Investigation of catalytic activity of cobalt–Schiff base complex covalently linked to the polyoxometalate in the alkene and benzyl halide oxidation with hydrogen peroxide

The catalytic activity of a hybrid compound Co(salen)–POM (1) consisting of cobalt(salen) [salen = N,N′-bis(salicylidene)ethylenediamine] complex covalently linked to a Keggin type polyoxometalate (POM) was studied, for the first time, in the oxidation of various olefins in acetonitrile, using hydrogen peroxide as an oxygen source. The complex (1) can catalyze oxidation of various olefins including non-activated terminal olefins. The effect of other parameters such as solvent, oxidant and temperature were also investigated. The selective oxidation of benzyl halides to their corresponding carbonyl compounds by complex (1), as catalyst, was also examined at room temperature.     

Detonation combustion of a hydrogen–oxygen mixture in a plane–radial combustor with exhaustion toward the center

Regimes of continuous spin detonation in a plane–radial combustor with an external diameter of 80 mm with peripheral injection of a hydrogen–oxygen mixture in the range of specific flow rates of the mixture 3.6–37.9 kg/(s ·m²) are obtained for the first time. Depending on the diameter of the exit orifice in the combustor (40, 30, or 20 mm), specific flow rate of the mixture, its composition, and counterpressure, one to seven transverse detonation waves with a frequency from 6 to 60 kHz are observed. It is found that the number of detonation waves increases, while their intensity decreases owing to reduction of the exit orifice diameter or to an increase in the counterpressure. The flow structure in the region of detonation waves is analyzed. The domain of detonation regimes in the coordinates of the fuel-to-air equivalence ratio and specific flow rate of the mixture is constructed. A physicomathematical model of continuous spin detonation in a plane–radial combustor is formulated. For parameters of hydrogen and oxygen injection into the combustor identical to experimental conditions, the present simulations predict similar parameters of detonation waves, in particular, the number of waves over the combustor circumference and the wave velocity.     

Synthesis of a graphene–carbon nanotube composite and its electrochemical sensing of hydrogen peroxide

Graphene, whose structure consists of a single layer of sp²-hybridized carbon atoms, provides an excellent platform for designing composite nanomaterials. In this study, we have demonstrated a facile process to synthesize graphene–multiwalled carbon nanotube (MWCNT) composite. The graphene–MWCNT composite material is endowed with a large electrochemical surface area and fast electron transfer properties in Fe(CN)₆^3?/4? redox species. A graphene–MWCNT composite modified electrode exhibits good performance in terms of the electrocatalytic reduction of H₂O₂; a sensor constructed from such an electrode shows a good linear dependence on H₂O₂ concentration in the range of 2 × 10^?5 to 2.1 × 10^?3 mol L^?1. The detection limit is estimated to be 9.4 × 10^?6 mol L^?1. This study provides a new kind of composite modified electrode for electrochemical sensors.     

Electrochemical reduction of 2-ethyl-9,10-anthraquinone (EAQ) and mediated formation of hydrogen peroxide in a two-phase medium Part II: Production of alkaline hydrogen peroxide by the intermediate electroreduction of EAQ in a flow-by porous electrode in two-phase liquid–liquid flow

Hydrogen peroxide production by the intermediate electroreduction of the 2-ethyl–9,10-anthraquinone (EAQ) was carried out in a flow-by cell and a two-phase electrolyte formed by a mixture of tributylphosphate (TBP) and diethylbenzene (DEB) as the organic phase, and a solution of NaOH as the aqueous phase. The cathode used was a reticulated vitreous carbon (RVC) foam. We have examined the following process variables: electrolysis current (0.3–3.1A), catholyte flow rate (470–1630mlmin–1), EAQ concentration in the organic phase (0.21–0.42m), organic/aqueous phase volume ratio (1/9–4/6) and grade of porosity of the RVC (20–45ppi). The electrolyses can be carried out in the presence or absence of oxygen gas. The first method is the so-called one-step electrolysis and the second method is the two-step electrolysis. In the second method, the disodium salt of the hydroquinone (EAQNa2) is electrochemically formed in the absence of oxygen. The second step consists of the chemical reaction of this salt with oxygen to form hydrogen peroxide. We obtained a hydrogen peroxide concentration of 0.8m after 10Ah with an electrolysis current of 1.55A and a current efficiency of 70%.     

