Кристаллохимия и магнитные свойства гексаферрита BaFe-=SUB=-12-=/SUB=-O-=SUB=-19-=/SUB=- при гетеровалентном замещении железа цирконием

Samples of BaFe12O19 M-type barium hexaferrite with partial iron substitution by zirconium ions (concentration up to 10 at.%) have been synthesized and investigated. Studies of crystal features, phase composition, and magnetic properties were carried out using X-ray diffraction, Mössbauer spectroscopy, and VSM respectively. The presence of limited heterovalent isomorphism by the 2Fe3+ → Zr4+ + Fe2+ mechanism was shown. The limit of heterovalent isomorphic substitution by zirconium ions in barium hexaferrite (x = 0.6) was established. It was noted that additional sextets in the Mössbauer spectra of barium hexaferrite can be formed during the localization of Zr4+ ions predominantly in the 12k and 4f2 positions due to the frustration of the magnetic structure. The correlation between the chemical composition (concentration of zirconium ions), impurity phase formation, the peculiarities of the distribution of substituents over oxygen coordination, and the magnetic properties was established.

Origin of the Pd-Rich Pentlandite in the Massive Sulfide Ores of the Talnakh Deposit, Norilsk Region, Russia

Pd-rich pentlandite (PdPn) along with ore-forming pentlandite (Pn) occurs in the cubanite and chalcopyrite massive sulfide ores in the EM-7 well of the Southern-2 ore body of the Talnakh deposit. PdPn forms groups of small grains and comprises marginal areas in large crystals of Pn. The palladium content in PdPn reaches up to 11.26 wt.%. EDS elemental mapping and a contour map of palladium concentrations indicate distinct variations in the palladium content within and between individual grains. Palladium distribution in the large grains is uneven and non-zoned. PdPn was formed as the result of a superimposed process, which is not associated with either the sulfide liquid crystallization or the subsolidus transformations of sulfides. Deming regression calculations demonstrated the isomorphic substitution character of Ni by 0.71 Pd and 0.30 Fe (apfu), leading to PdPn occurrence. The replacement of Ni by Fe may also indicate a change in sulfur fugacity, compared to that taking place during the crystallization of the primary Pn. The transformation of Pn into PdPn could have occurred under the influence of a Pd-bearing fluid, which separated from the crystallizing body of the massive sulfide ores.

Computational study on Strontium ion modified Fibronectin-Hydroxyapatite interaction

Protein adsorption is the first key step in cell-material interaction. The initial phase of such adsorption process can only be probed using modelling approaches like molecular dynamics (MD) simulation. Despite a large number of studies on the adsorption behaviour of proteins on different biomaterials including hydroxyapatite (HA); little attention has been paid towards quantitative assessment of the effects of various physicochemical influencers like surface modification, pH, and ionic strength. Among these factors, surface modification through isomorphic substitution of foreign ions inside the apatite structure is of particular interest in the context of protein-HA interaction as it is widely used to tailor the biological response of HA. Given this background, we present here the molecular-level understanding of fibronectin (FN) adsorption mechanism and kinetics on Sr2+-doped HA (001) surface, at 300K by means of all atom molecular dynamics simulation. Electrostatic interaction involved in adsorption of FN on HA was found to be significantly modified in presence of Sr2+ doping in apatite lattice. In harmony with the published experimental observations, the Sr-doped surface was found to better support FN adhesion compared to pure HA, with 10 mol% Sr-doped HA exhibiting best FN adsorption. Sr2+ ions also influence the stability of the secondary structure of FN, as observed from the root mean square deviation (RMSD) and root mean square fluctuation (RMSF) analysis. The presence of Sr2+ enhances the flexibility of specific residues (residue no. 20-44, 74-88) of the FN module. Rupture forces to disentangle FN from the biomaterials surface, obtained from steered molecular dynamics (SMD) simulations, were found to corroborate well with the results of equilibrium MD simulations. One particular observation is that, the availability of RGD motif for the interaction with cell surface receptor integrin is not significantly influenced by Sr2+ substitution. Summarizing, the present work establishes a quantitative foundation towards the molecular basis of the earlier experimentally validated better cytocompatibility of Sr-doped HA.

