Redox and catalytic properties of new polypyrrole modified electrodes functionalized by [Ru(bpea)(bpy)H2O] complexes; bpea=N,N′-bis(2-pyridylmethyl)ethylamine, bpy=2,2′-bipyridine

New ruthenium(II) complexes containing one or two pyrrole-functionalized polypyridylic ligands have been prepared in order to study their electrochemical behaviour in heterogeneous phase, after anodic polymerization from CH₂Cl₂ solution on an electrode surface. Complexes containing one pyrrole unit have general formula [Ru(bpea-pyr)(bpy)(L)]²⁺ (bpea-pyr=N-[3-bis(2-pyridylmethyl)aminopropyl]pyrrole, bpy=2,2′-bipyridine, L=Cl, complex 3, or L=H₂O, complex 1), whereas compounds having two pyrrole units correspond to [Ru(bpea-pyr)(bpy-pyr)(L)]²⁺ (bpy-pyr=4-methyl-4′-pyrrolylbutyl-2,2′-bipyridine, L=Cl, complex 4, or L=H₂O, complex 2). Upon oxidative polymerization, all complexes form highly stable polypyrrolic films on a graphite disk electrode surface. An electrode modified with complex 2 polypyrrole coating film, C/poly-2, has been tested as heterogeneous catalyst for the oxidation of benzyl alcohol, showing a remarkably high efficiency and notably improving the results obtained with analogous complexes in homogeneous phase.     

On the adsorption and redox catalysis of the oxalate anion and oxalato complexes on gold and metal-modified gold electrodes

The influence of foreign metal deposits (both upd- and opd-deposits) on a gold electrode on the rate of the redox reaction iron(II)/(III) oxalate has been studied with AC impedance measurements. An attempt has been made to rationalise observed changes in the rate of reaction in terms of changed metal-redox reactant interactions. Results obtained so far do not indicate significant changes in the adsorptive interaction as evidenced with Surface Enhanced Raman Spectroscopy despite the fact, that metal-adsorbate bands are pronounced. No correlations between band positions and their changes and changes of the catalytic activity could be observed.     

In situ Raman spectroelectrochemical study of redox processes at poly(Toluidine blue) modified electrode

Electrooxidation of hydroquinone and ascorbic acid at a gold electrode modified with electropolymerized layer of phenothiazine dye Toluidine blue (PTB) has been studied with the use of in situ Raman spectroelectrochemical technique, surface enhanced resonance Raman spectroscopy (SERRS). It was shown that the redox state of PTB at any electrode potential can be determined in pH 1.0 and 4.0 solutions following specific changes in Raman spectra of these modifier layers. Electrooxidation of hydroquinone at PTB modified electrode in pH 1.0 solution, and of ascorbic acid in pH 4.0 solution, proceed without any detectable changes in a net redox state of modifier layers. It has been concluded that, under the conditions studied, both anodic oxidation processes occur most probably at the modifier/electrolyte interface rather than within the modifier film, as opposed to electrooxidation of same species at polyaniline modified electrodes studied earlier.     

Electrocatalytic properties of NDGA and NDGA/FAD hybrid film modified electrodes for NADH/NAD redox reaction

The fabrication of monolayers composed of nordihydroguaiaretic acid (NDGA), and hybrid films composed of NDGA-flavin adenine dinucleotide (FAD) adsorbed films was performed in neutral aqueous solutions to produce electrochemically active thin films exhibiting one and two redox couples, respectively. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of the NDGA and hybrid NDGA/FAD film monolayers. The NDGA modified film electrocatalytically oxidized NADH, ascorbic acid, dopamine, and N₂H₄ in neutral aqueous solutions. Well-separated voltammetric peaks were observed for dopamine and uric acid mixtures, and also for ascorbic acid and uric acid mixtures using the NDGA/GC modified electrode. When transferred to various aqueous buffered solutions, the two redox couples of the NDGA/FAD hybrid film and their formal potentials were observed to be pH-dependent. The electrocatalytic oxidation and reduction of NADH and NAD⁺ by a NDGA/FAD hybrid film in neutral aqueous solutions was carried out, and the electrocatalytic oxidation of NADH was performed using a NDGA/FAD hybrid film.     

