Oxygen reduction reaction on carbon-supported palladium nanocubes in alkaline media

Carbon-supported Pd nanocubes with the size of 30, 10 and 7 nm were prepared and their electrocatalytic activity towards the oxygen reduction reaction (ORR) in alkaline solution was studied. For comparison carbon-supported spherical Pd nanoparticles and commercial Pd/C catalyst were used. The catalysts were characterised by transmission electron microscopy, electro-oxidation of carbon monoxide and cyclic voltammetry and the ORR activity was evaluated using the rotating disk electrode method. The ORR on all studied Pd/C catalysts proceeded via four-electron pathway where the rate-limiting step was the transfer of the first electron to O₂ molecule. The specific activity of Pd nanocubes was more than two times higher than that of spherical Pd nanoparticles and increased with increasing the particle size.     

Unsupported palladium nanoparticles for ethanol cyclic voltammetric sensing in alkaline media

Carbon-supported palladium nanostructures have had a recent rise in their use for ethanol oxidation applications. In this work, we present the use of unsupported palladium nanoparticles (PdNPs), synthesized by sodium borohydride chemical reduction method, for ethanol electrochemical sensing. The unsupported PdNPs were studied for ethanol oxidation in alkaline media by cyclic voltammetry, and additionally were characterized using transmission electron microscopy, and x-ray photoelectron spectroscopy. The performance of unsupported PdNP-modified glassy carbon electrodes for the electrochemical ethanol oxidation in 1.0 M potassium hydroxide (KOH) solution was studied by cyclic voltammetry. These electrochemical results demonstrated that the unsupported PdNPs have very promising catalytic activity towards the oxidation of ethanol in alkaline media with good detection performance in the concentration range of 2304 to 288 ppm (i.e., 50.00 to 6.25 mM). The detection limit and linear correlation coefficient were 49.3 ppm (1.10 mM) and 0.9998, respectively. The unsupported PdNP-modified glassy carbon electrodes presented good cyclic voltammetric stability for ethanol sensing application in alkaline media.     

Effect of atomic-layer-deposited TiO2 on carbon-supported Ni catalysts for electrocatalytic glycerol oxidation in alkaline media

Thin TiO₂ layers were deposited onto a carbon-supported Ni catalyst (Ni/C) through atomic layer deposition (ALD) and the resulting TiO₂-coated Ni/C (ALD(TiO₂)-Ni/C) was utilized for electrochemical glycerol oxidation in alkaline media. X-ray photoelectron spectroscopy analysis demonstrated that the Ni surface phase of ALD(TiO₂)-Ni/C mainly consisted of Ni(OH)₂ while that of uncoated Ni/C was a mixed phase of NiO and Ni(OH)₂. The ALD(TiO₂)-Ni/C exhibited electrocatalytic activity at least 2.4 times higher than that of Ni/C. Density functional theory calculations were used to investigate how the modified Ni surface with the TiO₂ coating affects the adsorption/desorption of glycerol.     

Stability of small mesoporous silica nanoparticles in biological media

In this work, sub-50 nm pegylated mesoporous silica nanoparticles prepared with hydrothermal treatment are shown to have long-term stability in various media at both room and physiological temperature. Compared to bare mesoporous silica nanoparticles, the highly pegylated mesoporous silica nanoparticles show significantly improved biocompatibility and decreased macrophage uptake, making these nanoparticles viable for in vivo stealth drug delivery applications.     

Platinum nanoparticles coated by graphene layers: A low-metal loading catalyst for methanol oxidation in alkaline media

Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC). Here, we present a procedure to create a nanostructural graphene-platinum(Gr Pt) composite containing a small amount(5.3 wt%) of platinum nanoparticles coated with at least four layers of graphene. The composite, as Gr Pt ink, was deposited on a glassy carbon electrode and its electrocatalytic activity in a methanol oxidation reaction(MOR) was evaluated in a 1 M CH_3 OH/1 M Na OH solution. The results indicated an enhanced catalytic performance of Gr Pt towards MOR in alkaline media compared with the Pt/C material. Electron energy-loss spectroscopy and X-ray photoelectron spectroscopy(recorded before and after the electrochemical assays) were employed to analyze the changes in the chemical composition of the nanomaterial and to explain the transformations that took place at the electrode surface.Our findings suggest that growing of graphene on platinum nanoparticles improve the catalytic performance of platinum-graphene composites towards MOR in alkaline media.     

A kinetic study of the chlorination of tertiary alcoholamines in alkaline media

The kinetics of the chlorination of various tertiary alcoholamines by hypochlorite have been studied in alkaline media. A reaction mechanism consistent with the experimental results is put forward, and a relationship is established between the rate constants and the polar parameter (Σσ*) of the substituents.     

Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.     

