Leonid A. Solovyov

Sonochemical coating of paper by microbiocidal silver nanoparticles.

Colloidal silver has gained wide acceptance as an antimicrobial agent, and various substrates coated with nanosilver such as fabrics, plastics, and metal have been shown to develop antimicrobial properties. Here, a simple method to develop coating of colloidal silver on paper using ultrasonic radiation is presented, and the coatings are characterized using X-ray diffraction (XRD), high resolution scanning electron microscope (HRSEM), and thermogravimetry (TGA) measurements. Depending on the variables such as precursor concentrations and ultrasonication time, uniform coatings ranging from 90 to 150 nm in thickness have been achieved. Focused ion beam (FIB) cross section imaging measurements revealed that silver nanoparticles penetrated the paper surface to a depth of more than 1 μm, resulting in highly stable coatings. The coated paper demonstrated antibacterial activity against E. coli and S. aureus, suggesting its potential application as a food packing material for longer shelf life.

Characterization of mesoporous carbons synthesized with SBA-16 silica template

The structure of ordered mesoporous carbons (OMC) synthesized with sucrose, furfuryl alcohol or acenaphthene using the SBA-16 mesoporous silica template with cubic Imm structure has been investigated with X-ray powder diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and N2 adsorption. This work shows that, in contrast to carbons prepared from sucrose by using SBA-15 silica as template, the impregnation of SBA-16 with sucrose failed to produce OMC with cubic Imm structure. However, when furfuryl alcohol and acenaphthene were used as carbon precursors, the cubic Imm structure was retained in the products. Thus, the latter carbon precursors were more suitable than sucrose for the formation of rigidly interconnected carbon bridges through narrow apertures of the cage-like siliceous SBA-16 mesostructure. In particular, the use of furfuryl alcohol as carbon precursor allowed us to control the degree of mesopore filling in SBA-16 and consequently, to synthesize hollow or fully filled cage-like silica–carbon mesostructures as was done in the case of channel-like SBA-15. In the case of acenaphthene only fully filled mesostructures were formed but with a much higher degree of graphitization. In the present work, we took advantage of the recent developments in the synthesis of SBA-16 with tailored diameter and entrance size of mesopores and made a step forward in the fabrication of OMC by using cage-like mesoporous silicas with narrow interconnections as templates.

Transformation of highly ordered large pore silica mesophases (Fm3m, Im3m and p6mm) in a ternary triblock copolymer-butanol-water system.

Exceptional control of the phase behavior of highly ordered large pore mesostructured silica (with the choice of Fm3m, Im3m or p6mm symmetry) is achieved using a triblock copolymer (EO(106)PO(70)EO(106)) and butanol at low acid concentrations.

X-ray structural modeling of silicate mesoporous mesophase material

Abstract Rietveld’s technique in combination with a continuous electron density representation was applied to structural modeling of highly ordered pure siliceous mesoporous mesophase material C16-SiO 2 -MMM of the MCM-41 type prepared by hydrothermal synthesis in the presence of C 16 H 33 N(CH 3 ) 3 Br. Several important characteristics of the material in both as-synthesized and calcined forms were revealed. In particular, it was found that mesopores in the materials are of true hexagonal shape, and the wall electron density seems to be not continuous.

Synthesis of ZnO and Zn nanoparticles in microwave plasma and their deposition on glass slides.

This work represents a new method to synthesis of ZnO and/or Zn nanoparticles by means of microwave plasma whose electrons are the reducing agents. Glass quadratic slides sized 2.5 x 2.5 cm were coated by ZnO and/or Zn particles whose sizes ranged from a few micrometers to approximately 20 nm. The size of the particles can be controlled by the type of the precursor and its concentration. In the current paper, the mechanism of the reactions of ZnO and/or Zn formation was proposed. Longer plasma irradiation and lower precursor concentration favor the fabrication of metallic Zn nanoparticles. The nature of the precursors ion (acetate, nitrate, or chloride) is also of importance in determining the composition of the product. The glass slides coated by ZnO and/or Zn nanoparticles were characterized by HR-SEM, HR-TEM, AFM, XRD, ESR, contact angle and diffuse reflectance spectroscopy (DRS).

