Greater Catalytic Effect Research Articles

Preparation of CoFe@C composite modified electrode for neohesperidin dihydrochalcone sensing and its application in Chinese medicine.

CoFe@C was first prepared by calcining the precursor of CoFe-metal-organic framework-74 (CoFe-MOF-74), then an electrochemical sensor for the determination of neohesperidin dihydrochalcone (NHDC) was constructed, which was stemmed from the novel CoFe@C/Nafion composite film modified glassy carbon electrode (GCE). The CoFe@C/Nafion composite was verified by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) was used to evaluate its electrical properties as a modified material for anelectrochemical sensor. Compared with CoFe-MOF-74 precursor modified electrode, CoFe@C/Nafion electrode exhibited a great synergic catalytic effect and extremely increased the oxidation peak signal of NHDC. The effects of various experimental conditions on the oxidation of NHDC were investigated and the calibration plot was tested. The results bespoken that CoFe@C/Nafion GCE has good reproducibility and anti-interference under the optimal experimental conditions. In addition, the differential pulse current response of NHDC was linear with its concentration within the range0.08 ~ 20µmol/L, and the linear regressioncoefficient was 0.9957. The detection limit was as low as 14.2nmol/L (S/N = 3). In order to further verify the feasibility of the method, it was successfully used to determine the content of NHDC in Chinese medicine, with a satisfactory result, good in accordance with that of high performance liquid chromatography (HPLC).

Study on quantitative structure of coke deposition in UDH catalyst for acetylene hydrochlorination

ABSTRACT The catalyst made of Au, Cu and K according to a certain ratio which is defined as a UDH catalyst has a great catalytic effect on acetylene hydrochlorination. In order to clarify the formation mechanism of coke deposition in catalyst, the structure of coke deposition was quantified. Carbon deposits in the UDH catalyst are separated using Soxhlet extraction and rotary evaporation. Experimental techniques like gel chromatography, elemental analysis, H-NMR and FT-IR were applied for the characterization of coke deposition. The quantitative structure of the coke deposition was evaluated by the improved B-L method. The results show that the average molecular formula of the coke deposition is C40.82H33Cl15.55 which is a complex multiple-ring structure containing seven aromatic rings and five six-membered cycloalkane rings. The aromatic carbon fraction of the calculated coke deposition is 0.623, and the ratio of hydrogen to carbon atomic which are not replaced in aromatic ring moieties is 0.313. These results indicate that in the side reaction of acetylene hydrochlorination, substances with the ring structure are more likely to be generated, and the ring structure continues to increase, eventually forming coke deposition.

Tyrosinase-Based Biosensor-A New Tool for Chlorogenic Acid Detection in Nutraceutical Formulations.

The purpose of our research was to develop a new enzymatic biosensor, GPH-MnPc-Tyr/SPE, using as a support screen-printed carbon electrode (SPE) modified with graphene, manganese phthalocyanine, and tyrosinase, with the aim of developing sensitive detection of chlorogenic acid (CGA). To immobilise tyrosinase on the sensor surface, crosslinking with the glutaraldehyde technique was used, thus increasing the enzyme bioactivity on this electrode. The modified electrode has a great catalytic effect on the electrochemical redox of chlorogenic acid, compared to the simple, unmodified SPE. The peak current response of the biosensor for CGA was linear in the range of 0.1–10.48 μM, obtaining a calibration curve using cyclic voltammetry (CV) and square-wave voltammetry (SWV). Subsequently, the detection limit (LOD) and the quantification limit (LOQ) were determined, obtaining low values, i.e., LOD = 1.40 × 10−6 M; LOQ = 4.69 × 10−6 M by cyclic voltammetry and LOD = 2.32 × 10−7 M; LOQ = 7.74 × 10−7 M, by square-wave voltammetry (SWV). These results demonstrate that the method is suitable for the detection of CGA in nutraceutical formulations. Therefore, GPH-MnPc-Tyr/SPE was used for the quantitative determination of CGA in three products, by means of cyclic voltammetry. The Folin–Ciocalteu spectrophotometric assay was used for the validation of the results, obtaining a good correlation between the voltammetric method and the spectrophotometric one, at a confidence level of 95%. Moreover, by means of the DPPH method, the antioxidant activity of the compound was determined, thus demonstrating the antioxidant effect of CGA in all nutraceuticals studied.

