Compositions of silicododecamolybdate anion and palladium cation ultrathin layers: Their electrostatic synthesis and redox-transformations

Electrostatic synthesis of the silicododecamolybdate anion and palladium cation alternating layers is carried out for the first time. The layers are synthesized at glassy carbon in the sulfuric acid aqueous solution. The assembly was controlled by cyclic voltammetry. The composition allows four-fold current multiplication to the maximum. When the potential is cycled over the 0.6 to ?0.1 V (SCE) range, which corresponds to three redox-transfers in the silicododecamolybdate anion, palladium clusters or layers are formed, which behave as palladium metal phase in the composition.     

Redox Properties of Ferricyanide Ion on Layer‐by‐Layer Thin Film‐Coated Gold Electrodes; Effects of Type of Polycationic Components in the Film

The surface of a gold (Au) electrode was coated with layer‐by‐layer (LbL) thin films composed of poly(vinyl sulfate) (PVS) and different type of poly(amine)s including poly(allylamine) (PAH), poly(ethyleneimine) (PEI) and poly(diallyldimethylammonium chloride) (PDDA) and redox properties of ferricyanide ion ([Fe(CN)₆]^3?) on the LbL film‐coated Au electrodes were studied. The LbL film‐coated electrodes exhibited redox response to [Fe(CN)₆]^3? ion when the outermost surface of the LbL film was covered with the cationic poly(amine)s while virtually no response was observed on the LbL film‐coated electrodes whose outermost surface was covered with PVS due to an electrostatic repulsion between [Fe(CN)₆]^3? ion and the negatively‐charged PVS layer. The redox properties of [Fe(CN)₆]^3? ion on the LbL film‐coated electrodes significantly depended on the type of polycationic materials in the LbL film. The LbL film‐coated electrodes which had been immersed in the [Fe(CN)₆]^3? solution for 15 min exhibited redox response even in a [Fe(CN)₆]^3? ion‐free buffer solution, suggesting that [Fe(CN)₆]^3? ion is confined in the films. In the buffer solution, redox peaks were observed between +0.1 and 0.4 V depending on the type of polycations in the film. Thus, [Fe(CN)₆]^3? ion can be confined in the film and the redox potential is polycation‐dependent.     

Electrocatalytic Reduction of Nitrite by Phosphotungstic Heteropolyanion. Application for Its Simple and Selective Determination

Three couples of reversible redox peaks of the PW₁₂O₄₀^3? (PW₁₂) anion, which are composed of two one‐electron and one two‐electron processes occur in the potential range from +0.25 to ?0.7 V in aqueous solutions. The electrocatalytic reduction of nitrite has been studied by the first redox couple of the PW₁₂ anion at the surface of a carbon paste electrode. Cyclic voltammetric and chronoamperometric techniques were used to investigate the suitability of PW₁₂ anion as a mediator for nitrite electrocatalytic reduction in aqueous solution with strongly acidic concentration of H₂SO₄. Results showed that H₂SO₄ 1.00 M is the best medium for this purpose. In the optimum concentration of H₂SO₄, the electrocatalytic ability about 500 mV can be seen and the homogeneous second‐order rate constant (k_s) for nitrite coupled catalytically to PW₁₂ anion was calculated as 2.52×10³ M^?1 s^?1 using the Nicholson–Shain method. According to our voltammetric experiments, the catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 3×10^?5 to 1.00×10^?3 M. The detection limit has been found to be 2.82×10^?5 M (2σ). This method has been applied as a selective, simple, and precise method for determination of nitrite in real samples.     

The Electronic Ground State of [Fe(CO)3(NO)]−: A Spectroscopic and Theoretical Study

During the past 10 years iron‐catalyzed reactions have become established in the field of organic synthesis. For example, the complex anion [Fe(CO)₃(NO)]^?, which was originally described by Hogsed and Hieber, shows catalytic activity in various organic reactions. This anion is commonly regarded as being isoelectronic with [Fe(CO)₄]^2?, which, however, shows poor catalytic activity. The spectroscopic and quantum chemical investigations presented herein reveal that the complex ferrate [Fe(CO)₃(NO)]^? cannot be regarded as a Fe^?II species, but rather is predominantly a Fe⁰ species, in which the metal is covalently bonded to NO^? by two π‐bonds. A metal–N σ‐bond is not observed.     

