Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application.

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

Unusual effect of flow rate on retention in analytical supercritical fluid chromatography exemplified by polyethylene glycol separation.

We report a case of a peculiar effect of flow rate on retention in a separation of polyethylene glycol oligomers via supercritical fluid chromatography. During method development, we tested flow rate gradients and notices that for some PEG oligomers retention times at flow rate gradient were lower than at constant flow with the largest flow rate value used in a gradient. For instance, at BEH stationary phase and CO2-MeOH gradient from 10 to 35% at 20 min a PEG oligomer having mass of 1225 Da has a retention time 14 min at 1 mL/min flow rate, 10.3 at 2 mL/min and 9.5 min at 1-2 mL/min flow rate gradient. The effect is not unified for all PEG oligomers, it occurs only starting from a particular PEG molecular weight which depends on the stationary phase type and/or mobile phase conditions. We believe that such an unusual flow rate effects can happen in SFC on various occasions, not exclusively for flow rate gradients, and thus should be taken into account during method development or method transfer.

Adsorption of water and n-hexane on pristine and oxidized carbon nanotube supports of cobalt-based Fischer-Tropsch catalysts.

Adsorption of model polar (water) and non-polar (n-hexane) compounds on the surface of oxidized and non-oxidized carbon nanotube (CNT) supports at different stages of Co/CNT catalyst preparation has been studied to reveal the influence of the surface functionalization of the CNT support on the catalyst selectivity in Fischer-Tropsch synthesis (FTS). Dynamic vapor sorption experiments showed that defunctionalization of the surface of the CNT support during catalyst annealing and reduction led to its hydrophobization and, as a result, no noticeable difference was observed between the adsorption properties of the oxidized and non-oxidized supports towards water and hydrocarbons. Therefore, oxidation of the CNT support does not significantly affect the adsorption properties of the supported catalyst and it is not a crucial factor for the catalyst selectivity in FTS.

Kinetics of chlorate formation during ozonation of aqueous chloride solutions.

Chlorate ion ClO3- is formed as a result of the complex chemical interaction of ozone with chloride ion in aqueous solution. In neutral and basic solutions, chlorate is the main product. In acid solutions, the main product is molecular chlorine Cl2, and the yield of chlorate is 50-100 times lower. Dependencies have been studied of chlorate formation rate on significant experimental factors: concentrations of initial substances, ozone and chloride ion, acidity (pH), ionic strength and temperature of the reaction solution. The kinetic laws of chlorate generation have been established, and the expressions are given for rate constants of chlorate formation as functions of temperature and ionic strength. When tert-butanol is added to the reaction system, the formation of chlorate ceases, which is an evidence of the crucial role of free radical reactions in this process.

Kinetics of the defunctionalization of oxidized few-layer graphene nanoflakes.

Thermal defunctionalization of oxidized jellyfish-like few-layer graphene nanoflakes was studied under non-isothermal conditions by simultaneous thermal analysis. Activation energies for thermal decomposition of different oxygen functional groups were calculated by the Kissinger method and compared with those for oxidized carbon nanotubes. Oxygen content in graphene nanoflakes was found to significantly affect the decomposition activation energies of carboxylic and keto/hydroxy acids because of their acceptor properties and strong distortion of the graphene layers at the edges of the nanoflakes. The structure of the carbon material and the oxygen chemical state significantly influence the decomposition kinetics of thermally stable oxygen-containing groups. The activation energy for thermal decomposition of phenol groups (110-150 kJ mol-1) is close to that for graphene oxide reduction.

3D Frameworks with Variable Magnetic and Electrical Features from Sintered Cobalt-Modified Carbon Nanotubes.

3D frameworks of carbon nanotubes (CNTs) uniformly decorated by cobalt oxide or carbon-encapsulated cobalt nanoparticles were obtained by spark plasma sintering for the first time. The influence of the sintering temperature ( TS) and Co content on the morphology, structure, and electrical and magnetic properties of the obtained materials was investigated by Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and in situ magnetometry. It was shown that application of the SPS technique allowed simultaneous compaction of the material, formation of CNT framework, and Co oxide reduction. The appearance of the carbon shell around 4-10 nm Co particles was observed at TS > 600 °C. At higher TS, the Co particle size increased (up to 300 nm at 1400 °C), whereas the carbon shell ordered and thickened. The formation of large-size few-layers graphene sheets was observed at TS = 1400 °C. Electrical conductivity of the composites was found to be higher than that of sintered pristine CNTs and varied in the range of 500-12 500 Sm/m. Magnetic experiments demonstrated soft magnetization of the samples and the coercivity of 200-300 Oe. Thus, the obtained CNT-based material is simultaneously compact, formable, electroconductive, and ferromagnetic. Its properties can be tuned by variation of the sintering parameters. Synthesized cobalt-modified carbon 3D structures are promising for the application in magnetic separation, catalysis, fuel cells, and electromagnetic shielding.