Comparative Acid Leaching Study of Mongolian Muscovite and Montmorillonite Clay Minerals

Acid activation is the most commonly used method to enhance the chemical and physical properties of clay minerals. Porous structure formation behavior depends on the crystal structure of clay minerals. Within the same structure of clay minerals, their resistance to acid also varies. Acid leaching has been used to increase the surface area of clay minerals and obtain solids with high porosity and many acidic sites. This paper is focused on the results of acid leaching of Mongolian clay minerals (montmorillonite and muscovite). Both clay minerals belong to a group of phyllosilicates with the 2:1 crystal structure. The influence of acid concentration and leaching time on the porous properties of silica was studied. Initially, the montmorillonite was pre-treated by a simple physical purification methods. The montmorillonite and muscovite were acid leached by a 10% hydrochloric acid solution in an autoclave at 120°C for 10h. X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and the surface area used for characterization of the raw and leached samples. The surface area of leached montmorillonite increased up to 77% and muscovite up to 63%. Clay mineral’s swelling character and isomorphic substitution of the octahedral layer show the main influence on porous structure formation.

Recent Advances in Catalysis Based on Transition Metals Supported on Zeolites

This article reviews the current state and development of thermal catalytic processes using transition metals (TM) supported on zeolites (TM/Z), as well as the contribution of theoretical studies to understand the details of the catalytic processes. Structural features inherent to zeolites, and their corresponding properties such as ion exchange capacity, stable and very regular microporosity, the ability to create additional mesoporosity, as well as the potential chemical modification of their properties by isomorphic substitution of tetrahedral atoms in the crystal framework, make them unique catalyst carriers. New methods that modify zeolites, including sequential ion exchange, multiple isomorphic substitution, and the creation of hierarchically porous structures both during synthesis and in subsequent stages of post-synthetic processing, continue to be discovered. TM/Z catalysts can be applied to new processes such as CO2 capture/conversion, methane activation/conversion, selective catalytic NOx reduction (SCR-deNOx), catalytic depolymerization, biomass conversion and H2 production/storage.

Cu(II) and Cd(II) Removal from Aqueous Solution with LDH@GO-NH2 and LDH@GO-SH: Kinetics and Probable Mechanism

Two novel adsorbents of thiol- and amino-functionalized GO grafted onto LDH (LDH@GO-NH2 and LDH@GO-SH) were synthesized and contrasted for adsorption properties for Cu(II) and Cd(II). Characterization experiments illustrated that thiol group (-SH) and amino group (-NH2) were existed onto LDH@GO-NH2 and LDH@GO-SH. Adsorption isotherm results showed that the adsorption processes were satisfactorily fitted by both Langmuir and Freundlich models. The maximum adsorption capacity of Cd(II) on LDH@GO-SH at 308 K was 102.77 mg/g, which was about triple that of LDH@GO-NH2. The enhancement in adsorption capacity was due to the cooperative effect of LDH and GO-SH. The kinetic experimental data for LDH@GO-NH2 and LDH@GO-SH were found to be in good agreement with pseudo-second-order model. The thermodynamic parameters calculated from the temperature dependent adsorption isotherms indicated that the adsorption was a spontaneous and endothermic process. The possible adsorption mechanisms comprising formation of precipitation, isomorphic substitution of Mg(II), and formation of complexation with amino-groups and thiol-groups were proposed. Desorption experiments put into evidence that the LDH@GO-NH2 and LDH@GO-SH may be promising suitable candidates for the remediation of metal ions from aqueous solutions in real work in the near future.

Maghemite in Brazilian Iron Ores: Quantification of the Magnetite-Maghemite Isomorphic Series by Χ-ray Diffraction and the Rietveld Method, and Confirmation by Independent Methods

Maghemite (γ-Fe2O3) is a mineral formed from magnetite oxidation at low temperatures, an intermediate metastable term of the magnetite to hematite oxidation and could be mixed with both. It has magnetic susceptibility similar to magnetite, crystal structure close to magnetite with which it forms a solid solution, while compositionally it equals hematite. Maghemite is thus easily misidentified as magnetite by Χ-ray diffraction and/or as hematite by spot chemical analysis in iron ore characterization routines. Nonstoichiometric magnetite could be quantified in samples of Brazilian soils and iron ores by the Rietveld method using a constrained refinement of the Χ-ray patterns. The results were confirmed by reflected light microscopy and Raman spectroscopy, thus qualitatively validating the method. Χ-ray diffraction with the refinement of the isomorphic substitution of Fe2+ by Fe3+ along the magnetite-maghemite solid solution could help to suitably characterize maghemite in iron ores, allowing for the evaluation of its ultimate influence on mineral processing, as its effect on surface and breakage properties.