The 2D Rancieite-type manganic acid and its alkali-exchanged derivatives: Part I — Chemical characterization and thermal behavior

The 2D Rancieite type manganic acid was prepared by reduction of KMnO₄ in acidic medium. Its ion exchange behavior allows to prepare alkali derivatives. All compounds were characterized with use of a combination of X-ray diffraction, chemical analyses, TGA, magnetic measurements and spectroscopic techniques. The evolution of their chemical composition versus temperature was studied between 180 and 400 °C. It shows that the dehydration process is partly reversible in these compounds whereas the weak reduction is irreversible. The 2D Rancieite-type manganic acid is readily different from a Birnessite-type phyllomanganate, as shown by several features: the interlayer distance, the ion exchange capacity, the thermal behavior, the interlayer cation content, the manganese average oxidation state, the magnetic behavior and the IR spectrum.     

How photocatalytic activity of the MAO-grown TiO2 nano/micro-porous films is influenced by growth parameters?

Pure titania porous layers consisted of anatase and rutile phases, chemically and structurally suitable for catalytic applications, were grown via micro-arc oxidation (MAO). The effect of applied voltage, process time, and electrolyte concentration on surface structure, chemical composition, and especially photocatalytic activity of the layers was investigated. SEM and AFM studies revealed that pore size and surface roughness of the layers increased with the applied voltage, and the electrolyte concentration. Moreover, the photocatalytic performance of the layers synthesized at medium applied voltages was significantly higher than that of the layers produced at other voltages. About 90% of methylene blue solution was decomposed after 180 min UV-irradiation on the layers produced in an electrolyte with a concentration of 10 g l⁻¹ at the applied voltage of 450 V.     

The effect of resistant starches on fat oxidation in healthy adults as measured by a 13CO2-breath test

A resistant starch (RS) mixture (MIX) consisting of fibre of potatoes (FP) and wrinkled pea starch (WPS), and high amylose maize starch (HAMS) were supplemented in adults to evaluate their effects on fat oxidation by means of a ¹³CO₂-breath test. Sixteen subjects received a regular diet either without or with the supplementation of MIX and HAMS in randomised order. After administration of a [U-¹³C]algal lipid mixture, exhaled air was collected over 14?h in 0.5- and 1-h intervals. The ¹³C abundances were measured by nondispersive infrared spectroscopy. In comparison to the dry run (DR), supplementation with MIX and with HAMS increased the cumulative percentage dose recovery: (DR: 16.7?%, MIX: 16.9?%, HAMS: 18.0?%), but without statistical significance. The colonic degradation of MIX and HAMS to short-chain fatty acids tends to lower the formation of carbohydrate-derived acetyl-CoA and contributes to a postprandial lipid oxidation increase by using fat-derived acetyl-CoA as a compensatory fuel source.     

Effects of duty ratio at low frequency on growth mechanism of micro-plasma oxidation ceramic coatings on Ti alloy

The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti-6Al-4V alloy prepared by pulsed single-polar MPO at 50 Hz in NaAlO₂ solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. The changes of the duty ratio (D) of the anode process led to the changes of the mode of the spark discharge during the pulsed single-polar MPO process, which further influenced the structure and the morphology of the ceramic coatings. The coatings prepared at D = 10% were composed of a large amount of Al₂TiO₅ and a little γ-Al₂O₃ while the coatings prepared at D = 45% were mainly composed of α-Al₂O₃ and γ-Al₂O₃. The coating thickness and the roughness were both increased with the increasing D due to the formation of Al₂O₃. The formation of Al₂TiO₅ resulted from the spark discharge due to the breakdown of the oxide film, while the formation of Al₂O₃ resulted from the spark discharge due to the breakdown of the vapor envelope. The ceramic coatings improved the corrosion resistance of Ti-6Al-4V alloy. And the surface morphology and the coating thickness determined the corrosion resistance of the coated samples prepared at D = 45% was better than that of the coated samples prepared at D = 10%.     

