Mechanochemical, Sonochemical and Hydrothermal Activation of Niobium Pentoxide and its Catalytic Properties

Modification of niobium pentoxide with different dispersity via mechanochemical, ultrasound, hydrothermal and microwave treatments (MChT, UST, HTT, and MWT, respectively) has been studied. All types of treatment do not change of phase composition but leads to improvement (at HTT and MWT) or, on contrary, breaking of crystal structure (at MChT and UST) and variation of crystallite size and specific surface area. UV-Vis measurements display increase of absorption in visible region. As a result, modified samples show higher photocatalytic activity at degradation of rhodamine B under visible irradiation. Similarly, initial and modified Nb2O5 samples are catalysts for mechanochtmical and sonochemical destruction of the same dye. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3515

Effect of precursor and surfactant nature on geometrical characteristics of mesoporous silicas

Bimodal mesoporous silicas and materials MCM-41 type were synthesized with the use as a template cationic surfactants distinguished by a length of the alkyl chain. Fumed silica, tetraethyl orthosilicate as well as of mixture these compounds were applied as a silicate precursor. Obtained samples have been characterized by the powder X-ray diffraction technique and adsorption measurements. Specific surface area, pore diameter, pore size distribution was determined from nitrogen ad(de)sorption isotherms at 77 K for the silicas prepared. The products with bimodal pore distribution have not ordered structure and contain macropores and mesopores, whose sizes are typical for MCM-41 materials. Effect of surfactant and precursor nature on the geometrical features of the ordered structure of MCM-41 type and bimodal porous materials was studied

High-pressure cryogelation of nanosilica and surface properties of cryosilicas

Silica cryogels (cryosilicas) in a powder state were synthesized with different concentrations of fumed silica A-300 (CA-300 = 5-20 wt.%), sonicated in aqueous suspension, then frozen at -14 oC at different pressures in a high-pressure stainless steel reactor (a freezing bomb), and dried in air at room temperature. To analyze the effects of low temperature and high pressure, samples were also prepared at -14 oC or room temperature and standard pressure. The structural and adsorption properties of the powder materials were studied using nitrogen adsorption, high-resolution transmission electron microscopy, infrared spectroscopy, thermogravimetry, low-temperature 1H NMR spectroscopy and thermally stimulated depolarization current. The structural, textural, adsorption and relaxation characteristics of high-pressure cryogel hydrogels and related dried powders are strongly dependent on the silica content in aqueous suspensions frozen at 1, 450 or 1000 atmospheres and then dried. The largest changes are found with CA-300 = 20 wt.% which are analyzed with respect to the interfacial behavior of nonpolar, weakly polar and polar adsorbates using low temperature 1H NMR spectroscopy

Surface Properties of Carbonaceous Solids as Examined by H NMR Spectroscopy Using the Bulk Freezing Procedure

It has been established that the type of adsorption sites on the surface of different carbonaceous materials [graphite oxide, thermo-expanded graphite, graphitized and non-graphitized carbons, carbon black, carbonated silicas (Carbosils)] can be determined using a chemical shift in the 1 H NMR spectra of adsorbed test compounds possessing different donor–acceptor properties and polarizability. This is due to the existence of local magnetic anisotropy regions near the carbon surface. The 1 H NMR measurements on adsorbent/adsorbed water/inert solvent interfaces provide an effective procedure for the differentiation of NMR signals from molecules bound with various types of surface sites. Variations in the free energy of water in the adsorption layer of Carbosils having different carbon contents on the silica surface and their free surface energy have been determined from measurements of the temperature dependence of the NMR signal for non-freezing water in the cooling process. A low degree of carbonization for the initial silica surface leads to a drastic increase in the aqueous interlayer thickness structurized by the surface

Methylene Blue Sorption Equilibria on Hydroxylated Silica Surfaces as Well as on Carbon–Silica Adsorbents (Carbosils)

