СОСТАВ И СТРОЕНИЕ СОЕДИНЕНИЙ СЕМЕЙСТВА ХАНТИТА

The literature data on the composition and structure of rare-earth borate compounds of the huntite family with the general composition LnM3(BO3)4, where Ln3+ = Y, La = Lu and M3+ = Al, Fe, Cr, Ga, Sc as well as a number of solid solutions with М3+ = Sc are systematized. The difference between the real compositions of crystals and the compositions of the initial mixture, the most characteristic of rare-earth scandium borates, is shown. The significant role of the composition in the manifestation of the compounds symmetry is established. The necessity of determining the crystals symmetry only on single-crystals with detailed analysis of diffraction reflections is proved. Morphotropic series were selected depending on changes in the ionic radii of Ln and M. Attention is paid to the peculiarity of the structural behavior of Cr3+ ions. It was revealed that the formation of solid solutions and internal solid solutions is most likely for rare-earth scandium borates. The implementation of polytypic modifications for LnM3(BO3)4, where M3+ = Al, Cr, and polymorphs for a number of Ln ions with M3+ = Fe, the existence of which is not excluded for M3+ = Sc, is demonstrated. Crystal-chemical effects observed for huntite-like crystals (morphotropy, isomorphism, polymorphism, polytypy; internal solid solutions; phase order-disorder phase transitions of different nature) with specific features of scandium borates are presented. The realization of polymorphism and polytypism for compounds of the huntite family confirms the crystal-chemical situation, according to which hightemperature polymorphic modifications should form more symmetrical compounds, but it is not typical of polytypic modifications.Проведена систематизация литературных данных по составу и строению редкоземельных боратов семейства хантита общего состава LnM3(BO3)4, где Ln3+ = Y, La-Lu, и M3+ = Al, Fe, Cr, Ga, Sc, а также ряда твердых растворов с М3+ = Sc. Показано отличие реальных составов кристаллов от составов исходной шихты, наиболее характерное для редкоземельных скандиевых боратов. Установлена значимая роль состава в проявлении симметрии соединений и доказана необходимость определения симметрии кристаллов только на монокристаллических объектах c детальным анализом дифракционных отражений. Выделены морфотропные ряды в зависимости от изменения ионных радиусов Ln и М. Обращено внимание на особенность структурного поведения ионов Cr3+. Выявлено, что образование твердых растворов и внутренних твердых растворов наиболее вероятно для редкоземельных скандиевых боратов. Продемонстрирована реализация политипных модификаций для LnM3(BO3)4, где M3+ = Al, Cr, полиморфов для ряда Ln c М3+ = Fe, существование которых не исключено для М3+ = Sc. Представлены кристаллохимические эффекты, наблюдаемые для хантитоподобных кристаллов (морфотропия, изоморфизм, полиморфизм, политипия; внутренние твердые растворы; фазовые переходы «порядок-беспорядок» разной природы) со спецификой для скандиевых боратов. Реализация полиморфизма и политипизма для соединений семейства хантита подтверждает кристаллохимическое положение, согласно которому высокотемпературные полиморфные модификации должны образовывать более симметричные соединения, а для политипных модификаций это не характерно

The role of composition and structure of vanadium-doped nanosized titanium(iv) oxides (anatase and η-phase) in the realization of photocatalytic, adsorption and bactericidal properties