Electrochemical and spectral properties of the composites of the alcian blue cationic phthalocyanine and silicododecamolybdate anions

Polylayer composite of ultrathin silicododecamolybdate anionic layers and alcian-blue cationic layers (pyrydinium version), containing up to 10 bilayers, is assembled. The synthesis was performed by repeated dipping of glass plate, whose one side was precoated with indium-tin oxide (ITO), into aqueous solutions of the silicododecamolybdenum acid and alcian blue [the layer-by-layer (LbL-) deposition]). Optical absorption spectra showed that the composite LbL-film is a mixture of the associate and monomer forms of the alcian blue cation, which electrostatically interact with the silicododecamolybdenum acid anions [SiMo₁₂O₄₀]^4?(SiMo). In a salt film, the silicododecamolybdenum-acid-to-alcian-blue interaction in the salt lattice promotes the deaggregation of the alcian blue molecules.     

Synthesis of novel perfluoroalkyl-containing polyethers

The synthesis of iodo(perfluoroalkyl)epoxides by radical addition of perfluoroalkyl iodides to allyl glycidyl ether and 1,2-epoxydec-9-ene is described. Dehydroiodination of additional products upon treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gives unsaturated products. The use of Bu₃SnH/Bz₂O₂ as a reduction reagent of iodo(perfluoroalkyl)allyl glycidyl ethers allows to save oxirane ring. Cationic polymerization of saturated or functional (with iodine or double bond) fluoroalkyl oxiranes under action of catalytic amount of BF₃^.Et₂O proceeds only on epoxide group. In case of poly(9-iod-10-(perfluoroalkyl)-1,2-epoxyalkane) iodine atoms are removed by standard zinc reduction.     

Electrocatalytic Oxidation of Dopamine at a Nanocuprous Oxide‐Methylene Blue Composite Glassy Carbon Electrode

Cuprous oxide nanowhisker was prepared by using cetyltrimethyl ammonium bromide (CATB) as soft template, and was characterized by XRD and TEM methods. The electrochemical properties of nano‐Cu₂O and nano‐Cu₂O‐methylene blue (MB) modified electrode were studied. The experimental results indicate that nano‐Cu₂O shows a couple of redox peaks corresponding to the redox of Cu(II)/Cu(I), the peak currents are linear to the scan rates which demonstrate that the electrochemical response of Cu₂O is surface‐controlled. The composite nano‐Cu₂O‐Nafion‐MB modified electrode shows a trend of decrease of peak currents corresponding to the Cu (II)/Cu (I). However, the electrocatalytic ability of nano‐Cu₂O‐MB composite film to dopamine increases dramatically. At this composite electrode, dopamine shows a couple of quasireversible redox peaks with a peak separation of 106 mV, the peak current increases about 8 times and the oxidation peak potential decreases about 200 mV as compared to that at bare glassy carbon electrode. The peak currents change linearly with concentration of dopamine from 1×10^?7 to 3.2×10^?4 mol/L, the detection limit is 4.6×10^?8 mol/L. The composite electrode can effectively eliminate the interference of ascorbic acid and has better stability and excellent reproducibility.     

Preparation of Polyelectrolyte Nanotubes by a Pressure filter-template Technique Using Microporous Anodic Aluminum Oxide (AAO) as the Template

Polyelectrolyte nanotubes of poly(sodium 4‐styrene‐sulfonate) (PSS) with cationic poly(diallyl dimethyl ammonium chloride) (PDDA) (PSS/PDDA) were fabricated by a pressure‐filter‐template technique using microporous anodic aluminum oxide (AAO) as the template. UV‐Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD) and infrared spectroscopy (FT‐IR) were applied to characterize the obtained PSS/PDDA nanotubes. The results have shown that the PSS/PDDA nanotubes exhibit an amorphous structure and have the outer diameter of 200 nm and length of 25 µm respectively, which are in good agreement with the dimensions of the AAO template pores. The wall thickness of the nanotubes may be controlled by the number of the self‐assembled layers. Formation of the nanotubes follows a layer‐by‐layer (LbL) mechanism due to the electrostatic interactions, where the SO^?₃ groups of PSS are first adsorbed on the Lewis acid sites of AAO template pores.     