An experimental investigation in the formation damage mechanism of deposited coke in in-situ combustion process using nuclear magnetic resonance

The success of an in situ combustion process is dependent on the stability and movement of the combustion front. During an in situ combustion process, coke is an important product for maintaining the stability of the combustion front. However, before being consumed by the combustion reaction, coke is deposited in the porous media; thus, it may cause the blockage of the pore throat and affect the subsequent air injection. In this study, the low-field nuclear magnetic resonance technique was applied to examine the influence of oxidized coke and pyrolyzed coke on the porous media. The results revealed that the coke deposition phenomenon was considerable in porous media and affected porosity. The formation damage was considerably severe in oxidized coke because of the drastic low-temperature oxidation. In case of the pyrolyzed core, the influence of coke on porosity is limited because of the low amount of coke generation. The average reduction in porosity was 21.90%, while that of the pyrolyzed coke is only 9.09%. Montmorillonite had the greatest catalytic effect on coke deposition for both oxidation and pyrolysis processes. Illite, kaolinite, and chlorite have an impact on coke deposition; however, because the change in porosity is attribute to a combination of multiple factors, the result is a lack of regularity. Heat causes the pore to reform and the fracture to form. The change in porous media can reduce the impact of coke deposition phenomenon on total porosity. Because of the high-temperature environment, this influence is more pronounced in the pyrolyzed core.

Effects of CO Atmosphere on the Pyrolysis of a Typical Lignite

AbstractTo reveal the effect mechanism of CO atmosphere on coal pyrolysis, a study on raw and demineralized lignite was carried out in a horizontal tube furnace under N2 and CO/N2 atmosphere. CO had a negligible effect on the char yield at low temperatures, whereas it enhances the char yield at temperatures higher than 550 °C. The release of tar was higher in the presence of CO above 450 °C because of more free radicals, which reduced low‐temperature crosslinking, and higher selectivity of hydroxyl groups to phenols in the CO‐containing atmosphere. The yields of CO2 and H2 increased, water and CO yields decreased under CO/N2 atmosphere. Light hydrocarbon gases were not affected by changing the reaction atmosphere. The difference between product yields from raw and demineralized coal confirmed that the catalysis of inherent minerals had a great catalytic effect on the water‐gas shift reaction and Boudouard reaction.

Ultrasound-assisted synthesis of 1,4-dihydropyridine derivatives by an efficient volcanic-based hybrid nanocomposite

A novel hybrid nanocomposite made of cellulose matrix and pumice volcanic rock as a nature basis is presented. This heterogeneous nanocomposite is has also been applied as a suitable biodegradable catalytic system for facilitating the organic reactions. In this work, firstly we try to perform well characterization on the prepared cellulose/pumice nanocomposite. Further, the catalytic activity of cellulose/pumice nanocomposite is investigated in the synthesis reactions of 1,4-dihydropyridine derivatives. Moreover, the role of ultrasound wave irradiation (using an ultrasound bath with 60 KHz and 150 W L−1) in catalyzing the synthetic reactions is precisely monitored. In summary, great synergistic catalytic effect between cellulose/pumice nanocomposite and ultrasound waves has led to obtain high reaction yields (97%) in short reaction times (10 min), under mild conditions.