Synthesis and characterization of large-pore ordered mesoporous carbons using gyroidal silica template

Replication of mesoporous silica to ordered mesoporous carbon (OMC) has been studied with the recently discovered large-pore MCM-48-like cubic Iad mesoporous silica (KIT-6), with particular interest in the effect of the silica pore connectivity. The carbonization was performed with sucrose or furfuryl alcohol under various conditions. The resultant OMC samples were characterized by powder X-ray diffraction, transmission electron microscopy, and nitrogen physisorption. The results indicate that the OMC pore structures and diameters can be systematically regulated by hydrothermal treatment of the silica template during synthesis, post-synthetic surface modification, variation of the silica source to surfactant ratio, and choice of catalysts for the polymerization of furfuryl alcohol. Thereby, the controllable range of OMC pore diameters has been increased to 13 nm from the 2–5 nm range obtained so far. Here, the most important factor is to control the pair-wise joining of enantiomeric carbon frameworks formed inside the silica template.

Formation of bimetallic Au-Pd and Au-Pt nanoparticles under hydrothermal conditions and microwave irradiation.

The reduction of chlorocomplexes of gold(III) from muriatic solutions by nanocrystal powders of palladium and platinum at 110 and 130 °C under hydrothermal conditions and the action of microwave irradiation has been investigated. The structure and composition of the solid phase have been characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and chemical methods. Bimetallic particles with a core-shell structure have been revealed. The obtained particles are established to have a core of the metal reductant covered with a substitutional solid (Au, Pd) solution in case of palladium, and isolated by a gold layer in the case of platinum. The main reason for such a difference is the ratio between the rates of aggregation and reduction. It has been shown by the example of the Au-Pd system that the use of microwave irradiation allows us not only to accelerate the synthesis of particles but also to obtain more homogeneous materials in comparison with conventional heating.

X-ray diffraction analysis of mesostructured materials by continuous density function technique

Abstract A continuous density function technique has been developed for X-ray diffraction (XRD) structural investigations of mesostructured materials. The technique is designed for the analysis of the density distribution in materials exhibiting nanoscale (2-50 nm) ordering of structural elements without atomic long-range order. The results of structure investigations of a series of silicate, metallosilicate and carbon mesostructured materials with hexagonal and cubic symmetry are presented.

Structure and sorption properties of a zeolite-templated carbon with the EMT structure type.

An ordered microporous carbon material was prepared by the nanocasting process using the EMC-2 zeolite (EMT structure type) as a hard template. X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed long-range ordering in the material that resulted from the negative replication of the host template. The carbon porous network replicating the zeolite structure was modeled by overlapped spherical voids with diameters determined from the XRD pattern that displayed up to six distinct peaks. The surface delimiting the 3D interconnected porosity of the solid has a complex morphology. The pore size distribution calculated from the XRD-derived structural model is characterized by a maximum at 1.04 nm related to the long-range-ordered microporous network. Complementary studies by immersion calorimetry revealed that most of the porosity was characterized by a size above 1.5 nm. These porous features were compared to data resulting from classical analysis (DR, DFT, BET, etc.) of the N2 (77 K) and CO2 (low and high pressure, 273 K) physisorption isotherms. The limitations of these approaches are discussed in light of the pore size distribution consistently determined by XRD and immersion calorimetry measurements.

Influence of the composition and structure of the glass-crystalline shell of cenospheres on helium permeability

We studied the interrelation between the composition, morphology, and helium permeability of the shell of narrow fractions of nonmagnetic nonperforated cenospheres extracted from cenosphere concentrates of fly ash of the sialic type with the use of technological stages of hydrodynamic, magnetic separation, sizing, and aerodynamic classification. For the interval of variation of Al2O3 content from 20 to 38 wt %, the regression equation [SiO2]/[Al2O3] = 5.06 − 0.1[Al2O3] is established, with the correlation coefficient equal to −0.98. It is found that, together with the growth in the concentration of Al2O3 in the indicated interval, the content of the originally mullite phase increases from 1.3 to 42.4 wt %, and this is accompanied by the growth of the helium permeability of the glass-crystalline shell of the cenospheres.