Synthesis and electrocatalytic reactivity for water oxidation of two cerium complexes

Two cerium complexes with and without manganese ion, [MnCe₄(dipic)₆(H₂O)₂₀][Ce(dipic)₃]₂·7H₂O (dipic = dipicolinate) (1) and [Ce₂(H₂O)₄(O₂CMe)₆][Ce(H₂O)₄(NO₃)₂(O₂CMe)]₂·2H₂O·2MeOH (2), have been prepared, and their electrocatalytic reactivity for water oxidation has been investigated. Compound 1 is a heterometallic 3d-4f compound which possesses four Ce(IV) ions, two Ce(III) ions, and one Mn(II). Compound 2 is composed of three neutral parts, one of which is a dinuclear cerium molecule lying on an inversion center, and the other two are symmetric monomer units; the four cerium ions in 2 are all Ce(III). Electrochemical studies of 1 and 2 show that 1 can catalyze water oxidation at the potential ~1.5 V with an overpotential of ca. 900 mV versus NHE. Control potential electrolysis (CPE) experiments at 1.50 V of 1 displayed a stable current density of 2.5 mA/cm², and the calculated Faradaic efficiency is 60%. However, no electrocatalytic reactivity was observed for 2. By comparison experiments, it was found that the electrocatalysis of 1 may result from the cooperative catalytic effect of the 4f cerium ion and 3d transition metal manganese ion.     

Synthesis of palladium–polypyrrole nanocomposite and its electrocatalytic properties in the oxidation of formaldehyde

Three alternative methods were developed for the synthesis of modifying palladium–polypyrrole layers on the surface of an inert electrode. Their electrocatalytic activity toward formaldehyde under inert atmosphere was checked. All the suggested methods are one-stage and allow synthesis of a film on the electrode surface from a solution containing a palladium salt and pyrrole in the absence of other active reagents. The electrochemical methods (potentiodynamic and double cathodic and anodic pulses techniques) in an aqueous medium give films with poorly reproducible electrocatalytic properties, while the chemical redox synthesis affords films with reproducibly high electroactivity toward methylene glycolate.     

Determination of stability constant of ternary surface complexes at liquid-solid interface in sea water by the rule of left-right shifts of S-shaped curve

A new method is suggested for determining the stability constant of ternary surface complexes (TSC) at liquid-solid interfaces in natural water. Its basic principle is based on the rule of left-right shift (RLRS) of S-shaped curve, from which the peak-type curve of E(%) with the concentration of organic matter is obtained. The peak-type curve is further used to obtain the (ksAM/kSM) values by using respectively the method of equality of E(%) when [H2A] = [H2A]0 (1) and the method of [H2A]max (2). From the known KSM,the stability constant KSAM of liquid-solid interfacial ternary surface complexes can be obtained.     

Preparation of carbon supported Pd–P catalyst with high content of element phosphorus and its electrocatalytic performance for formic acid oxidation

The carbon supported Pd–P (Pd–P/C) anodic catalyst in direct formic acid fuel cell (DFAFC) was prepared with a novel phosphorus reduction method. The Pd–P/C catalyst obtained possesses the high content of P⁰ in the alloying state. Because alloying P⁰ could decrease the 3d electron density of Pd and the adsorption affinity of CO and H on Pd, alloying P⁰ would promote the formic acid (FA) oxidation through the direct pathway. Therefore, the electrocatalytic performance of the Pd–P/C catalyst for the FA oxidation is much better than that of the Pd/C catalyst.     

Surface oxidation and water desorption of CdS

The surface oxidation and HP desorption of powder CdS were studied by means of X-ray photoetectron spectroscopy (XPS), quadrupole mass spectrometry (QMS) and in-situ FTIR. The results show that with the changes of surface composition and the elongation of store time of CdS there are four types of H2O thermally desorbed at different temperatures. It has also been found that through high-temperature air treatment for a short time the oxidized surface layer of CdS can prevent O2 and H2O in air from further attacking the inner CdS molecules.     