Enhanced hydrogen storage properties of MgH2 by the synergetic catalysis of Zr0.4Ti0.6Co nanosheets and carbon nanotubes

Transition metal nanoparticles have shown great catalytic effect on MgH2, yet excellent cyclic stability can be attached due to the addition of carbon nanotubes. In this paper, MgH2 + 10 wt% Zr0.4Ti0.6Co /5 wt% Carbon nanotubes (CNTs) composite is designed to investigate the synergistic modification of Zr0.4Ti0.6Co nanosheets and carbon nanotubes on the hydrogen storage performance of MgH2. Compared with pure MgH2, the initial hydrogen release temperature of MgH2 + 10 wt% Zr0.4Ti0.6Co /5 wt% CNTs composite decreases to 180 °C and the composite can quickly release 90% H2 within 10 min at 300 °C. In addition, the completely dehydrogenated sample can absorb 3.51 wt% H2 within 20 min under 3 Mpa hydrogen pressure at 125 °C. Ulteriorly, the activation energy values of dehydrogenation and rehydrogenation of MgH2 decrease to 70.5 ± 7.8 kJ/mol and 35.8 ± 3.8 kJ/mol on account of the presence of 10 wt% Zr0.4Ti0.6Co/5 wt% CNTs, which reasonably explains the remarkable reduction of the temperature for hydrogen sorption. Furthermore, the MgH2 + 10 wt% Zr0.4Ti0.6Co /5 wt% CNTs composite shows excellent cycling performance, indicative of potential application in practical hydrogen storage in the nearest future.

Prioritising interventions for sustainable structural transformation in Africa: a structural equation modelling approach

ABSTRACTDevelopment paradigms offer competing theories on the drivers of structural transformation. Most of the analysis has so far focused on the economic factors with little emphasis placed on either the social or environmental dimensions of sustainable development. Furthermore, there has been little theoretical or empirical analysis of how the three dimensions (e.g. economic, social, and environmental) interact to impact on structural transformation. This leaves an important gap in the literature since the three sectors are interlinked, not mutually exclusive, and hence cannot be analysed in isolation from one another. Using a panel data set for a group of 29 African countries spanning the period 1995–2011, this study employs a structural equation modelling approach to estimate the direct and indirect impacts of social, economic and environmental indicators on a composite index of structural transformation. We find that strategies that prioritise investments in social inclusion programmes have the greatest catalytic effect in advancing structural transformation in Africa.

Catalytic hydrothermal deoxygenation of the lipid fraction of activated sludge

The need for sustainable wastewater treatment and search for cheap feedstock for renewable energy production have driven investigators to evaluate the potential of producing biofuels from waste materials such as sewage sludge. The current work is aimed at assessing the potential for producing hydrocarbons from the lipid fraction of activated sludge via a catalytic hydrothermal decarboxylation reaction under varying residence time. Impacts of platinum on carbon (Pt/C) and palladium on carbon (Pd/C) catalysts were evaluated at 290 °C and residence time of 0.5, 1, 3 and 4 h. The analyses of the lipids and hydrocarbons were done using high-temperature gas chromatography. The results show that at the optimum conditions of 1 h, 290 °C, 20 mg of catalyst, 100 mg of lipid extract and 15 mL of water, the maximum yield of hydrocarbon was 23.2% of pentadecane obtained using Pt/C. This shows that the dominant hydrocarbon is pentadecane and that Pt/C exhibited greater catalytic effect than did Pd/C. The hydrocarbons might be used directly as renewable diesel and as such will contribute to the mitigation of climate change since emission of greenhouse gases will be reduced, and the use of activated sludge as the feedstock is expected to help minimize the cost of production and to ensure sustainable wastewater treatment.