Dissociation Constants of Perchloric and Sulfuric Acids in Aqueous Solution.

The experimental dissociation constants of strong acids are notoriously ill-defined, and it is necessary to rely on theoretical methods for their evaluation. We present a methodology for the theoretical evaluation of the dissociation constants, and the values of Ka for perchloric and sulfuric acids have been estimated. It has been shown that the acid dissociation constant Ka can be expressed as a product of two terms, Ka = Ka' × fHA∞, where Ka' is the apparent dissociation constant and fHA∞ is the infinite dilution activity coefficient of undissociated molecule of acid in liquid solution. The values of Ka' can be computed from readily available reference data. The limiting activity coefficients fHA∞ for strong acids can be determined by theoretical methods only. The following estimate for the limiting activity coefficients of perchloric and sulfuric acids has been obtained, -2.5 < log10 fHA∞ < -1.3. The ranges of values of the dissociation constants of HClO4 and H2SO4 at 25 °C have been determined; log10 Ka(HClO4) = 10.8-12.3; log10 Ka1(H2SO4) = 4.5-8.6.

Oxidation, defunctionalization and catalyst life cycle of carbon nanotubes: a Raman spectroscopy view.

Pristine, oxidized and defunctionalized carbon nanotubes (CNTs) were studied by Raman spectroscopy, X-ray diffraction, transmission electron microscopy and low temperature nitrogen adsorption. The Raman spectra of the studied samples in the range of 900-1800 cm-1 were deconvoluted into five components to reveal the CNT oxidation mechanism. It was found that the oxidation resulted in the reduction of graphite components and ordering of both the structured and defect part of CNTs. Acid treatment also led to different types of disorders in the surface layers of CNTs. Polyene-type, polyphenylene-type and turbostratic fragments were detected as a result of partial exfoliation. Investigation of defunctionalized CNTs showed the ordering of edge carbon atoms as well as the invariability of the total amount of defects. The study of CNTs as supports for Co-based catalysts revealed a simultaneous decrease in the number of defect fragments and increase in the number of edge carbon atoms during catalyst preparation and reduction.

Effect of anisotropy and drying of costal cartilage on its optical transmittance in laser reshaping of implants with 1, 2, and 3 mm in thickness.

BACKGROUND AND OBJECTIVE: Laser reshaping of cartilage is a prospective technique which can be applied for manufacturing the natural implants for otolaryngology and reconstructive surgery. Optical properties and optimal laser settings for laser reshaping of costal cartilage depend on its thickness, water content, and structural anisotropy of the tissue, in particular, the distinct orientation of collagen packing. The aim of the work is to study the effect of different collagen orientation, thickness, and drying of costal cartilage on its interaction with laser radiation. MATERIALS AND METHODS: Costal cartilage was cut along and crosswise the distinct collagen orientation. The dried and normal cartilage was used for the comparative analysis. The collagen package was studied using atomic force microscopy. The dried tissue was analyzed with thermogravimetry-differential scanning calorimetry (TG-DSC) analysis to reveal the residual water content. The optical transmittance was measured for two wavelengths λ: 1,560 and 532 nm. The reshaping of cartilage of 1-3 mm in thickness was performed with infrared laser with λ = 1560 nm while, the radiation with λ = 532 nm was used to determine the location of the IR beam. RESULTS: The transmittance of 532 nm radiation does not depend on collagen orientation and tissue drying. The IR radiation transmits better along the distinct collagen direction in dried cartilage while in normal cartilage the intensity of transmitted IR radiation increases intermittently passing crosswise and does not change dramatically with time along the collagen orientation. CONCLUSIONS: The effect of structural anisotropy of costal cartilage reveals itself in the increasing scattering of IR radiation with λ = 1,560 nm passing crosswise the collagen orientation when tissue water content is decreased. The radiation with λ = 1,560 nm is effective to perform the reshaping for cartilage of 1-3 mm in thickness; however, for 3 mm, the residual mechanical stress should be taken into account. Lasers Surg. Med. 48:887-892, 2016. © 2016 Wiley Periodicals, Inc.

IR laser and heat-induced changes in annulus fibrosus collagen structure.

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.