Determination of the emanation coefficient and the Henry’s law constant for the groundwater radon

The radon emanation coefficient (ε) from aquifer rock and the Henry’s law constant (H) of radon were determined by measuring activity concentrations using liquid scintillation counter (LSC). For the evaluation of the method, the coefficients were measured at 0, 10 and 20 °C and the temperature dependency of the coefficients was compared with others. The radon emanation coefficients from the rock particles used in this work are 0.0845, 0.1007 and 0.1308 at 0, 10 and 20 °C, respectively. The dimensionless Henry’s law constants for the groundwater used in this work are 0.994, 1.153 and 2.641 at 0, 10 and 20 °C, respectively. The results show a good agreement with those in literatures.     

Preparation of magnetite and its decomposition of water

The optimum conditions were studied for the formation of magnetite by the air oxidation of Fe(OH)2 suspensions. The cation-deficient magnetite (Fe3-δO4, δ>0) was obtained by the air (200mL/min) oxidation of Fe(OH)2 suspensions for 8- 25 h at 343 -358 K and NaOH/FeSO4=2.0 (mole ratio). The oxygen-deficient magnetite (Fe3+δO4, δ>0) was prepared through CO gas reduction of the cation-deficient magnetite at 563 K and its stableness at various temperatures and atomspheres was surveyed. The activity of decomposing water into hydrogen gas with oxygen-deficient magnetite at 563 K was studied and its relations to the oxygen-deficient degree and reaction temperature were investigated, respectively. The results show that the longer the time for magnetite being reduced by carbon monoxide, the higher the oxygen-deficient degree, and the more active its dedcomposition of water is. After reaction, oxygen (O2-) was taken away from water by oxygen-deficient magnetite, which converted to the cation-deficient magnetit     

Iron porphyrin-modified electrodes: influence of the method of modification on the stability and electroactivity in oxidation of sulfite or hydrogensulfite in ethanol–water solutions

The aim of this work is to study four types of modification of a glassy carbon electrode by Fe(III)-tetrakis(p-tetraaminophenyl)porphyrin and determine the influence of the method of immobilization of the complex on glassy carbon in electrocatalytic properties for the sulfite and hydrogensulfite oxidation in ethanol–water. The first modification was deposition of a drop of solution containing the porphyrin on a glassy carbon electrode and evaporation of the solvent (dry-drop method). The second method was immersion of the electrode at 54°C in a solution of dimethylformamide containing the porphyrin for 2 h. The third method consisted of the same heating treatment but after formation of a chemical bond of 4-aminopyridine on the glassy carbon surface, which acts as an axial ligand for the first layer of porphyrin. The fourth method involves electropolymerization of the porphyrin on the electrode surface. Important differences in stability, the potential where the oxidation wave begins and selectivity of the electrode to sulfite or hydrogensulfite were observed. The behavior of the polymer-modified electrode is different in water compared to ethanol–water.     

Determination of the stoichiometry and stability constants of theβ-cyclodextrin-dextromethorphan inclusion complexes by liquid chromatography and UV spectroscopy

The inclosion of dextromethorphan (DMN) by -cyclodextrin (-CD) was studied by using chromatography, UV spectroscopy and circular dichroism methods at 25 °C, pH 7.4 and 4.2. It was found that the CD : DMN complex has 1 : 1 stoichiometry. It is more stable at pH 7.4 than at pH 4.2. with constants respectively equal to 8000 ± 800 M^–1 and 5750 ± 500 M^–i, as determined by chromatography. The stability of the complex at pH 7.4 decreases as the temperature increases. From the van 't Hoff dependence the standard entropy and enthalpy changes were determined at this pH.     

Statistical quantification of the influence of material properties on the oxidation and ignition of activated carbons

The influence of material properties on the reactivities of activated carbon materials have been studied on a laboratory scale. Carbon samples having diversified origin and properties were characterized using a thermogravimetry (TG) coupled with a differential scanning calorimetry (DSC). Reactivity parameters like the Point of Initial Oxidation (PIO) representing the beginning of the oxidation reactions and the Spontaneous Ignition Temperature (SIT) where the bed combustion takes place in a self sustaining manner were experimentally determined. The intrinsic properties of the activated carbons influencing oxidation and ignition were examined qualitatively followed by quantitative statistical correlations. Results from both qualitative and statistical correlations showed that increase in the oxygen content in the form of surface oxygenated groups increased the reactivity of activated carbons. It was by far the single most influential property discriminated from the analysis. The porosity characteristics like the specific surface area and pore volume did show some vague trends but could not be validated like that of the oxygen content. The effects of these individual properties on the oxidation and ignition reactivity are discussed.     