The adsorption properties of hydroxylated silica gel as well as carbon–silica adsorbents (Carbosils) containing 5 and 18 w/w% carbon, both treated hydrothermally (with hydrogen peroxide solution) (HTT samples) and untreated, towards Methylene Blue (MB) were compared. The equilibrium adsorption of MB solutions of 6.5–7.0 × 10 −4 mol/l concentration and its dependence on pH were studied. At this concentration, ca. 30% of the adsorbent surfaces investigated were covered with MB molecules under optimal adsorption conditions. The presence of carbon deposits on the silica surface did not lead to a decrease in the adsorption capacity of Carbosils relative to that of hydroxylated silica. However, such deposits increased the resistance of the adsorbent towards the action of alkalis. Oxidation of the carbon deposit in the HTT process caused a further increase in this resistance. Hence, the adsorption mechanism of MB at equilibrium in individual systems of the type investigated can differ significantly. On the one hand, this mechanism is associated with the differing behaviour of silica over a wide range of pH relative to treated and untreated Carbosils and on the other hand with the specific properties of MB

Effect of hydrothermal treatment on the structure of water layers in carbosils suspensions

Carbon/silica samples prepared using mesoporous silica gel (SG, Si-60) modified by methylene chloride pyrolysis and then hydrothermal treatment using H2O2 as a modifier were studied by nitrogen adsorption, quasi-isothermal thermogravimetry and 1H NMR method. On the base of this method the concentration of strong (Cws) and weak (Cww) bound water, maximum decrease of Gibbs free energy of strongly and weakly bound water (?Gs and ?Gw) as well as surface free energy of the adsorbent in the aqueous medium was determined. No distinct correlation was found between the characteristics of the water layers adsorbed on the carbosils surface and the carbon phase content. Hydrothermal treatment affects the interactions of adsorbent surface with the aqueous phase insignificantly

Effect of hydrothermal modification on the porous structure and thermal properties of carbon-silica adsorbents (carbosils)

Characterisation of porous structure and thermal properties of unmodified and hydrothermally modified (using H2O2, under high pressure conditions) carbon-silica adsorbents (carbosils) prepared by dichloromethane pyrolysis (under dynamic conditions) on the surface of narrow pore silica were discussed. The analysis was made based on the data of low-temperature nitrogen adsorption/desorption isotherms, transmission electron microscopy (TEM) and the results of differential thermal analysis. It was stated that both porous structure and thermal properties of tested samples are in correlation with the morphology and topography of the carbon deposit. This deposit forms globules and aggregates whose size and position on the inner and outer surface of silica depends on the time of its carbonisation. It was stated that hydrothermal treatment (HTT) of the carbosils changes both the porous structure and thermal properties of the tested samples. As a result of HTT of silica, decondensation and recondensation of orthosilic acid on large particles of silica takes place. Then a decrease in the specific surface area and increase in the radius of pores are observed. In the case of carbosils these changes are smaller and depend on the accessibility of the silica surface, which is connected with topography of carbon deposit

Severe Secondary Polycythemia in a Female-to-Male Transgender Patient While Using Lifelong Hormonal Therapy: A Patient's Perspective

After a registered drug is available on the market and used in everyday circumstances, hitherto unknown adverse drug reactions (ADRs) may occur. Furthermore, the patient can experience a previously unknown course of a known ADR. Voluntary reports by patients play an important role in gaining knowledge about ADRs in daily practice. The Netherlands Pharmacovigilance Centre Lareb received a report from a 55-year-old female-to-male transgender patient who experiences secondary polycythemia while using lifelong testosterone therapy. The onset age of the symptoms was 38 years. The symptoms appeared gradually and after approximately 1 year it was clear that the patient's hemoglobin and hematocrit had started to increase. A Naranjo assessment score of 6 was obtained, indicating a probable relationship between the patient's polycythemia and use of the suspect drug. Polycythemia is a known ADR in testosterone treatment, but little attention has been paid to the possible severity and complications of these symptoms as well as the impact on the patient's well-being