Electrooxidation of ethanol on carbon nanotubes–nickel nanoparticles composites in alkaline media

In this report, the preparation of carbon nanotubes–Ni nanoparticles composites (CNT–Ni) is presented. The morphology and elemental composition of CNT–Ni composites were examined by transmission electron microscopy and X-ray diffraction. The electrochemical behaviour of carbon nanotubes–Ni nanoparticles composites in an aqueous solutions of alkali and alkaline solutions of ethanol has been studied by linear sweep voltammetry. The peak on the potentiodynamic curve for CNT–Ni composite electrode in alkaline solutions of ethanol is observed which is ascribed to the ethanol oxidation in alkaline medium. The results obtained are discussed from the point of view of employment of the CNT–Ni composites for the catalytic electrodes of fuel cells.     

High-throughput kinetic study of hydrogenation over palladium nanoparticles: combination of reaction and analysis

The hydrogenation of 1-acetylcyclohexene, cyclohex-2-enone, nitrobenzene, and trans-methylpent-3-enoate catalyzed by highly active palladium nanoparticles was studied by high-throughput on-column reaction gas chromatography. In these experiments, catalysis and separation of educts and products is integrated by the use of a catalytically active gas chromatographic stationary phase, which allows reaction rate measurements to be efficiently performed by employing reactant libraries. Palladium nanoparticles embedded in a stabilizing polysiloxane matrix serve as catalyst and selective chromatographic stationary phase for these multiphase reactions (gas-liquid-solid) and are coated in fused-silica capillaries (inner diameter 250 microm) as a thin film of thickness 250 nm. The palladium nanoparticles were prepared by reduction of palladium acetate with hydridomethylsiloxane-dimethylsiloxane copolymer and self-catalyzed hydrosilylation with methylvinylsiloxane-dimethylsiloxane copolymer to obtain a stabilizing matrix. Diphenylsiloxane-dimethylsiloxane copolymer (GE SE 52) was added to improve film stability over a wide range of compositions. Herein, we show by systematic TEM investigations that the size and morphology (crystalline or amorphous) of the nanoparticles strongly depends on the ratio of the stabilizing polysiloxanes, the conditions to immobilize the stationary phase on the surface of the fused-silica capillary, and the loading of the palladium precursor. Furthermore, hydrogenations were performed with these catalytically active stationary phases between 60 and 100 degrees C at various contact times to determine the temperature-dependent reaction rate constants and to obtain activation parameters and diffusion coefficients.     

A study of catalyst selectivity with polymer bound palladium phosphine complexes on various solid phase synthesis supports

A peptide based ligand system is synthesized on six different supports and then examined for the ability of its palladium complex to catalyze the addition of dimethylmalonate to 3-acetoxycyclopentene in six different solvents. The results on support are correlated to the results observed with the catalyst system dissolved in solution.     

Pd nanoparticles dispersed on solid supports: synthesis,characterization and catalytic activity on selective hydrogenation of olefins in aqueous media

Two types of Pd nanoparticle catalysts were prepared having 2–4 nm particle size using silica gel and porous polymer beads as solid supports. 2‐Pyridinecarboxaldehyde ligand was anchored on commercially available 3‐aminopropyl‐functionalized silica gel followed by Pd metal dispersion. Bead‐shaped cross‐linked poly(4‐vinylpyridine‐co‐styrene) gel was prepared by an emulsifier‐free emulsion polymerization of 4‐vinylpyridine, styrene and divinylbenzene in the presence of ammonium persulfate and subsequently dispersing the Pd metal on the synthesized polymer. These catalysts were characterized by SEM, TEM and ICP techiniques with respect to appearance, size and possible leaching out, respectively. Furthermore, the reactivity of these catalysts was tested on hydrogenation of various α,β‐unsaturated carbonyl compounds using aqueous solvent under a hydrogen balloon (1 atm). The results showed that the Pd dispersed on silica was a more efficient catalyst than Pd dispersed on polymer and the former could be recycled more than 10 times without considerable loss in activity. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media

Honeycomb-like porous carbons (PCs) were synthesized using a facile self-assembly method with phenolic resin as the carbon source and tetraethyl orthosilicate (TEOS) as the silica source. The PCs were found to have a large BET surface area of 458 m² g^?1 and a partially graphitized structure. The obtained PCs were used as a support for various Pt-Pd bimetallic alloy catalysts employed for methanol oxidation in alkaline media. Compared with Pt supported on commercial Vulcan XC-72R carbon (Pt/C) and with the other Pt-Pd bimetallic alloy catalysts on PCs, Pt₃Pd₁ on PCs displayed the most negative onset potential for methanol oxidation and the highest steady-state current (2.04 mA cm^?2). This may be because the Pt₃Pd₁/PCs catalyst has the largest electrochemical active surface area (ESA), and because adding Pd to the catalyst improves the ability of the intermediate species to tolerate oxidation. The results show that the prepared Pt-Pd/PCs is a potential candidate for application as a catalyst in alkaline direct methanol fuel cells.     

