Increase In Platinum Content Research Articles

Chemoresistive gas-sensitive ZnO/Pt nanocomposites films applied by microplotter printing with increased sensitivity to benzene and hydrogen

ZnO/xPt nanopowders (x = 0, 0.5, 1, 3 mol%) were synthesised using the solvothermal method. The nanocomposites produced were characterised using a set of physiochemical analysis methods (XRD, BET, SEM, TEM and AFM). Synthesised ZnO/Pt powders were used to prepare special ink used for microplotter printing of gas-sensing receptor layers. The chemoresistive gas-sensing properties of CO, NH3, H2, C6H6, and NO2 were studied in depth in relation to the production of ZnO/xPt films. It was shown that, with an increase in platinum content, there was a significant decrease in the response to NO2 and CO, as well as an increase in the response to benzene and hydrogen. The mechanism of gas detection, including electronic and chemical sensing, was considered, kinetic properties were determined and response dependences on the content of hydrogen and benzene were established. Principal Component Analysis (PCA) was used to evaluate the correlation between the response of four used receptor nanomaterials and selectivity.

The effect of organic matter humification (aromaticity and oxidation degree) on structural and nanomorphological characteristics of humic nanocomposites of metallic platinum

BackgroundIt has been previously found that humic substances (HSs) can serve as the environmentally benign non-toxic agent for the preparation of magnetic and noble metals nanoparticles that are increasingly used in biomedicine. The structure of HSs and, hence, their synthetic potential depend on the source of their origin. Thus, humification character, determined by conditions and duration of complex transformation of organic remains in HSs can evidence their structure, in particular their aromaticity and oxidation degree. The incorporation of platinum nanoparticles in a shell of HSs allows obtaining aggregate-stable nanomaterials with directly controlled structural and nanomorphological characteristics, which combine the properties of platinum nanoparticles (selective cytotoxicity, anti-inflammatory activity, etc. And a complex of biological properties of HSs (antioxidant, immunomodulatory and anti-inflammatory activity. At the same time, the expression of valuable properties of platinum nanoparticles can be varied directly by changing their nanomorphological characteristics that strongly depend on the conditions of synthesis, in particular on the HSs type which is used for the synthesis. AimTo study the effect of humification (aromaticity and oxidation degree) of three types of humic substances extracted from natural Mongolia sources (therapeutic muds of Gurvan Nuur Lake, brown coal of Baganuur coal deposit and shale of Shine Hudag deposit) on structural and nanomorphological characteristics of Pt0-containing nanocomposites produced on their basis. MethodsNanocomposites with Pt0 content 1.2–6.5% were synthesized by reduction of hydrogen hexachloroplatinate with HSs in an aqueous-alkaline medium upon heating (90 °C). The yield of nanocomposites varied depending on type of HSs in the range 75–96%. The structure, composition and morphology of obtained nanocomposites were characterized by complex of modern physical and chemical methods (elemental analysis, XRD, SEM, TEM, IR- and optical-spectroscopy, DLS). ResultsThe platinum-containing nanocomposites have been synthesized using the reduction and stabilizing potentials of HSs with different degrees of humification (aromaticity and oxidation degree) and isolated from three natural Mongolian sources. The effect of functional composition, including oxidation and aromaticity degrees of HSs on the yield, quantitative and nanomorphological characteristics of produced platinum nanocomposites has been found. It is established that under the same reaction conditions platinum nanoparticles with face-centered cubic lattice and the smallest average size (9–15 nm) are formed from humic substances extracted from coal, while HSs derived from mud and shale afford the nanoparticles of larger size (18–28 and 16–26 nm respectively). The increase of platinum content in nanocomposites enlarges their average size, decreases their aggregate stability, as well as augments oxidation degree of HSs macromolecules. The reduction of platinum from precursor to the zero-valent state occurs due to oxidation of the phenolic and alcoholic hydroxyl groups, which are major components of HSs, as well as carbonyl groups. At the same time, HSs cover individual platinum nanoparticles, making them water soluble and preventing their aggregation. ConclusionThus, we have synthesized a series Pt0-containing nanocomposites containing 1.2–6.5% with use as reducing and stabilizing matrix of natural available HSs with different humification characteristics (aromaticity and oxidation degree) and isolated from three natural Mongolia sources It is found that obtained nanocomposites are formed in form of platinum nanoparticles mainly of spherical shape and size of 3–42 nm distributed in a matrix of HSs. Polyfunctional composition of HSs is determined by conditions of their transformation and degree of humification, which provides their reducing and stabilizing properties during the synthesis of platinum metallic nanocomposites. It is established that Pt0 nanoparticles with the smallest average size and the highest aggregate stability are generated from HSs-coal with the lowest oxidation degree. These data contribute significantly to understanding of possible control of the nanomaterials synthesis and prediction of their properties.