Bimetallic nanomaterials as nanocatalysts and the carrier coupling chemiluminescence aptamer strategy for cancer cell detection

Cu/Co bimetallic nanomaterials (BNMs) were synthesized firstly. The chemiluminescence (CL) catalytic properties of BNMs were investigated systemically. Experimental results revealed that combined Cu with Co could cause a 67.9 ± 3.5% increase in the CL intensity because of a great synergic catalytic effect. Based on this interesting phenomenon, a steric hindrance strategy for cancer cell detection was fabricated. BNMs were used as nanocatalysts and the carrier modified with capture DNA. In presence of CCRF-CEM cell, sgc8 aptamer and probe DNA recognized with CCRF-CEM. And the bio bar code CCRF-CEM cells were formed. After bio bar code CCRF-CEM cells hybridized with capture DNA which modified Cu/Co BNMs, CL probe was introduced. The CL intensity is linearly related to the concentration of cell from 500 to 100,000 cells/mL. The detection limit is 270 cells/mL and the relative standard deviation is 3.9% at a level of 1000 cells/mL (n = 9). This method was successfully applied to the determination of cell in spiked real human serum. Due to its sensitivity and selectivity, this method offers a promising approach for the detection of cell and other biomolecules.

Selective Voltammetric Determination of Sulfur-Containing Amino Acids in Drugs and Vitamin Complexes on an Electrode Modified by a Ruthenium-Hexachloroplatinate Film

An inorganic film of ruthenium hexachloroplatinate (RuPtCl6) deposited on the surface of a glassy-carbon electrode exhibited catalytic activity for oxidation of S-containing amino acids. Catalytic electrochemical oxidation of cysteine, cystine, and methionine occurred at various potentials. The optimum conditions for producing a RuPtCl6 film that gave the greatest catalytic effect were found. A method for selective voltammetric determination of cysteine, methionine, and cystine at an RuPtCl6-film electrode was developed. The lower limit of quantitation of cysteine and cystine was 5 × 10–6 M; of methionine, 5 × 10–7 M. The proposed voltammetric method was used to determine cysteine, cystine, and methionine in drugs and vitamin complexes.

Gas generation and its isotope composition during coal pyrolysis: The catalytic effect of nickel and magnetite

Pyrolysis experiments were conducted at 370–550 °C for 72 h in closed gold capsules to investigate the effect of nickel and magnetite on gas generation from coal in the absence and presence of water.Nickel had a great catalytic effect on the yield, molecular and carbon and hydrogen isotope composition of generated gases. The methane yields increased significantly while heavy hydrocarbon gas yields decreased substantially due to the catalysis of nickel both in the absence and presence of water. The nickel catalysis caused an increase of δ13CCH4 value in the absence of water and a decrease of δ13CCH4 value in the presence of water. Results of molecular and carbon isotopic composition of hydrocarbons indicate that nickel could catalyze the decomposition of high-molecular-weight organic matter and Fischer-Tropsch-type (FTT) reactions both of which were responsible for the increased methane yield. FTT reactions catalyzed by transition metals are an important pathway for methane generation, especially in the presence of water. The catalytic decomposition of organic matter and FTT reactions also caused an increase of δ2HCH4 value both in the presence and absence of water. CO2 yield and 13CCO2 value increased obviously in the presence of nickel due to the catalytic decomposition of organic matter.In experiments without added water, addition of magnetite enhanced CO2 yield at all temperatures but only enhanced methane yield slightly at high temperature (430–550 °C). The increased CO2 and methane yields can be attributed to the oxidative decomposition of long-chain hydrocarbons via redox reactions between magnetite and hydrocarbons. In experiments with added water, addition of magnetite only caused a slight increase of methane and CO2 yields at 500 °C and 550 °C but did not influence their yields at 370–450 °C, indicating that water inhibited the effect of magnetite on methane and CO2 generation at low temperature. The addition of magnetite did not have systematic influence on carbon and hydrogen isotopes of hydrocarbon gases and carbon isotopes of CO2. Generally, the influence of magnetite on gas generation was very small.