Efficient Counter Electrode Manufactured from Ag2S Nanocrystal Ink for Dye‐Sensitized Solar Cells

It is generally believed that silver or silver‐based compounds are not suitable counter electrode (CE) materials for dye‐sensitized solar cells (DSSCs) due to the corrosion of the I^?/I₃^? redox couple in electrolytes. However, Ag₂S has potential applications in DSSCs for catalyzing I₃^? reduction reactions because of its high carrier concentration and tiny solubility product constant. In the present work, CE manufactured from Ag₂S nanocrystals ink exhibited efficient electrocatalytic activity in the reduction of I₃^? to I^? in DSSCs. The DSSC consisting of Ag₂S CE displayed a higher power conversion efficiency of 8.40 % than that of Pt CE (8.11 %). Moreover, the devices also showed the characteristics of fast activity onset, high multiple start/stop capability and good irradiated stability. The simple composition, easy preparation, stable chemical property, and good catalytic performance make the developed Ag₂S CE as a promising alternative to Pt CE in DSSCs.     

Electroenzymatic Nitrogen Fixation Using a MoFe Protein System Immobilized in an Organic Redox Polymer

We report an organic redox‐polymer‐based electroenzymatic nitrogen fixation system using a metal‐free redox polymer, namely neutral‐red‐modified poly(glycidyl methacrylate‐co‐methylmethacrylate‐co‐poly(ethyleneglycol)methacrylate) with a low redox potential of ?0.58 V vs. SCE. The stable and efficient electric wiring of nitrogenase within the redox polymer matrix enables mediated bioelectrocatalysis of N₃^?, NO₂^? and N₂ to NH₃ catalyzed by the MoFe protein via the polymer‐bound redox moieties distributed in the polymer matrix in the absence of the Fe protein. Bulk bioelectrosynthetic experiments produced 209±30 nmol NH₃ nmol MoFe^?1 h^?1 from N₂ reduction. ¹⁵N₂ labeling experiments and NMR analysis were performed to confirm biosynthetic N₂ reduction to NH₃.     

Novel type of heterogenized CuCl2 catalytic systems for oxidative carbonylation of methanol

A novel type of heterogenized CuCl₂ catalysts was designed for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) taking account of the plausible reaction mechanism and intermediates. To prevent severe corrosion of the reaction equipment materials due to Cl^? while keeping the catalytic activity of the homogeneous CuCl₂ catalyst, we adopted, as supports (or ligands) of CuCl₂, four polymers, bearing a 2,2′-bipyridine (bpy) or pyridine (py) unit, namely, poly(2,2′-bipyridine-5,5′-diyl) (Pbpy), poly(pyridine-2,5-diyl) (Ppy), poly(N,N′-bisphenylene-2,2′-bipyridine-4,4′-dicarboxylic amide) (Bpya), and poly(4-methyl-4′-vinyl-2,2′-bipyridine) (Pvbpy), together with one chelate compound, 8-quinolinol. The catalytic activity, stability of heterogenized CuCl₂ and their corrosivities to stainless steels were examined in the liquid-phase reaction of the oxidative carbonylation of methanol. These polymer-supported catalysts showed considerable catalytic activity and stability for the DMC synthesis. In particular, the Pbpy-CuCl₂ and Ppy-CuCl₂ catalysts exhibited high DMC yields and selectivity comparable to those of the homogeneous CuCl₂ catalyst. This high activity appears to be associated with the presence of the π-conjugated system in the polymers, which affect the redox reactions of Cu involved in the catalytic reaction. All of the polymer-supported CuCl₂ catalysts could be easily recycled after filtration, and the initial catalytic activity was maintained after three times of use. The corrosive characters of the catalysts were closely related to CuCl₂ leaching from the supports, which reflects the ability of supports to coordinate Cu. These experimental results suggest that both the electronic structure and the coordination ability of the polymer supports are key factors for the development of an effective catalytic system.     

