Vladimir Uvarov

Nanocrystalline tin disulfide coating of reduced graphene oxide produced by the peroxostannate deposition route for sodium ion battery anodes

A highly stable sodium ion battery anode was prepared by deposition of hydroperoxostannate on graphene oxide from hydrogen-peroxide-rich solution followed by sulfidization and 300 °C heat treatment. The material was characterized by electron microscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy which showed that the active material is mostly rhombohedral SnS2 whose (001) planes were preferentially oriented in parallel to the graphene oxide sheets. The material exhibited >610 mA h g−1 charge capacity at 50 mA g−1 (with >99.6% charging efficiency) between 0 and 2 V vs. Na/Na+ electrode, high cycling stability for over 150 cycles and very good rate performance, >320 mA h g−1 at 2000 mA g−1.

Development and metrological characterization of quantitative X-ray diffraction phase analysis for the mixtures of clopidogrel bisulphate polymorphs

Clopidogrel bisulphate (CLP) is a pharmaceutical compound with a novel mechanism of action for the reduction of atherosclerotic events. Only two crystalline forms (CLP I and CLP II) among the six known polymorphs of CLP have therapeutic activity. The structure of the CLP I polymorph is unknown and the structure of the CLP II polymorph is known only partially. Two techniques of X-ray diffraction quantitative phase analysis have been developed in this work for the quantification of CLP I and CLP II in their mixtures. The first technique is based on use of the whole powder pattern decomposition method (WPDM). WPDM was realized through Powder Cell for Windows v.2.4 (PCW) freeware. The second technique is based on the classical direct method. Metrological characterization and comparison of methods have been performed on the mixtures with known phase composition as well as on the real samples with varying phase content. Quantitative phase analyses of 120 specimens containing mixtures of forms I and II of CLP were performed using both developed techniques. Absolute and relative errors and reproducibility of both methods were found to be very similar. The statistical analysis of obtained results revealed that the WPDM gives higher accuracy. We found that the limit of quantification using both methods is 1.0-1.5wt.% of phase content in the mix.

X-ray diffraction and SEM study of kidney stones in Israel: quantitative analysis, crystallite size determination, and statistical characterization

Urinary calculi have been recognized as one of the most painful medical disorders. Tenable knowledge of the phase composition of the stones is very important to elucidate an underlying etiology of the stone disease. We report here the results of quantitative X-ray diffraction phase analysis performed on 278 kidney stones from the 275 patients treated at the Department of Urology of Hadassah Hebrew University Hospital (Jerusalem, Israel). Quantification of biominerals in multicomponent samples was performed using the normalized reference intensity ratio method. According to the observed phase compositions, all the tested stones were classified into five chemical groups: oxalates (43.2%), phosphates (7.7%), urates (10.3%), cystines (2.9%), and stones composed of a mixture of different minerals (35.9%). A detailed analysis of each allocated chemical group is presented along with the crystallite size calculations for all the observed crystalline phases. The obtained results have been compared with the published data originated from different geographical regions. Morphology and spatial distribution of the phases identified in the kidney stones were studied with scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). This type of detailed study of phase composition and structural characteristics of the kidney stones was performed in Israel for the first time.

Crystallization of carbamazepine pseudopolymorphs from nonionic microemulsions.

Crystallization of carbamazepine (CBZ), an antiepileptic drug, precipitated from confined spaces of nonionic microemulsions was investigated. The study was aimed to correlate the structure of the microemulsion [water-in-oil (W/O), bicontinuous, and oil-in-water (O/W)] with the crystalline structure and morphology of solid CBZ. The precipitated CBZ was studied by DSC, TGA, powder XRD, single-crystal XRD, SEM, and optical microscopy. The results suggest that the microstructure of the microemulsions influences the crystallization process and allows crystallizing polymorphs that exhibit different crystal structure and habits. W/O nanodroplets orient the crystallizing CBZ molecules to form a prismlike anhydrous polymorphic form with monoclinic unit cell and P21/n space group. Bicontinuous structures lead to platelike dihydrate crystals with orthorhombic unit cell and Cmca space group. The O/W nanodroplets cause the formation of needlelike dihydrate crystals with monoclinic unit cell and P21/c space group. The morphological features of solid CBZ remain predetermined by the basic symmetry and parameters of its unit cell. Precipitation of CBZ pseudopolymorphs from supersaturated microemulsion is discussed in terms of oriented attachment that provides perfect packing of numerous separately nucleated ordered nuclei of CBZ into microscale platelets and then into macroscopic crystals. Crystallization from microemulsion media enabling one to obtain the drug (CBZ) with predicted structure and morphology should be of great significance for pharmaceutical applications.

Crystallite size--is it a new predictor for renal stone burden?

