Electrocatalytic activity of palladium–polypyrrole nanocomposite in the formaldehyde oxidation reaction

Palladium–polypyrrole nanocomposite materials with high electrocatalytic activity toward formaldehyde in an alkaline solution (methylene glycolate) have been synthesized via a one-step redox route. Key factors that have an effect on the sensor properties of palladium nanoparticles have been determined. It has been demonstrated for the first time that the emergence of not only the forward but also the reverse wave of formaldehyde oxidation on palladium particles is associated with the oxidation of methylene glycolate rather than intermediate species.     

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.     

Electrochemical and electrocatalytic behaviour of platinum–palladium nanoparticle alloys

The electrochemical and electrocatalytic behaviour of Pt/Pd nanoparticles prepared in water-in-oil microemulsion was reported. The catalytic activity of the nanoparticles was studied by using the reactions of dissociative adsorption of methanol and formic acid. The use of these surface probe reactions allowed the detection of palladium at the surface of the nanoparticles. The electrochemical stability of the particles was also investigated by voltammetry and electrochemical quartz crystal microbalance (EQCM). We shown that EQCM technique may be quantitatively used to correlate mass and area modifications when the electrochemical conditions produce corrosion of the elements of the alloy.     

Synthesis,structural and optical properties of tin oxide nanoparticles and its CMC/PEG–PVA nanocomposite films

Polyethylene glycol–polyvinyl alcohol (PEG–PVA) blend is a multifunctional material and controlling its properties is important for various medical and industrial uses. In this paper, we report the influence of carboxymethyl cellulose (CMC) and doping with tin oxide (SnO₂) nanoparticles (NPs) on the structural and optical properties of PEG–PVA. The prepared samples were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and UV–Vis-NIR spectroscopies. SnO₂ NPs of rutile structure, average crystallite size of ～30.2 nm and optical band gap (E_g) of 3.68 eV were prepared by a simple sol–gel process. CMC addition enhances the crystallinity of PEG–PVA that then gradually reduced by increasing SnO₂ doping ratio. The optical transmittance of PEG–PVA increased from 77 to 90% after mixing with CMC and then decreased to 64% with increasing SnO₂ content to 1.5%. Also, the E_g of PEG–PVA increased from 5.20 to 5.28 eV and then decreased to 4.88 eV due to CMC addition and SnO₂ incorporation, respectively. The refractive index, the dispersion parameters and the optical conductivity of PEG–PVA, CMC/PEG–PVA and of its nanocomposite films are discussed. The correlation between the structural modifications and the resultant optical properties are reported.     

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.     

Determination of the stability constant of cobalt-substituted mono-lacunary Keggin-type polyoxometalate and its electrocatalytic water oxidation performance

The anion form of a cobalt-substituted mono-lacunary Keggin-type polyoxometalate (POM) complex in aqueous solution was identified as [Co(H₂O)(H₃PW₁₁O₃₉)]^2? and its stability constant was determined to be 5.19 × 10⁴ by spectrophotometry. Additionally, the electrocatalytic performances toward water oxidation of different concentrations of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? were investigated in the neutral phosphate buffer solution, and it was found that [Co(H₂O)(H₃PW₁₁O₃₉)]^2? anion itself has little activity; the activity of [Co(H₂O)(H₃PW₁₁O₃₉)]^2? solution actually results from dissociated [Co(H₂O)₆]²⁺. This work provides a simple way to understand the origin of catalytic water oxidation activity of a POM-based complex.     

Construction of hyaluronan-silver nanoparticle–hemoglobin multilayer composite film and investigations on its electrocatalytic properties

In this work, hyaluronan-silver nanoparticles (HSNPs) were prepared by UV-initiated photoreduction, and protein hemoglobin (Hb) was then alternately assembled with the prepared negatively charged HSNPs into layer-by-layer (LBL) films on solid surface. The electrochemical behavior and electrocatalytic activities toward oxygen and hydrogen peroxide of the resulting films were studied. It was found that the HSNPs greatly enhanced the electron transfer reactivity of Hb as a bridge. The assembly films showed a pair of nearly reversible redox peaks with a formal potential of −0.32 V (vs. Ag/AgCl) for the heme Fe(III)/Fe(II) redox couple. The immobilized Hb in the films maintained its biological activity, showing a surface-controlled process with a heterogeneous electron transfer rate constant (k _s) of 1.0 s⁻¹ and displaying the same features of a peroxidase in the electrocatalytic reduction of oxygen and hydrogen peroxide. This work provides a novel model to fabricate LBL films with protein, polysaccharide and nanoparticles, which may establish a foundation for fabricating new type of biosensors based on the direct electron transfer of redox proteins immobilized in nanocomposite multilayer films with underlying electrodes.     

Sterically stabilized polypyrrole–palladium nanocomposite particles synthesized by aqueous chemical oxidative dispersion polymerization

Aqueous chemical oxidative dispersion polymerizations of pyrrole using PdCl₂ oxidant were conducted using water-soluble polymeric colloidal stabilizers in order to synthesize polypyrrole–palladium (PPy–Pd) nanocomposite particles in one step. PPy–Pd nanocomposite particles with number average diameters of approximately 30 nm were successfully obtained as colloidally stable aqueous dispersions, which were stable at least for 7 months, using poly(4-lithium styrene sulfonic acid) colloidal stabilizer. The resulting nanocomposite particles were extensively characterized with respect to particle size, size distribution, colloidal stability, nanomorphology, surface/bulk chemical compositions, and conductivity. X-ray photoelectron spectroscopy indicated the existence of poly(styrene sulfonic acid) colloidal stabilizer on the surface of the nanocomposite particles. Transmission electron microscopy studies confirmed that nanometer-sized Pd nanoparticles were distributed in the PPy matrix.     