On the reactivity of innercomplex-bonded palladium : A new specific test for cyanides in alkaline solutions

It has been found that the innercomplex salts of palladium with dimethylglyoxime, (benzildioxime and furildioxime), salicylaldoxime and 8-hydroxyquinolinc do not enter into redox reaction with carbon monoxide, cither in solid or in molecular dispersed form.Solutions of palladium-dimethylglyoxime and palladium-salicylaldoxime in alkali hydroxide or ammonia are masked with respect to many reactions of the palladium as well as of the organic components. In alkaline solutions, when adding alkali cyanide, demasking occurs, with the deliberation of the innercomplex forming organic components. For the processes of dissolution and demasking appropriated equations are suggested.The demasking of dimethylglyoximc in alkaline solutions of palladium dimethylglyoxime permits a new sensitive test for cyanide ion. This cyanide test seems to be appropriate for the detection of illuminating gas.Palladium hydroxyquinorate is insoluble in solutions of alkali cyanides, though it is not precipitable from cyanide containing palladium solutions. An explanation for this “false equilibrium” is suggested.     

Photodecomposition of platinum and palladium alkyls: A cidnp study

Several alkyl-palladium and -platinum compounds of the general formulae L₂MR₂ and L₂MRX have been subjected to UV irradiation. A reaction occurs in chlorinated solvents such as chloroform to yield a metal chloride and a radical pair consisting of the alkyl stemming from the organometallic compound and a solvent-derived radical. The radical pair reaction is revealed by CIDNP. The decomposition products containing one more carbon atom than expectedaccording to this mechanism can be accounted for by a novel type of rearrangement, viz. an intramolecular carbene migration. In hydrocarbon solvents alkylplatinums undergo very little reaction, but alkylpalladiums decompose homolytically.     

Analysis and applications of nanoparticles in the separation sciences: A case of gold nanoparticles

Nanometer-sized gold particles—gold nanoparticles (Au NPs)—are attracting a great deal of attention for their use in various technologies, including catalysis, optical and electronic devices, and separation science. In the emerging field of nanomaterials, the design, synthesis, and characterization of nanostructures are critical features because the manipulation of these structures has a direct effect on their resulting macroscopic properties. Nanostructures fabricated in layers on surfaces—for example, through self-assembly processes—have several potential applications in separation science. This review provides an introduction to the characterizations of Au NPs using size exclusion chromatography, high performance liquid chromatography (HPLC), and electrophoresis, and their self-assembly onto solid supports for analyses based on HPLC, gas chromatography, and capillary electrophoresis. In addition, sample concentration strategies involving the use of self-assembly approaches for surface modification of Au NPs are also discussed.     

Electron transfer between trans-dihydroxotetraoxoosmate(VIII) and thiosulfate. A kinetic study in aqueous alkaline media

The kinetics of oxidation of thiosulfate to tetrathionate by trans-dihydroxotetraoxoosmate(VIII) in aqueous alkaline media have been studied. The oxidation follows a rate expression where K_Os is the formation constant of trans-dihydroxotetraoxoosmate (VIII), and K₂ and k₃, respectively, represent the formation constants of the intermediate complex involving Os(VIII) and S₂O and its decomposition constant. The K_Os, K₂, and k₃ values have been computed to be (19.5 ± 3) dm³/mol, (6.12 ± 0.5) and (3.32 ± 0.3) × 10^?1 dm³/mol s at 303 K, and I = 0.32 mol/dm³, respectively. The rate law is consistent with a mechanism envisaging the equilibrium formation of an intermediate complex involving Os(VIII) and S₂O, followed by a rate-determining decomposition of the complex with concomitant electron transfer.     

Metallic nature and surface diffusion of CO adsorbed on Ru nanoparticles in aqueous media: A 13C NMR study

We report the first observation of the 13C nuclear magnetic resonance spectroscopy (NMR) of 13CO, adsorbed from 13CO saturated 0.5 M sulfuric acid solutions, onto the surfaces of commercial Ru-black nanoparticles. The 13C NMR spectra consist of a symmetrically broadened peak having a large isotropic shift as compared to CO adsorbed onto supported Ru catalysts. The variation of the spin-lattice relaxation rate follows Korringa behavior, indicating the metallic nature of adsorbed CO, in addition to varying across the spectrum in a Korringa-like manner. Motional narrowing of the NMR spectrum at higher temperatures, together with an additional contribution to the spin-lattice relaxation rate, indicate that adsorbed CO undergoes rapid diffusion on the particle surfaces. A two-band model analysis of the NMR results indicates that the CO adsorption bond is weaker on Ru as compared to either Pt or Pd. This is also supported by a reduction in the activation energy for CO diffusion on Ru vs either Pt or Pd nanoparticles.     

Pitting corrosion and stress corrosion cracking study in high strength steels in alkaline media

Journal of Solid State Electrochemistry - Steel reinforcement in concrete is protected from corrosion by passivation due to the high alkalinity of the cement pore solution, but the presence of...