Influence of hydrogen peroxide-based bleaching agents on the bond strength of resin–enamel/dentin interfaces

This study evaluated the effect of different bleaching techniques on the bond strength of pre-existing adhesive restorations in enamel and dentin. Hydrogen peroxide-based bleaching gels with different concentrations (7.5% and 35%) were used on composite restorations of Adper Single Bond 2 (3M/ESPE, St. Paul, USA) and Filtek Z250 (3M/ESPE, St. Paul, USA). Twenty human third molars were randomly divided into 8 groups: GE—enamel control; GE7.5—bleaching using 7.5% hydrogen peroxide; GE35—bleaching using 35% hydrogen peroxide; GE 7.5+35—bleaching using 7.5% and 35% hydrogen peroxide; GD—dentin control; GD7.5—7.5% hydrogen peroxide; GD35—35% hydrogen peroxide; and GD 7.5+35—7.5% and 35% hydrogen peroxide. Bleaching was performed using long clinical application-time to low concentration gel, and short clinical application-time to high concentration gel. Unbleached specimens were stored in artificial saliva for 14 days. Specimens subject to micro-shear testing and data were analyzed by Analysis of Variance and Tukey's test (p=0.05). Enamel micro-shear bond strength was reduced after 7.5% hydrogen peroxide and after association of 7.5% and 35% hydrogen peroxide. Bleaching treatment altered dentin bond strength only when using 7.5% hydrogen peroxide. The results suggest that the bond strength of the restorations was influenced by the clinical extent of bleaching-gel application time and was not dependent on bleaching-gel concentration.     

Interplay of coordination and hydrogen bonding modes in the self-assembly of the supramolecular network in copper(II) phthalate–trimethoprim complex (0.5:1:1)

Trimethoprim cations forming self complementary hydrogen-bonded DADA arrays interact with the copper–phthalate supramolecular frameworks through extensive hydrogen bonding.     

Non-intrusive determination of bubble size in a gas–solid fluidized bed: An evaluation

Bubble sizes measured in a column of diameter 290 mm with FCC particles utilizing both an intrusive optical probe and non-intrusive pressure analysis are compared. The pressure signals were decoupled by differential pressure analysis and incoherence analysis. It is shown that pressure fluctuations induced by jetting/bubble formation can be effectively filtered out by differential pressure and incoherence analysis. The differential pressure signals measured across a vertical interval less than half the maximum bubble size unreasonably damps the power spectral density intensity, leading to underestimation of bubble size and overestimation of mean frequency. In the present work, the incoherence analysis tends to estimate greater bubble size than differential pressure analysis. Bubble chord lengths are overestimated by optical probe signals because small bubbles are not detected. Bubble sizes calculated by the equation of Horio and Nonaka (1987) agree reasonably well with that estimated by incoherence analysis at relatively high superficial gas velocities.     

Ignition of a two-fuel hydrogen–silane mixture in air

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen–air mixture in the temperature range from 1200 to 2500 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.     

Baeyer–Villiger oxidation of cyclic ketones with aqueous hydrogen peroxide catalyzed by transition metal oxides

The Baeyer–Villiger oxidation of cyclic ketones to the corresponding lactones using aqueous hydrogen peroxide as an oxidant over transition metal oxides was investigated. MoO₃ and WO₃ were found to exhibit higher catalytic activity than TiO₂, Fe₂O₃, Co₃O₄, ZnO and ZrO₂. The high catalytic activity was attributed to the interaction of MoO₃/H₂O₂ and WO₃/H₂O₂. Additionally, the reaction mechanism on MoO₃ and WO₃ was proposed.     