Effects of Periplasmic Chaperones and Membrane Thickness on BamA-Catalyzed Outer-Membrane Protein Folding

The biogenesis of outer-membrane proteins (OMPs) in gram-negative bacteria involves delivery by periplasmic chaperones to the β-barrel assembly machinery (BAM), which catalyzes OMP insertion into the outer membrane. Here, we examine the effects of membrane thickness, the Escherichia coli periplasmic chaperones Skp and SurA, and BamA, the central subunit of the BAM complex, on the folding kinetics of a model OMP (tOmpA) using fluorescence spectroscopy, native mass spectrometry, and molecular dynamics simulations. We show that prefolded BamA promotes the release of tOmpA from Skp despite the nM affinity of the Skp:tOmpA complex. This activity is located in the BamA β-barrel domain, but is greater when full-length BamA is present, indicating that both the β-barrel and polypeptide transport-associated (POTRA) domains are required for maximal activity. By contrast, SurA is unable to release tOmpA from Skp, providing direct evidence against a sequential chaperone model. By varying lipid acyl chain length in synthetic liposomes we show that BamA has a greater catalytic effect on tOmpA folding in thicker bilayers, suggesting that BAM catalysis involves lowering of the kinetic barrier imposed by the hydrophobic thickness of the membrane. Consistent with this, molecular dynamics simulations reveal that increases in membrane thinning/disorder by the transmembrane domain of BamA is greatest in thicker bilayers. Finally, we demonstrate that cross-linking of the BamA barrel does not affect tOmpA folding kinetics in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes, suggesting that lateral gating of the BamA barrel and/or hybrid barrel formation is not required, at least for the assembly of a small 8-stranded OMP in vitro.

WO<sub>3</sub>:TiO<sub>2</sub> Particle Characterization Obtained by High Energy Milling for Application in Photocatalysis

Effective ways to treat textile industrial effluents have been studied in attempt to find alternatives to reduce the imminent risk of water resources contamination. The heterogeneous photocatalysis stands out in this scenario working in the organic waste mineralization, such as dyes. The objectives of this study were to investigate the obtaining of fine powders of the WO3:TiO2 (the investigated proportions in this work were 0: 100; 30:70; 50:50; 70:30; 100:0) using the high energy milling technique and to evaluate the photocatalytic efficiency of the Rhodamine B dye in this system. The oxides precursors were characterized by X-ray diffraction, BET and Helium pycnometry. After dry milling for 4 hours, the obtained powders were characterized by X-ray diffraction and tested to the photocatalysis in UV-C. The results indicate that the milling process has a direct influence on the photocatalytic properties of the investigated systems, and that the greater presence of titania in the mixture leads to a greater catalytic effect.

Catalytic hydrogenation of anthracene in ethanol

The results of the hydrogenation of anthracene in ethanol in the presence of different catalysts (the nanosized powders of Fe, Cu, and β-FeOOH and Ni and Fe supported on carbon microspheres) are reported. The greatest catalytic effect was observed upon the introduction of 1.5% Fe nanopowder.

Degradation of dimethylformamide on the surface of the nanosized WO3 films studied by infrared spectroscopy

Here I report on the degradation of dimethylformamide on the surface of the nanosized WO3 films under the action of light. Dimethylformamide, a substance that has a series of interesting properties, was adsorbed on the surface of the WO3 films and its adsorption mechanism and transformations under the action of light have been investigated with the help of the IR spectroscopy. The spirit of the research is that both DMF modifications have been used i.e., conventional and that with the substitution of hydrogen atoms by deuterium. Formation of two weak bonds (donor-acceptor bond and hydrogen bond) provides a great catalytic effect for photo-initiated proton-coupled electron transfer from the adsorbed molecules to the WO3 film surface. The mechanism of the detachment of hydrogen atoms and subsequent transformation of the adsorbed molecules has been investigated and discussed.