OBJECTIVE To evaluate the importance of stone composition and crystallite size in the formation of ultimate stone burden. Crystallite is the smallest building block, which is unique in size and architecture for each type of stone component. Currently, the knowledge about the clinical importance of crystallite size is very limited. METHODS The results of quantitative X-ray diffraction phase analysis performed on 286 kidney stones extracted during endourological surgery or expelled spontaneously were retrospectively analyzed. Stone composition and crystallite size were determined and were compared to the burden occupying the pelvicalyceal system. RESULTS A total of 286 renal stones were analyzed. Stones were low burden and high burden in 242 and 44 of cases, respectively. We observed statistically significant association of phosphates and urates with high-burden stones in contrast to oxalates, which formed mainly low-burden stones. Crystallite sizes were available for 179 stones. Large-sized crystallites of calcium oxalate monohydrate and hydroxyl apatite formed low-burden stones, whereas small-sized crystallites formed staghorn stones. Struvite and urates had a uniform average size of crystallites. CONCLUSION Oxalate stones have statistically significant association with smaller stones, whereas high-burden calculi are significantly associated with urates and phosphates, especially the struvite type. The smaller the crystallite size is to start with, the larger will be the ultimate stone burden. This rule is followed by calcium oxalate monohydrate and Apatite minerals.

Microemulsion‐Facilitated Crystallization of Carbamazepine

The crystallization patterns of carbamazepine precipitated from a confined microemulsion reservoir were studied by DSC, TGA, Powder XRD, single crystal XRD, SEM, and optical microscopy. The results suggest that interfacial fast nucleation and slow growth from O/W microemulsion leads to a selective, large, and better‐ordered single crystals of dihydrate form with primitive monoclinic unit cell with parameters a=10.16 Å, b=28.70 Å, c=4.93 Å, β=103.33°, cell volume of 1400.7 Å3, and space group P21/c. The crystal structure, as well as the habit, are strongly influenced by the heat dissipation and prefered molecular orientation at the interface.

XPS characterization of sodium percarbonate granulated with sodium silicate

Granular sodium percarbonate has been characterized by X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The O1s binding energy for the solvating hydrogen peroxide molecules is 535.8 eV. Sodium percarbonate is stabilized by sodium silicate and polyphosphate.

Near ultra-violet to mid-visible band gap tuning of mixed cation RbxCs1−xPbX3 (X = Cl or Br) perovskite nanoparticles

One of the most attractive features of perovskite materials is their chemical flexibility. Due to innovative chemical compositions of perovskites, their optical and structural properties, and functionalities have become more advanced, enabling better solar performance in photovoltaics, as well as robustness and excellent properties in the nanoscale for optoelectronics. The quest for novel perovskite compositions in the nano-scale is significantly important. This paper reports on a mixed-cation system of RbxCs1-xPbX3 (where X = Cl or Br) nanoparticles. The absorption of the nanoparticles is tunable in the near ultra-violet and visible regions between ∼395-525 nm for RbxCs1-xPbX3 (x = 0 to x = 0.8 and X = Cl or Br). The photoluminescence quantum yields (PLQY) of the mixed Rb+/Cs+ nanoparticle systems are comparable to the PLQY of CsPbX3 nanoparticles. Interestingly an attempt to synthesize Cl- and Br-based nanoparticles with high Rb+ content was successful, although possessing low tolerance factors. We conclude that these mixed Rb+/Cs+ nanoparticles are more adjustable to structural distortions caused by cation substitutions than their bulk counterparts, which opens a way towards the development of more advanced mixed-ion perovskite compositions in the nano-scale.

Hybrid bismuth oxyhalides@gypsum as self-cleaning composites: novel aspects of a sustainable photocatalytic technology for solar environmental cleanup

Herein we report the fabrication of a novel heterojunctioned BiOClxBr1−x@gypsum composite and its application as a self-cleaning surface for the straightforward use in construction and building materials. The morphology, chemical composition and crystal structure of the hybrid material were characterized using X-ray diffraction and scanning electron microscopy. The photocatalytic activity of the new composite was investigated for the degradation of naphthalene and rhodamine B (RhB) under visible light (λ ≥ 420 nm) irradiation. Our results show rapid and complete destruction of the RhB dye after only 4 minutes under Xe visible light irradiation (422–740 nm) and 2.5 minutes under mild sunlight illumination. Total organic carbon measurements could verify the absolute mineralization of the recalcitrant naphthalene contamination, as a state of the art example, within 20 minutes of visible light illumination.

An estimation of the correctness of XRD results obtained from the analysis of materials with bimodal crystallite size distribution

36 powder artificial mixtures and 2 usual samples with a bimodal crystallite size distribution have been prepared and examined by an X-ray diffraction method. We estimated the capability of the Rietveld refinement at a “double-phase model” mode and the correctness of the results. The homogeneity and the crystallite sizes of pure phases used in the preparation of the mixtures were checked by TEM. In most cases, Rietveld refinement at a “double-phase model” mode provided reliable information about both the crystallite size and percentage of constituents. Reliability of XRD results was higher for the powder mixtures with a larger difference in crystallite sizes. It was found that the shape of the crystallites can have a significant impact on the analysis results, and for columnar crystals, the employed method did not always provide correct results. When size distribution of the material deviates from a bimodal one, the correctness of the result decreases. Such an investigation was performed for the first time.