Study on the variation of intraionic distance between Fe3+ and F− in methanol-water system based on its stability constant

The stability constants, ₁, of the monofluoride complex of Fe(III) have been determined in mixed methanol + water solvent system with 0.3 mol·dm^–3 HClO₄ using a solvent extraction technique. The values, in less than 0.31 mole fraction of CH₃OH (X _s) in the mixed CH₃OH+H₂O solvent solution, increase asX _s increases. The variation of in ₁ againstX _s was analyzed to elucidate the variation of intraionic distance between Fe³⁺ and F^–. The intraionic distance maintains constant inX _s<0.05 and lengthens with an increase ofX _s in 0.05<X _s<0.31.     

Electrodeposited nanostructured Pt–Ru co-catalyst on graphene for the electrocatalytic oxidation of formaldehyde

The electrochemical oxidation of formaldehyde over graphene surfaces modified with Pt–Ru co-catalyst is presented. Graphene was chemically converted from graphite and Pt–Ru co-catalyst was electrochemically deposited using cyclic voltammetry. The hybrid surface is prepared using “green approaches” and displayed electrocatalytic activity towards formaldehyde in the form of current oscillations. The current oscillations that were mainly due to adsorption/desorption of carbonaceous oxidative products are a factor of several parameters such as the concentrations of both formaldehyde and supporting electrolyte in solution, the amount of catalyst loading, scan rate of potential, upper potential limit, and the temperature change. CCG/Pt–Ru exhibited higher electrocatalytic activity toward formaldehyde electro-oxidation, and intense electrochemical current oscillations were obtained at relatively low HCHO concentrations compared to other work mentioned in literature for CCG/Pt–Pd.     

Thermal stability of phosphorus-containing styrene–acrylic copolymer and its fire retardant performance in waterborne intumescent coatings

Phosphorus-containing styrene–acrylic copolymers are synthesized by free radical seeded emulsion polymerization with the monomers of MMA/St/BA/MAA and phosphorus-containing vinyl monomer (SIPOMER PAM100). The properties of copolymer films are characterized by water adsorption test, thermogravimetry, Fourier transform infrared spectroscopy (FTIR), and energy dispersive spectroscopy (EDS), etc. The copolymer emulsions are used as the binder in an intumescent coatings formulation, and the fire-retardant performances of the coatings are determined by an instrument which the furnace temperature is analoging the cellulose fire temperature. The water adsorption of copolymer film increases remarkably owing to the increasing of phosphoric acid group in the polymer chain. The thermal decomposition stability and thermal-oxidative decomposition stability of the copolymer are improved when PAM100 is introduced into its chain, which is strongly supported by the FTIR and EDS results of copolymer residual treated at different temperature. The EDS results also illustrate that the fire retardancy enhanced by PAM100 during combustion owing to the condensed-phase mechanism. The fire-retardant test results show that the intumescent coatings using StA-P_1.5 copolymer emulsion as the binder obtains the best fire retardant performance. We suggested that StA-P_1.5 presents the lower reactivity with the acid source (APP) in 275–400 °C, and the higher reactivity with APP when the temperature is greater than 500 °C would be benefit for the swelling–charring process and the final fire retardant performance. The exorbitant crosslinking in StA-P₇ brings a negative effect on the fire-retardant performance of intumescent coatings, even if it introduces a densy swollen char layer.     