Samples containing vanadium-doped nanosized titanium(iv) oxides with anatase and η-phase structures were prepared by a modified sulfate process, and samples with vanadium-doped η-phase were prepared for the first time. The bulk and the surface of the samples were characterized by a lot of methods, including X-ray diffraction, diffuse reflectance spectroscopy, X-ray absorption spectroscopy (EXAFS/XANES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The photocatalytic activity (PCA) of the samples was studied in the reaction of photodegradation of the cationic dye rhodamine 6G (in the visible region) and the systemic triazole fungicide difenoconazole (in the UV and visible regions). The PCA was found to be influenced by the phase composition of the samples, the composition of their surface, and nanosized titanium(iv) oxide modifications. Vanadium-doped samples with η-phase containing different ions (Ti3+, Ti4+, V4+, and V5+) and reactive OH groups on the nanoparticle surface exhibited the highest PCA. The samples were shown to have a higher adsorption capacity (AC) for the extraction of As(v) (the highest AC in the presence of vanadium-doped anatase and η-phase) and P(v) (the highest AC in the presence of undoped anatase and η-phase) anions from aqueous systems. The adsorption capacity correlates with the amount of reactive OH groups on the nanoparticle surface and does not depend on the modification of the adsorbent. Only vanadium-doped anatase containing the largest fraction of an amorphous component and the largest amount of SO4 2- groups on its nanoparticle surface exhibits antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Bacillus anthracoides. Vanadium doped anatase and η-phase can be used to purify aquatic environments of harmful organic pollutants and a wide range of anions. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique

COMPOSITION AND STRUCTURE OF THE HUNTITE-FAMILY COMPOUNDS

The literature data on the composition and structure of rare-earth borate compounds of the huntite family with the general composition LnM3(BO3)4, where Ln3+ = Y, La = Lu and M3+ = Al, Fe, Cr, Ga, Sc as well as a number of solid solutions with М3+ = Sc are systematized. The difference between the real compositions of crystals and the compositions of the initial mixture, the most characteristic of rare-earth scandium borates, is shown. The significant role of the composition in the manifestation of the compounds symmetry is established. The necessity of determining the crystals symmetry only on single-crystals with detailed analysis of diffraction reflections is proved. Morphotropic series were selected depending on changes in the ionic radii of Ln and M. Attention is paid to the peculiarity of the structural behavior of Cr3+ ions. It was revealed that the formation of solid solutions and internal solid solutions is most likely for rare-earth scandium borates. The implementation of polytypic modifications for LnM3(BO3)4, where M3+ = Al, Cr, and polymorphs for a number of Ln ions with M3+ = Fe, the existence of which is not excluded for M3+ = Sc, is demonstrated. Crystal-chemical effects observed for huntite-like crystals (morphotropy, isomorphism, polymorphism, polytypy; internal solid solutions; phase order-disorder phase transitions of different nature) with specific features of scandium borates are presented. The realization of polymorphism and polytypism for compounds of the huntite family confirms the crystal-chemical situation, according to which hightemperature polymorphic modifications should form more symmetrical compounds, but it is not typical of polytypic modifications

Single crystals of monticellite, activated with chromium and erbium ions, CaMgSiO_4:Cr:Er as an active medium for solid-state lasers

Translated from Russian (Report of the Institute of General Physics, Russian Academy of Sciences, Moscow (SU) 1997)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.190(VR-Trans--8394)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The role of composition and structure of vanadium-doped nanosized titanium(iv) oxides (anatase and η-phase) in the realization of photocatalytic, adsorption and bactericidal properties

Samples containing vanadium-doped nanosized titanium(iv) oxides with anatase and η-phase structures were prepared by a modified sulfate process, and samples with vanadium-doped η-phase were prepared for the first time. The bulk and the surface of the samples were characterized by a lot of methods, including X-ray diffraction, diffuse reflectance spectroscopy, X-ray absorption spectroscopy (EXAFS/XANES), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The photocatalytic activity (PCA) of the samples was studied in the reaction of photodegradation of the cationic dye rhodamine 6G (in the visible region) and the systemic triazole fungicide difenoconazole (in the UV and visible regions). The PCA was found to be influenced by the phase composition of the samples, the composition of their surface, and nanosized titanium(iv) oxide modifications. Vanadium-doped samples with η-phase containing different ions (Ti3+, Ti4+, V4+, and V5+) and reactive OH groups on the nanoparticle surface exhibited the highest PCA. The samples were shown to have a higher adsorption capacity (AC) for the extraction of As(v) (the highest AC in the presence of vanadium-doped anatase and η-phase) and P(v) (the highest AC in the presence of undoped anatase and η-phase) anions from aqueous systems. The adsorption capacity correlates with the amount of reactive OH groups on the nanoparticle surface and does not depend on the modification of the adsorbent. Only vanadium-doped anatase containing the largest fraction of an amorphous component and the largest amount of SO4 2- groups on its nanoparticle surface exhibits antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Bacillus anthracoides. Vanadium doped anatase and η-phase can be used to purify aquatic environments of harmful organic pollutants and a wide range of anions. © 2018 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique

The role of the compositions of HZSM-5 zeolites modified with nanosized anatase in propane and ethanol conversion

For the first time catalytic systems based on HZSM-5 zeolites (Si/Al=12, 25, 40) with nanosized anatase (NA) were obtained in situ by a modified hydrothermal method and a sol-gel method. Initial HZSM-5 and NA/HZSM-5 were characterized (XRPD, XAS, FT-IR, DSC, BET, XPS, SEM, TPD) and analyzed in the reactions of propane (liquefied petroleum gas) conversion (РС; temperature range 200–870 °С) with the formation of the main products propylene (C3H6, PP) and ethylene (C2H4, ETH) and liquid ethanol conversion (EC; temperature range 150–360 °C) with the formation of diethyl ether ((C2H5)2O, DEE) and ETH. In the PC reaction the maximum selectivity (SETH = 75%) and conversion (αP = 65%) were obtained on HZSM-5(40) (650 °С). With an increase in the NA content in NA/HZSM-5 SETH value increases up to 85%. In the EC reaction SDEE/ETH~98–99% was reached on HZSM-5(25) (200 °C) and HZSM-5(40) (300 °C); the αE to ETH is comparable (94%) for all HZSM-5 (300 °C). Modification of HZSM-5 with NA leads to a shift in the EC reaction temperature to lower temperature region (αE to ETH ~98% at 280 °C) with SDEE/ETH~94–100% for NA/HZSM-5(25) and NA/HZSM-5(12) obtained by a modified hydrothermal method. It was established the relationship between HZSM-5 and NA/HZSM-5 catalytic activity and their characteristics: Si/Al, NA content and Ti coordination number (NA/HZSM-5), the content of “zeolite water” with OH groups, specific surface area, meso- and micropores volume and spherical particles size (HZSM-5), surface energy of adsorption centers (HZSM-5 and NA/HZSM-5), and hence the content of acid sites, the strength of which is also determined by the temperature of the catalytic reaction. The reaction mechanisms have been presented. The obtained NA/HZSM-5 catalysts have a higher or comparable catalytic activity to commercial ones, but low cost, ease of preparation, and versatility. © 2021 Elsevier B.V

Impact of composition and structural parameters on the catalytic activity of MFI type titanosilicalites

Titanosilicalite of the MFI type was obtained via a hydrothermal method. Its initial and annealed at 75 °C (TS-1P(75)) and 500 °C (TS-1P(500)) forms were studied by X-ray powder diffraction (PXRD), X-ray absorption spectroscopy (XAS-method), Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), temperature-programmed ammonia desorption (TPD NH3), and pyridine adsorption (Py). The full-profile Rietveld method allowed us to observe the presence of the organic template tetrapropylammonium hydroxide (TPAOH) in the framework voids, as well as to determine the silicate module (Si/Ti = 73.5) and the distribution of Ti4+ ions over the MFI-type structure sites (Ti atoms replace Si ones in two positions: T1 and T6). The coordination numbers of titanium (CNTi = 4.6 for TS-1P and TS-1P(75), CNTi = 3.8 for TS-1P(500)) were established by the XAS-method. The catalytic activity of titanosilicalites was found in the reactions of nitrous oxide decomposition (the maximal decomposition rate is demonstrated for the TS-1P(75) sample), allyl chloride epoxidation to epichlorohydrin (the best combination of all indicators was exhibited for the TS-1P sample) and propane conversion (maximum propane conversion, and butadiene and propylene selectivity were observed in both TS-1P(75) and TS-1P(500) samples). Mechanisms for the catalytic processes are proposed. The relationship between the catalytic properties and the composition (Si/Ti), Ti4+ ion distribution over the MFI-type structure sites, the local environment of titanium ions, and the number of acid sites in the titanosilicalites are discussed. © 2022 The Royal Society of Chemistry