Electrochemical behavior and assembly of tetranuclear Dawson-derived sandwich compound [Cd4(H2O)2(As2W15O56)2] on 4-aminobenzoic acid modified glassy carbon electrode

The transition metal-substituted heteropolyoxoanion, Cd₄(H₂O)₂(As₂W₁₅O₅₆)₂¹²⁻ (As₄W₃₀Cd₄), is one of the trivacant Dawson derivatives. Its redox electrochemistry has been studied in acid buffer solutions using cyclic voltammetry. It exhibited three steps of four-electron redox waves attributed to redox processes of the tungsten-oxo framework. Through layer-by-layer assembly, the compound was first successfully immobilized on a 4-aminobenzoic acid modified glassy carbon electrode surface by alternate deposition with a quaternized poly(4-vinylpyridine) partially complexed with [Os(bpy)₂Cl]^2+/+ (denoted as QPVP-Os). Thus, prepared multilayer films have been characterized by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy (UV-vis). The electrocatalytic activities of the multilayer films containing As₄W₃₀Cd₄ have been investigated on the reduction of three substrates of important analytical interests, NO₂⁻, BrO₃⁻ and IO₃⁻. And with the increase of the number of As₄W₃₀Cd₄ layers, the catalytic current towards the reduction of BrO₃⁻ was enhanced and the catalytic potential shifted positively.     

Redox cationic polymerization: The diaryliodonium salt/ascorbate redox couple

Strong Brønsted acids are produced on reduction of diaryliodonium salts containing anions of the type BF₄^?, AsF₆^?, PF₆^?, SbF₆^? by ascorbic acid and its derivatives in the presence of catalytic amounts of copper salts. The cationic polymerizations of cyclohexene oxide, tetrahydrofuran, and s-trioxane were studied using the diaryliodonium salt/ascorbate redox couple.     

Polymeric Electron Carriers

Polymers containing 1,4-dihydronicotinamide (P-NAH) alloxan (P-A), and viologen (P-V²⁺) moieties were synthesized and characterized. P-NAH reduced various organic substances such as lipoic acid, alloxan, and viologens and also immobilized quinone mediated by alloxan. P-A was reduced to the polymer-bearing alloxan radical and the dialuric acid structure without crosslinks by one- and two-electron reduction, respectively, and P-A also mediated the redox reaction occurring between aqueous and organic (water-immiscible) layers. P-V²⁺ was converted to the stable viologen radical reversibly by one-electron reduction. Electric potentials and currents on photo-reduction of P-V²⁺ and catalytic behavior of P-V²⁺ in the reduction of carbonyl compounds were examined.     

Catalytic Adsorptive Stripping Voltammetry of Molybdenum: Redox Kinetic Measurements

The electrode mechanism of Mo(VI) reduction was studied under catalytic adsorptive stripping mode by means of square‐wave voltammetry (SWV). Mo(VI) creates a stable surface active complex with mandelic acid. The electrode reaction of Mo(VI)‐mandelic acid system undergoes as one‐electron reduction, exhibiting properties of a surface electrode process. In the presence of chlorate, bromate, and hydrogen peroxide, the electrode reaction is transposed into a catalytic mechanism. The experimental results are compared with the recent theory for surface catalytic reaction, enabling qualitative characterization of the electrode mechanism in the presence of different catalytic agents. Utilizing both the method of “split SW peaks” and “quasireversible maximum” the standard redox rate constant of Mo(VI)‐mandelic acid system was estimates as k_s=150±5 s^?1. By fitting the experimental and theoretical results, the following catalytic rate constants have been estimated: (8.0±0.5)×10⁴ mol^?1 dm³ s^?1, (1.0±0.1)×10⁵ mol^?1 dm³ s^?1, and (3.2±0.1)×10⁶ mol^?1 dm³ s^?1, for hydrogen peroxide, chlorate, and bromate, respectively.     

Layer-by-layer electrochemical assembly of poly(diphenylamine)/phosphotungstic acid as ascorbic acid sensor

A layer-by-layer (LbL) film assembly was constructed that comprises alternative layers of poly(diphenylamine) (PDPA) and phosphotungstic acid (PTA). First, a layer of oxidized PDPA (referred to as PDPA(+)) was deposited by electropolymerization. Then, a layer of negatively charged PTA was deposited on the PDPA(+) layer . This processes was repeated several times to obtain multilayer LbL film (PDPA/PTA)_n, where n is the number of double layers. The LbLs were characterized by UV-Vis spectroscopy, FT-IR spectroscopy and X- ray diffraction spectroscopy. The process of formation of the LbL assembly was monitored by electrochemical methods. Electrochemical studies revealed that this LbL film possesses a remarkable electrocatalytic activity towards oxidation of ascorbic acid in neutral aqueous medium. The enhanced electrocatalytic activity of (PDPA/PTA)_n LbL film is attributed to the existence of tungsten atoms in the interlayers of PDPA.     