An experimental study of copper sulfide flotation in a packed cyclonic–static microbubble flotation column

A method using a cyclonic–static microbubble flotation column packed with fluid guiding media was proposed for improving flotation efficiency of copper sulfide. The installation of packed fluid guiding media in a cyclonic–static microbubble flotation column was for changing flow pattern in 10 the column by avoiding strong cyclonic flow in the upper region of the column, which can cause bubble-particle detachment. Therefore, the attached particles can be more likely to enter the froth zone instead of swirling in the column. The flow rectification contributed to a smaller bubble size in the column and significantly reduced the number of big bubbles with diameter above 1 mm. This scenario was caused by the damping of swirling liquid motion where bubbles tended to 15 concentrate and coalescence in the center of an eddy. The packed fluid guiding media changed the hydrodynamics in the upper column from a cyclonic flow to a gentle flow and as a result improve the column separation. The application of packed fluid guiding media can decrease the bubble-particle detachment and the flotation recovery of copper sulfide could constantly improve with the installation of packed fluid guiding media in the FCSMC column.     

Stereo-Preference in the degradation of the erythro and threo isomers of β-O-4-type lignin model compounds in oxidation processes. part 2: In the reaction with hydroxyl and oxyl anion radicals under hydrogen peroxide bleaching conditions

We examined which isomer, the erythro or threo, of non-phenolic β-O-4-type lignin model compounds is stereo-preferentially attacked by hydroxyl radical and its conjugate base, oxyl anion radical, generated by the decomposition of hydrogen peroxide in the presence of ferric ion and its precipitates under hydrogen peroxide bleaching conditions. The intrinsic stereo-preference of oxyl anion radical was slightly toward the erythro isomer, while hydroxyl radical had a further smaller stereo-preference. These stereo-preferences can be explained by our prior knowledge that oxyl anion radical preferentially attacks the side-chain of the lignin model compounds rather than the aromatic nucleus. The amount of the degraded lignin model compounds became less great with decreasing pH, but reversely and intensively greater in the pH range below 10. This phenomenon can be attributed to the change in the decomposition mechanism of hydrogen peroxide accompanying the pH variation.     

Curing of a tetrafluoroethylene–propylene elastomer with high-vinyl polybutadiene rubber and peroxide

A cocuring agent is necessary for tetrafluoroethylene–propylene elastomer (FEPM), which cannot be cured by peroxide alone. We observed that high-vinyl polybutadiene rubber (HVBR) could be used as a cocuring agent for FEPM. The structure and properties of FEPM–HVBR blend vulcanizates were investigated by ¹³C-NMR, differential scanning calorimetry, swelling tests, tensile tests, dynamic mechanical analysis, and thermogravimetric analysis. This research showed that HVBR significantly improved FEPM by conferring a high crosslink degree to the FEPM–HVBR blends. When the HVBR concentration was 25% without any filler reinforcement, the tensile strength of the FEPM–HVBR blend vulcanizate reached 11.6 MPa, and the crosslinking density reached 171 μmol/cm³. In addition, HVBR improved the thermal stability of FEPM and changed the glass-transition temperature (T _g) of the blend; as the HVBR content increased, the T _g of the blend also increased. ¹³C-NMR analysis confirmed that crosslinks existed between the HVBR and FEPM macromolecules. When the blends contained trace amounts of HVBR, free-radical reaction was more preferred between FEPM and HVBR, whereas when HVBR was 15% or more, crosslinking between HVBR was predominant. These findings expand the choices for the curing of FEPM. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47836.     