A Magnetic and Magneto-Optical Investigation of Co-Pt Alloy Nanowire Arrays

We have investigated the magneto-optical properties of highly ordered Co-Pt alloy nanowire arrays embedded in anodic aluminum oxide templates. The magnetic field-dependent Stokes parameters, Faraday rotation angle and ellipticity were investigated by an in-house magneto-optical measurement system. The extracted hysteresis loops are broadly consistent with magnetic hysteresis loops obtained from the vibrating sample magnetometer. The maximum Faraday rotation angle and ellipticity of these samples were examined as a function of nanowire composition. With an increase of platinum content from 9 at.% to 86 at.% in the as-deposited nanowire arrays, the maximum Faraday rotation angle per length decreases linearly from 1.39 x 10(3) degrees/cm to 1.58 x 10(2) degrees/cm. The maximum ellipticity shows a similar behavior with the composition. These linear relationships suggest a dilution model for the magnetic moment in the alloy nanowires. Our results indicate that magneto-optical measurements comprise an effective and sensitive method for monitoring the behavior of AAO-based magnetic nanowire arrays.

Efficient production of hydrogen by photo-induced reforming of glycerol at ambient conditions

Photocatalytic reforming of aqueous solutions of glycerol at ambient conditions has been investigated with the use of Pt/TiO 2 photocatalysts and a solar light-simulating source. The effects of platinum loading, photocatalyst content in suspension, glycerol concentration, solution pH and temperature on the reaction rate have been studied in detail. Results obtained show that the reaction proceeds with intermediate production of methanol and acetic acid and eventually results in complete conversion of glycerol to H 2 and CO 2. Optimal results are obtained for TiO 2 photocatalyst loaded with 0.1–0.5 wt.% Pt, whereas further increase of platinum content has a detrimental effect on photocatalytic performance. The reaction is favored over neutral and basic solutions, compared to acidic solutions, and the reaction rate increases substantially with increasing temperature from 40 to 60–80 °C. For high glycerol concentrations (∼1 mol L −1) the rate of hydrogen evolution is about two orders of magnitude higher, compared to that obtained for pure water, rendering the process suitable for application. It is concluded that glycerol photoreforming at ambient conditions may provide an efficient and low cost method for the production of renewable hydrogen.

Hydroisomerization of Ethylbenzene on Mordenite-Based Bifunctional Catalysts with Different Platinum Contents

A commercial Na-mordenite sample underwent ion exchange with HCl. The ion-exchanged sample was sequentially submitted to hydrothermal treatments at 823, 873 and 923 K, each followed by acid leaching of the extraframework alumina (EFAL) generated. Six mordenite samples, presenting different framework and extraframework compositions, were obtained. These samples were used to prepare bifunctional catalysts by mixing them with Pt/Al2O3 in different proportions. The generated samples presented distinct platinum contents and were tested in the hydroisomerization reaction of ethylbenzene. A maximum xylene selectivity at about 0.45 wt% of platinum was observed. Normally, the total activity increased as the platinum content increased; this effect was more pronounced in the samples which presented lower mesoporosity. The most dealuminated sample, which presented a high mesoporosity, did not show any change in activity with the increase in platinum content.

Involvement of protein kinase C in phorbol ester-induced sensitization of HeLa cells to cis-diamminedichloroplatinum(II).