Effects of emulsifier on the bonding performance and freeze–thaw stability of starch-based wood adhesive

In this study, different emulsifiers were used to improve the bonding performance and freeze–thaw stability of renewable starch-based wood adhesive. The improved bonding performance and freeze–thaw stability were supported by the enhanced shear strength, grafted parameters, and viscosity stability after repeated freeze–thaw cycling. ζ-Potential determination, differential scanning calorimetry and pulsed nuclear magnetic resonance analysis indicated that the emulsifiers improve the grafting of vinyl acetate monomers into the starch bonds via free radical vinyl polymerization and hinder the aggregation of starch molecules. Among the emulsifiers tested, sodium dodecyl sulfate showed the highest improvement in the bonding performance and freeze–thaw stability of starch-based wood adhesives.     

Synthesis,characterization and electrochemical investigation of a new inorganic–organic hybrid compound constructed by Keggin-type polyoxometalate and cyanoguanidine

An inorganic–organic hybrid complex [HDCD]₃[PW₁₂O₄₀]·3H₂O (1) (DCD = 2-cyanoguanidine) has been synthesized from the reaction of Keggin polyanion and cyanoguanidine (C₂N₄H₄) under mild condition, and characterized by using elemental analysis, infrared spectrum, thermogravimatric analysis and single crystal X-ray diffraction. X-ray crystallography reveals that 1 displays an inorganic–organic hybrid frameworks constructed by [PW₁₂O₄₀]³⁻ Keggin-type polyoxoanion and three {(HDCD)}⁺ monocationic hydrogen-bonded units. The electrochemical behavior and electrocatalysis of 1 have been studied in detail.     

A study of the electrocatalytic oxidation of methanol on a nickel–salophen-modified glassy carbon electrode

Nickel–salophen-modified glassy carbon electrodes prepared by transferring one drop of Ni–salophen complex solution on the electrode surface. This modified electrode has been used for the electrocatalytic oxidation of methanol in alkaline solutions with various methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The electrooxidation was observed as large anodic peaks, and early stages of the cathodic direction of potential sweep around 20 mV vs. Ag|AgCl|KCl_sat. A mechanism based on the electrochemical generation of Ni (Ш) active sites and their subsequent consumptions by methanol have been discussed. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 M concentration, charge transfer resistance of nearly 0.936 kΩ was obtained, while the resistance of the electrocatalyst layer was about 111.6 Ω.     

PtIr–WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

In this article, we characterized tungsten oxide-decorated carbon-supported PtIr nanoparticles and tested it for the electrooxidation reactions of ethylene glycol and ethanol. Phase and morphological evaluation of the proposed electrocatalytic materials are investigated employing various characterization techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical diagnostic measurements such as cyclic voltammetry, chronoamperometry, and linear sweep voltammetry revealed that the tungsten oxide-modified PtIr/Vulcan nanoparticles have higher catalytic activity for ethylene glycol and ethanol electrooxidation than that of PtIr/Vulcan. A significant enhancement for electrooxidation of CO-adsorbate monolayers occurred in the presence of a transition metal oxide relative to that of pure PtIr/Vulcan electrocatalyst. The likely reasons for this are modification on the Pt center electronic structure and/or increasing the population of reactive oxo groups at the PtIr/Vulcan electrocatalytic interface in different potential regions.     

In vitro antioxidant activity of the water and ethanol extracts of Forsythia koreana flowers

The antioxidant activities of the water and ethanol extracts of F. koreana flowers were evaluated using DPPH, superoxide anion (?O(-2)), and nitric oxide (?NO) radical scavenging activity assays. The SC(50) values of the water extract of F. koreana on DPPH, ?O(-2) and ?NO were 48.39, 24.36 and 100.21 μg mL(-1), respectively. The SC(50) values of the ethanol extract of F. koreana on the aforesaid free radicals were 57.50, 49.00 and 146.08 μg mL(-1), respectively. Further, the total phenolic contents of both extracts were determined and expressed as milligram gallic acid equivalent (GAE) per gram of extract. The water extract exhibited a higher phenolic content (113.78 mg GAE?g(-1)), while the ethanol extract showed 94.53?mg GAE?g(-1). Our findings demonstrate that the water and ethanol extracts of F. koreana flowers might be potential natural sources of antioxidative additives for use in the food and other allied industries.