Fabrication of a novel ZnO–CoO/rGO nanocomposite for nonenzymatic detection of glucose and hydrogen peroxide

Herein, a novel nanocomposite of binary ZnO–CoO nanoparticles loaded on the graphene nanosheets (ZnO–CoO/rGO) has been successfully constructed via a facile, economical and two–step process. The obtained ZnO–CoO/rGO hybrids with high electrical conductivity and abundant active sites, could be modified on a glassy carbon electrode to detect glucose and H₂O₂ multi–functionally. The fabricated biosensor exhibits wide linear range for glucose (10 μM to 11.205 mM) and H₂O₂ (25 μM to 11.1 mM), and their corresponding sensitivity are 168.7 μA mM^?1 cm^?2 and 183.3 μA mM^?1 cm^?2. The limits of detection are 1.3 μM and 0.44 μM for the oxidation of glucose and the reduction of H₂O₂, respectively. Furthermore, remarkable selectivity, long–term stability and outstanding reproducibility of the non–enzyme biosensor prove that ZnO–CoO/rGO hybrids are the promising candidate in practical applications.     

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H₂O₂ in the linear range of 1–250 μM in lab samples, and 1 × 10⁻³–2 × 10⁻² M in real samples, respectively.     

Continuous spin detonation of a heterogeneous kerosene–air mixture with addition of hydrogen

Regimes of continuous spin detonation of two-phase kerosene–air mixtures with small addition of hydrogen are obtained for the first time in a flow-type annular cylindrical combustor 503 mm in diameter.     

Preparation and evaluation of a novel wound dressing sheet comprised of β-glucan–chitosan complex

A transparent wound dressing sheet was obtained by forming a complex between β-glucan and chitosan (CS). These materials were chosen for their biocompatible, bioabsorbable, and biodegradable properties, and they were expected to promote the therapeutic efficacy of the dressing by increasing the wound healing response. The therapeutic efficacy of the β-glucan–CS complex sheet as a wound dressing was evaluated in wounds created on the dorsal surfaces of mice. β-glucan–CS complex sheets demonstrated therapeutic efficacies comparable or superior to that of Beschitin®W, a commercial wound dressing made from CS. Additionally, the β-glucan–CS complex sheet did not dissolve during the application period, did not adhere to wounds, and was easy to remove. Cumulatively, these results indicate that β-glucan–CS complex sheets are a promising new wound dressing product.     

Electrochemical characterization of Cu dissolution and chemical mechanical polishing in ammonium hydroxide–hydrogen peroxide based slurries

Chemical mechanical polishing (CMP) of copper in ammonium hydroxide based slurry in the presence of hydrogen peroxide was investigated. The polishing trend was found to be similar to that exhibited by other slurries containing hydrogen peroxide and various complexing agents used for Cu CMP. When the hydrogen peroxide concentration is increased, the polish rate increases, reaches a maximum and then decreases. The location and the magnitude of the maximum depend on the ammonium hydroxide concentration. The dissolution of copper in the NH₄OH–hydrogen peroxide solution was probed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments. Electrical equivalent circuit (EEC) and reaction mechanism analysis (RMA) were employed to determine the mechanistic reaction pathway of Cu dissolution in NH₄OH–hydrogen peroxide system. Based on the RMA analysis, a four step catalytic mechanism with two adsorbed intermediate species is proposed.     

Synthesis and evaluation of a ruthenium–copper oxide/silica catalyst derived from microemulsion processing

Bimetallic Ru–Cu catalysts supported on SiO₂ have been synthesized in microemulsions using sodium metasilicate (Na₂SiO₃), copper nitrate (Cu(NO₃)_2·3H₂O) and ruthenium chloride (RuCl₃) at 28 °C. The microemulsion system consists of sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT) and sodium dodecyl sulphate (SDS), cyclohexane, and an aqueous solution of sodium metasilicate or metal salts. The catalysts have been characterized by XPS, EDX/SEM with line scanning and they possess a very narrow pore size distribution (around 38 Å) and relatively high specific surface areas (around 400 m²/g). The catalytic results of the N₂O decomposition reveal that higher conversions of N₂O can be achieved by the catalysts synthesized from the microemulsion process at lower temperatures (around 400 °C).