We have investigated the effect of tumor promoting phorbol esters on the antiproliferative actions of several antitumor agents. Pretreatment of HeLa cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) or phorbol 12,13-dibutyrate (PDBu) caused a significant (9-fold) increase in cellular sensitivity to cis-diamminedichloroplatinum(II) (CP). TPA also sensitized HeLa cells to melphalan (2.5-fold) but had no effect on the antiproliferative activity of bleomycin, doxorubicin, vincristine, or mitomycin C. The sensitization of HeLa cells by TPA was concentration-dependent up to 1 nM and paralleled the activation of protein kinase C by TPA measured in vitro. The maximum stimulation of protein kinase C (6-fold) was observed with 10 nM TPA. 4 alpha-Phorbol 12,13-didecanoate neither activated protein kinase C nor sensitized HeLa cells to CP. 4-O-Methyl-TPA, which does not affect cell cycle distribution of HeLa cells, also sensitized these cells to CP by 6-fold and activated protein kinase C by 3-fold. Inhibitors of protein kinase C, such as palmitoylcarnitine and sphingosine, antagonized PDBu-induced sensitization of HeLa cells to CP. The maximum sensitization of HeLa cells to CP required prolonged pretreatment (greater than or equal to 24 h) with phorbol esters but could not be explained by down-regulation of protein kinase C. For example, 4-O-methyl-TPA caused no down-regulation of protein kinase C. Moreover, TPA caused substantial down-regulation of protein kinase C (1% of control) in A-253 cells but failed to sensitize A-253 cells to CP. TPA (100 nM), however, activated protein kinase C in A-253 cells by 5.5-fold. Therefore, activation of protein kinase C by TPA appears to be necessary but not sufficient for cellular sensitization to CP. The sensitization of HeLa cells by TPA was associated with a concentration- and time-dependent increase in cellular platinum content. The protein synthesis inhibitor cycloheximide (10 micrograms/ml) blocked sensitization of HeLa cells to CP as well as the increase in platinum content caused by a 24-h pretreatment with PDBu.

Competition between heterogeneous and homogeneous orderings in Cn3Pt(23at.%Pt)

Abstract An investigation into the ordering process in a Cu[sbnd]23 at.% Pt alloy is carried out by differential thermal analysis and precise X-ray measurement. The two-stage ordering that has been observed in a Cu[sbnd]19 at.% Pt alloy is observed but the relative dominancy between the two stages is found to be considerably altered by a slight increase in platinum content. Through isothermal annealing the stage I (at lower temperature) regime is associated with the ordering by heterogeneous nucleation and growth, while the stage II (at higher temperature) regimes is associated with the homogeneous ordering. Since the activation energy deduced for each stage of ordering is comparable, in contrast to the result in the Cu[sbnd]19 at.% Pt alloy where the stage I ordering is by far predominant, competition between the two stages occurs on isothermal annealing in a certain range of temperatures. Because of the competition, a mixed microstructure with the characteristic antiphase domain morphologies correspondi...

Effect of platinum concentration and dispersion on the deactivation of Pt/Al2O3 catalysts in the dehydrogenation of higher normal paraffins

Pt/Al/sub 2/O/sub 3/ (PAC) catalysts with 0.3-0.6 mass % platinum are used in dehydrogenation of higher normal paraffins and in reforming. The patent literature indicates a broader range of platinum contents for these catalysts. On increasing the platinum content from 0.25 to 1.0 mass %, the activity of these catalysts in the dehydrogenation of higher normal paraffins increases, while the specific activity and selectivity relative to normal monoolefins are not altered for identical conversions. In this work the authors studied the effect of the platinum concentration and dispersion in PAC on deactivation in the dehydrogenation of higher normal paraffins and elucidated the behavior of these catalysts in a study of PAC with added lithium, indium and rhenium. It is concluded that in the dehydrogenation of normal paraffins, Pt/Al/sub 2/O/sub 3/ catalysts have greater stability with an increase in platinum content and increase in platinum dispersion with identical platinum concentration; and, the stability of these catalysts increases and their tendency towards carbon deposition decreases with increasing catalyst activity.