High-pressure laminar flame speeds and kinetic modeling of carbon monoxide/hydrogen combustion

Laminar flame speeds were accurately measured for CO/H₂/air and CO/H₂/O₂/helium mixtures at different equivalence ratios and mixing ratios by the constant-pressure spherical flame technique for pressures up to 40 atmospheres. A kinetic mechanism based on recently published reaction rate constants is presented to model these measured laminar flame speeds as well as a limited set of other experimental data. The reaction rate constant of CO + HO₂ → CO₂ + OH was determined to be k = 1.15 × 10⁵T^2.278 exp(−17.55 kcal/RT) cm³ mol⁻¹ s⁻¹ at 300-2500 K by ab initio calculations. The kinetic model accurately predicts our measured flame speeds and the non-premixed counterflow ignition temperatures determined in our previous study, as well as homogeneous system data from literature, such as concentration profiles from flow reactor and ignition delay time from shock tube experiments.     

Surface and catalytic properties of doped tin oxide nanoparticles

Mixed oxides composed of Zn-Sn, Ti-Sn and V-Sn were prepared by a co-precipitation method and evaluated as catalysts for methanol oxidation in an ambient fixed-bed reactor. Surface analysis by X-ray photoelectron spectroscopy (XPS) revealed an electronic interaction between dopant and Sn atoms in the oxide structure and showed the formation of surface states associated with the dopants. Oxygen vacancies were present on the Zn-doped oxide, and the oxidation of methanol to carbon oxides was favored. The Ti-doped oxide exhibited a favorable selectivity to dimethyl ether, related to the oxygen anions near Ti centers. Vanadium dopants not only dramatically increased the catalytic activity but also promoted the partial oxidation of methanol to formaldehyde. Results demonstrate that the bridging dopant-O-Sn bond acts as active sites and influences product distribution.     

Theoretical study on the catalytic properties of single-atom catalyst stabilised on silicon-doped graphene sheets

ABSTRACT

The stable configurations, electronic structures and catalytic activities of single-atom metal catalyst anchored silicon-doped graphene sheets (3Si-graphene-M, M?=?Ni and Pd) are investigated by using density functional theory calculations. Firstly, the adsorption stability and electronic property of different gas reactants (O₂, CO, 2CO, CO/O₂) on 3Si-graphene-M substrates are comparably analysed. It is found that the coadsorption of O₂/CO or 2CO molecules is more stable than that of the isolated O₂ or CO molecule. Meanwhile, the adsorbed species on 3Si-graphene-Ni sheet are more stable than those on the 3Si-graphene-Pd sheet. Secondly, the possible CO oxidation reactions on the 3Si-graphene-M are investigated through Eley–Rideal (ER), Langmuir–Hinshelwood (LH) and new termolecular Eley–Rideal (TER) mechanisms. Compared with the LH and TER mechanisms, the interaction between 2CO and O₂ molecules (O₂?+?CO → CO₃, CO₃?+?CO → 2CO₂) through ER reactions (< 0.2?eV) are an energetically more favourable. These results provide important reference for understanding the catalytic mechanism for CO oxidation on graphene-based catalyst.     

Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.     

Comparison of microbiological loads and physicochemical properties of raw milk treated with single-/multiple-cycle high hydrostatic pressure and ultraviolet-C light

The effects of ultraviolet-C radiation (UV-C, 11.8?W/m²), single-cycle and multiple-cycle high hydrostatic pressure (HHP at 200, 400 or 600?MPa) on microbial load and physicochemical quality of raw milk were evaluated. Reductions of aerobic plate count (APC) and coliform count (CC) by HHP were more than 99.9% and 98.7%, respectively. Inactivation efficiency of microorganisms increased with pressure level. At the same pressure level, two-cycle treatments caused lower APC, but did not show CC differences compared with single-cycle treatments. Reductions of APC and CC by UV-C were somewhere between 200?MPa and 400/600?MPa. Both HHP and UV-C significantly decreased lightness and increased pH, but did not change soluble solids content and thiobarbituric acid-reactive substances’ values. Two 2.5?min cycles of HHP at 600?MPa caused minimum APC and CC, and maximum conductivity. Compared with HHP, UV-C markedly increased protein oxidation and reduced darkening.