Dehydrogenation mechanism of ball-milled MgH2 doped with ferrites (CoFe2O4, ZnFe2O4, MnFe2O4 and Mn0.5Zn0.5Fe2O4) nanoparticles

Ferrites (CoFe2O4, ZnFe2O4, MnFe2O4 and Mn0.5Zn0.5Fe2O4) nanoparticles can all significantly reduce the desorption temperature of MgH2, and CoFe2O4 shows the best catalytic performance among the four ferrites. After dehydrogenation, new by-products including Mg, Co3Fe7 and MgO phases are found for the CoFe2O4 doped samples, and Mg, Fe3Zn10, Fe and MgO phases are identified for the ZnFe2O4 doped samples. Mg, Fe, Mn and MgO phases are observed for the MnFe2O4 doped samples, while Mg, Fe3Zn10, Mn, Fe and MgO phases appear for the Mn0.5Zn0.5Fe2O4 doped samples. New forming phases Co3Fe7, MgO and Co also have a great catalytic effect on the MgH2 hydrogen storage properties. The onset desorption temperature of MgH2 doped with bimetallic catalysts (20wt.% Co+20wt.% MgO and 20wt.% Co3Fe7+20wt.% MgO) is lower than that of MgH2 doped with the single catalyst (40wt.% Co, 40wt.% MgO and 40wt.% Co3Fe7), indicating that MgO and Co or MgO and Co3Fe7 have the combination catalytic function.

Voltammetric Determination of Acyclovir in Drugs Using an Electrode Modified by Ruthenium Hexachloroplatinate or Hexacyanocobaltate Film

A voltammetric method for determining acyclovir using a chemically modified electrode with catalytic properties was developed. The catalytic properties for acyclovir oxidation of glassy-carbon electrodes modified by inorganic films of Ru(III) hexachloroplatinate or hexacyanocobaltate were compared. The catalytic effect was manifested as a decreased potential and multiply increased oxidation current at the proposed film electrodes. The greatest catalytic effect was observed using an electrode with a film of Ru(III) hexachloroplatinate. The catalytic current depended linearly on the analyte concentration in the range from 0.5 μM to 5 mM. The proposed method was used to determine acyclovir in drugs.

Amperometric Detection of Allopurinol in Flow-Injection Analysis on Electrodes Modified by Carbon Nanotubes and Mixed-Valence Ruthenium and Iridium Oxides

Mixed-valence oxides of ruthenium (RuOx) and iridium (IrOx) and a composite based on them (IrOx—RuOx) exhibited catalytic activity for allopurinol oxidation when electrodeposited on the surfaces of unmodified glassy-carbon electrodes and those modified with functionalized single-walled carbon nanotubes (SWCNT). The greatest catalytic effect was observed on the electrode modified with composite IrOx—RuOx—SWCNT. A flow-injection method for amperometric detection of allopurinol at the modified electrode was developed. The analytical signal was linearly dependent on allopurinol concentration in the range 1 10 –6 –5 10 –3 M.

Significantly improved dehydrogenation of ball-milled MgH2 doped with CoFe2O4 nanoparticles

CoFe2O4 nanoparticles are added to magnesium hydride (MgH2) by high-energy ball milling in order to improve its hydriding properties. The hydrogen storage properties and catalytic mechanism are investigated by pressure-composition-temperature (PCT), differential thermal analysis (DTA), X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The nonisothermal desorption results show that the onset desorption temperature of the MgH2 + 7 mol% CoFe2O4 is 160 °C, which is 200 °C lower than of the as-received MgH2. The dehydrogenation process of the MgH2 doped with the CoFe2O4 nanoparticles includes two steps. DTA curves and XRD patterns reveal that a chemical reaction happens between MgH2 and CoFe2O4, forming the final products of the ternary combination, corresponding to Co3Fe7, MgO and Co. The onset desorption temperature of the ball-milled MgH2 doped with Co3Fe7, MgO and Co is about 260 °C, approximately 100 °C lower than the un-doped MgH2, demonstrating that the ternary combination (Co3Fe7, MgO, and Co) also has a great catalytic effect on the MgH2 hydrogen storage properties. It is also confirmed that the various methods of adding the ternary combination have different effects on the MgH2 hydriding–dehydriding process.