Influence of dopant ion and synthesis variables on mechanical properties of polypyrrole films

Oxidized, conductive poly(pyrrolylium anion) films [poly(pyrrolylium) = PP⁺ where there exists about one cation per three pyrrole rings] have been prepared electrochemically in an effort to study the effect of counteranion structure and preparation conditions on the composition, order (crystallinity), and mechanical properties of the films. The counteranion principally employed was p-toluene-sulfonate (OTs^?), although benzenesulfonate (BZs^?), p-ethylbenzene-sulfonate (EBs^?), and p-dodecylbenzenesulfonate (DBs^?) were incorporated in several polypyrrole films. It was found that the amount of OTs^? incorporated increased with increasing potential during synthesis, suggesting a parallel increase in the extent of oxidation of the polymer. Mechanical testing of the same films demonstrated that the ultimate tensile strength decreased as the electrode potential and current density during synthesis increased. X-ray diffraction indicated that the degree of order (reflected by the widths of the diffraction lines), albeit quite small, is dependent upon the anion species and synthesis conditions. Interestingly, samples with the highest degree of order exhibit the highest electrical conductivities.     

Polarographic Determination of Glycyrrhizic Acid Based on Double Enhancement Action of Surfactant and Dissolved Oxygen

ABSTRACT

A method for the determination of glycyrrhizic acid (GA) is described based on polarographic current of GA enhanced doubly by both cation surfactant (cetyl trimethyl ammonium bromide (CTMAB)), and dissolved oxygen (including oxygen-derived species). The doubly enhanced current of GA includes two additional currents. One is the increased reduction current of adsorbed GA induced by CTMAB. The other is the catalytic current of GA caused by the dissolved oxygen molecule and its derived species. In 0.1 M NaAc-Hac (pH4.7±0.1) ～ 1x10^?5 M CTMAB supporting electrolyte without deoxygenation, the enhanced current of GA is linearly proportional to its concentration in the range of 4x10^?7 M ～ 4.0x10^?6 M. The detection limit is 1.8x10^?7 M. The double enhanced current of GA in sensitivity is about 15 times higher than its reduction wave in the same acetate buffer solution.     

Electrochemical behavior of polypyrrole/ kodak aq composite polymeric films

The anodic polymerization of pyrrole (P) onto glassy carbon in an aqueous solution of the Kodak-AQ poly(ester sulfonic acid) polyelectrolyte gives a PP/AQ composite film. While incorporated as charge compensators during the anodic growth of PP, the entangled AQ⁻ chains cannot easily diffuse out upon reduction. The composite layer, resulting from such unique use of AQ ionomers (as electrolyte and dopant) possesses the features of both its conducting polymer and cation exchanger components. These include effective loading of hydrophobic cations, potential switch effect or permselective response. For example, the uptake of Ru(bpy)²⁺₃ by the AQ anion, residing in the conducting polymer, is facilitated by an electrochemical event (reduction of the film to PP⁰/AQ⁻). Similarly, the redox switchable PP component offers electrochemical control of the release of loaded cations. These and other attractive properties of PP/AQ composite layers are explored by cyclic voltammetry, chronocoulometry, potentiometry and flow injection amperometry.     

Electrocatalytic Carbon Dioxide Reduction by Using Cationic Pentamethylcyclopentadienyl–Iridium Complexes with Unsymmetrically Substituted Bipyridine Ligands

Eight [Ir(bpy)Cp*Cl]⁺‐type complexes (bpy= bipyridine, Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) containing differently substituted bipyridine ligands were synthesized and characterized. Cyclic voltammetry (CV) of the complexes in Ar‐saturated acetonitrile solutions showed that the redox behavior of the complexes could be fine tuned by the electronic properties of the substituted bipyridine ligands. Further CV in CO₂‐saturated MeCN/H₂O (9:1, v/v) solutions showed catalytic currents for CO₂ reduction. In controlled potential electrolysis experiments (MeCN/MeOH (1:1, v/v), E_app=?1.80 V vs Ag/AgCl), all of the complexes showed moderate activity in the electrocatalytic reduction of CO₂ with good stability over at least 15 hours. This electrocatalytic process was selective toward formic acid, with only traces of dihydrogen or carbon monoxide and occasionally formaldehyde as byproducts. However, the turnover frequencies and current efficiencies were quite low. No direct correlation between the redox potentials of the complexes and their catalytic activity was observed.