроскопической намагниченности охарактеризованы новые терапевтические, биоразлагаемые, фибриллярные биокомпозиты на основе нановолокон поли‑3-гидроксибутирата, содержащие магнитные наночастицы оксида железа, обогащённого изотопом железа 57 Fe.

The structural, electronic, and magnetic properties of iron oxide nanoparticles encapsulated in hybrid biodegradable therapeutic systems based on poly-3-hydroxybutyrate and chitosan are comprehensively studied using Mössbauer spectroscopy, X-ray diffraction, small-angle X-ray scattering, and macroscopic magnetization measurements. It is shown that iron oxide in concentrations of 4 and 8 wt % in the polymer matrix of magnetically isotropic and magnetoanisotropic systems exists in the form of nanosized (d ≈ 7–8 nm) superparamagnetic clusters. Iron oxide clusters have the structure of a nonstoichiometric inverse spinel, intermediate between polymorphous modifications of Fe3O4 and γ-Fe2O3.

Методами мёссбауэровской спектроскопии и рентгеновской дифракции исследованы структурные, электронные и магнитные свойства наночастиц оксида железа, инкапсулированных в биоразлагаемых терапевтических системах на основе поли-3-гидроксибутирата и хитозана. Показано, что оксид железа с содержанием 4 и 8 мас. % в полимерной матрице существует в двух различных состояниях: в виде наноразмерных (d 7–8 нм) суперпарамагнитных кластеров и “парамагнитных” ионов Fe3+. Установлено, что кластерный нестехиометрический оксид железа имеет структуру обращенной шпинели, промежуточную между Fe3O4 и -Fe2O3 полиморфными модификациями.

The structural, electronic, and magnetic properties of iron oxide nanoparticles encapsulated in biodegradable therapeutic systems based on polyhydroxybutyrate and chitosan have been studied by Mössbauer spectroscopy and X-ray diffraction. It has been shown that, in polymer matrices containing 4 and 8 wt % iron oxide, the latter exists in two different forms: as nanosized ( d ≈ 7–8 nm) superparamagnetic clusters and “paramagnetic” Fe 3+ ions. It has been demonstrated that cluster nonstoichiometric iron oxide has an inverse spinel structure intermediate between the Fe 3 O 4 and γ-Fe 2 O 3 polymorphs.

A complex study of the hydrogen reduction of nanosized iron hydroxide Fe(OH) 3 at 400°C was performed. It was shown that, during the reduction of Fe(OH) 3 to iron metal α-Fe, intermediate compounds such as Fe(OH) 2 , α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH, and FeO are formed along with stable iron oxides α-Fe 2 O 3 , γ-Fe 2 O 3 , and Fe 3 O 4 . A scheme of chemical and structural transformations that occur in the reduction of nanosized Fe(OH) 3 is presented. The scheme takes into account the possibility of the bifurcation mechanism of reaction development.

Посвящается памяти Р. Мессбауэра (31.01.1929–14.09.2011), лауреата Нобелевской премии, заложившего основы мессбауэрской (гамма-резонансной) спектроскопии

We have studied the cation distribution over the tetrahedral and octahedral sites in the spinel structure of nanocrystalline Ni x Zn1 − x Fe2O4 ferrites prepared by spray pyrolysis. 57Fe Mössbauer spectroscopy data for the ferrites demonstrate that, depending on the composition of the materials, the tetrahedral site may accommodate only Fe3+ (inverse spinel, x ≥ 0.4) or both Fe3+ and Zn2+ cations (mixed spinel, x = 0 and 0.2), which accounts for the fact that the composition dependence of the unit-cell parameter for the ferrites deviates from Vegard’s law.

This work is devoted to a detailed analysis of the interconnection between composition, cation distribution and acidic properties of the surface of nanocrystalline ferrites NixZn1−xFe2O4 obtained by aerosol pyrolysis. The detailed analysis of the Mössbauer spectra allows us to determine the distribution of cations between tetrahedral and octahedral positions in spinel structure. Depending on samples composition, the tetrahedral positions can be occupied by only Fe3+ cations (inverse spinel, x≥0.4) or by Fe3+ and Zn2+ cations (mixed spinel, x=0, 0.2). Increasing the nickel concentration in the ferrite leads to decrease in the number of strong acid centers on the surface. It was found that the decrease in the contribution of strong surface acid sites leads to an increase in sensory sensitivity of the ferrite towards ammonia. For ethanol detection an inverse relationship between sensor signal and surface acidity was observed.

Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The 57Fe Mössbauer spectrum of NiFe2O4 samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH3 has been studied using in situ conductance measurements. NiFe2O4 offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined.

Transmission electron microscopy, X-ray photoelectron spectroscopy, and 57 Fe Mössbauer spectroscopy have been used to study TiO 2 -based nanotubes (TNTs) intercalated with 57 Fe. A structural model of doped TNTs has been proposed that includes TNTs in the form of a “scroll” with nonmagnetic Fe-O-Fe layers spaced at ∼0.7-nm intervals in the interlayer spacing and ∼20-nm iron oxide clusters on the outer surface of the TNTs.