Synthesis and characterization of monomeric and dimeric palladium(II)–ammonium complexes: their use for the catalytic oxidation of alcohols

The addition of quaternary ammonium salts, R₄NX, to PdCl₂ leads to mononuclear anionic complexes: (R₄N)₂PdX₄. A dinuclear complex, (n-Bu₄N)₂Pd₂Cl₆, has been characterized from the crystallization of the corresponding monomeric species under controlled conditions. These complexes revealed a similar efficiency as mixtures of PdCl₂ and R₄NX for the catalytic oxidation of alcohols using 1,2-dichloroethane as both solvent and stoichiometric oxidant.     

Effect the conditions of the acid–thermal modification of clinoptilolite have on the catalytic properties of palladium–copper complexes anchored on it in the reaction of carbon monoxide oxidation

The dependence of the physicochemical and structural–adsorption properties of natural and acid–thermal modified clinoptilolite, and of Pd(II)–Cu(II) catalysts based on them, on the duration of acid–thermal modification is investigated. The samples under study are described via XRD and thermal gravimetric (DTG and DTA) analysis, IR, DR UV–Vis, EPR spectroscopy, and water vapor adsorption. Values of both the specific surface area (S_sp) and pH of aqueous suspensions are determined. The resulting catalysts are tested in the reaction of low-temperature carbon monoxide oxidation with air oxygen. A conclusion is drawn about the nature of surface bimetallic Pd(II)–Cu(II) complexes. The greatest catalytic activity is shown by complexes based on clinoptilolite and modified with 3 M HNO₃ for 0.5 and 1 h.     

Synthesis and some properties of a new compound in the Al–Sb–V–O system

A new compound in the Al?CSb?CV?CO system of the composition AlSbVO₆ was successfully synthesized by a solid-state reaction and characterized by powder XRD diffraction. The structural and thermal properties of AlSbVO₆ were investigated. The infra-red spectrum of the new phase is presented.     

Synthesis,identification and study of electrical conductivity of the doped copolymer carbazole–phenol formaldehyde

The copolymer carbazole–phenol formaldehyde doped with 4 (4-hydroxy-phenyl azo)-benzene sulfonic acid (PABS), 2,5-dimethyl benzene sulfonic acid (PXSA) and 4-hydroxy-m-benzene disulfonic acid (PDSA) were prepared. These compounds are identified by FT-IR spectroscopy.The conductivity of copolymer carbazole–phenol formaldehyde doped with 4 (4-hydroxy-phenyl azo)-benzene sulfonic acid (PABS), 2,5-dimethyl benzene sulfonic acid (PXSA) and 4-hydroxy-m-benzene disulfonic acid (PDSA) was studied as a function of weight of the dopant compounds; an increase of conductance of the copolymer by doping with PABS is noted; the conductance became equal to 0.000595 ohm⁻¹ for 0.1 g higher conductance for the copolymer when it is doping with PABS.     

Formation of micro- and nanosized particles of the Fe–Al–Co system in water solutions and its magnetic properties

Samples of the Fe–Al–Co system are obtained electrochemically in a water solution. The kinetic dependences that describe the processes that occur in microparticles of aluminum in water solutions are established. The phase composition of the synthesized samples is determined via X-ray diffraction and Mössbauer spectroscopy. It is shown that the main contribution to the fine magnetic structure of Fe–Al–Co is made by the magnetically ordered structure with a hyperfine field around 348 kOe formed by a mechanical mixture of FeCo and Al.     

Synthesis and characterization of polypyrrole–magnetite–vitamin B12 hybrid composite electrodes

In this study vitamin B12 covered magnetite nanoparticles have been incorporated into a conducting polypyrrole. This polymer was electrochemically synthesized in the presence of the B12-coated magnetite. The adsorption of B12 was demonstrated by the decrease in absorbance of the vitamin in the supernatant liquid after B12 has been in contact with magnetite sol overnight. The composition of the layers was studied by the electrochemical quartz crystal microbalance technique during the polymerization. The slope of the mass change–charge curves indicate the incorporation of 27 m/m% magnetite and 15 m/m% B12. The redox transformation of the film in monomer- and nanoparticle-free solutions was also investigated by this method and the difference in the virtual molar masses of the moving species was evidenced. The morphology and the composition of the layers were characterized by scanning electron microscopy combined with energy dispersive X-ray microanalysis measurements, which latter proved the successful incorporation of the magnetic and bio-active components. The electrochemical behavior of the films unambiguously showed the complex redox activity of the composites and the current surplus were quantified by the redox capacity of the layers. These data show the doubling of the redox capacity in case of the hybrid material compared to the neat polymer. The successful enrichment of B12 can be exploited in the recently evidenced redox mediation process performed by a PPy/B12 film.     

Preparation,magnetic properties and microwave absorption of Zr–Zn–Co substituted strontium hexaferrite and its nanocomposite with polyaniline

Russian Journal of Applied Chemistry - M-type strontium hexaferrite substituted by Zr4+, Zn2+, and Co2+ was firstly synthesized by a sol-gel auto combustion method. Then the polyaniline/hexaferrite...     

Synthesis of ITQ-2 zeolite under static conditions and its properties

Zeolite ITQ-2 can be synthesized by swelling the layers of MCM-22 precursor. It has a single delami-nated structure of MWW with thickness of 2.5 nm. It shows disordered properties in long range and ordered in short range, which is a promising catalytic ma…