Electrocatalytic oxidation of chlorophenols by electropolymerised nickel(II) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes

This work reports on the use of nickel(II) tetrakis benzylmercapto (NiTBMPc) and dodecylmercapto (NiTDMPc) metallophthalocyanine complexes films on gold electrodes for the electrochemical oxidation of 4-chlorophenol (4-CP) and 2,4,5-trichlorophenol (TCP). Both NiTBMPc and NiTDMPc complexes were successfully deposited on gold electrodes by electropolymerisation. The films were electro-transformed in aqueous 0.1 M NaOH solution to the ‘O-Ni-O oxo’ bridged form. For both complexes, films with different thickness were prepared and characterised by electrochemical impedance and UV-vis (on indium tin oxide) spectroscopies and the results showed typical behaviour for modified electrodes with increasing charge transfer resistance values (R_p) with polymer thickness. The poly-Ni(OH)NiPcs showed better catalytic activity than their poly-NiPcs counterparts.     

Co3O4-chitosan/biomass-derived porous carbon molecularly imprinted polymer integrated electrode for selective detection of glucose

The detection of glucose (Glu) is of great significance in medical diagnosis, food processing and biotechnology. Rapid, accurate and convenient detection technology is particularly important. Herein, the Co₃O₄-PC nanocomposite grown on biomass-derived porous carbon (PC) was prepared by hydrothermal method and subsequent air calcination. Chitosan (CS) was electrodeposited on the surface of Co₃O₄-PC by potentiostatic deposition with Glu as the template molecule. Finally, the template molecule was eluted by cyclic voltammetry to create specific recognition sites for Glu, and a highly selective and stable Glu sensor was constructed. The obtained MIP (molecularly imprinted polymer)-Glu-CS/Co₃O₄/PC nanocomposites were characterized by scanning electron microscopy, Raman spectroscopy, cyclic voltammetry, chronoamperometry and so on. The results showed that the MIP-Glu-CS/Co₃O₄-PC had great catalytic performance for Glu detection with a linear range of 12.17 μM-2.3 mM, a detection limit of 4.01 μM, and a sensitivity of 407.5 μA cm^?2 mM^?1. The sensor has excellent selectivity and stability. This work provides a guide for improving the selectivity of nanozymes.     

Influence of the preparation conditions on the properties of gold catalysts for the oxidation of glucose

In this work, two deposition–precipitation methods for the preparation of gold catalysts for glucose oxidation were investigated. Thus far, gold colloids immobilized on carbon have been used for catalytic glucose oxidation, but the long-term stability of these systems was not sufficient. To improve the long-term stability we used the deposition–precipitation methods using NaOH (DP NaOH) or urea (DP urea) as precipitation agents as they were described by Haruta and Dekkers, respectively, using alumina as a support material. With these methods, it was possible to prepare highly active and selective catalysts which showed an excellent long-term stability. DP urea was found to be the preferred method, because in contrast to DP NaOH, no losses of gold occurred during the preparation, and it was possible to adjust various gold contents up to 10 wt% Au.     

A study of the electro-catalytic oxidation of methanol on a cobalt hydroxide modified glassy carbon electrode

Cobalt hydroxide modified glassy carbon electrodes (CHM/GC) prepared by the anodic deposition in presence of tartrate ions have been used for the electro-catalytic oxidation of methanol in alkaline solutions where the methods of cyclic voltammetery (CV), chronoamperometry (CA) and impedance spectroscopy (IS) have been employed. In CV studies, in the presence of methanol the peak current of the oxidation of cobalt hydroxide increase is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of methanol is being catalysed through the mediated electron transfer across the cobalt hydroxide layer comprising of cobalt ions of various valence states. A mechanism based on the electro-chemical generation of Co(IV) active sites and their subsequent consumptions by methanol have been discussed and the corresponding rate law under the control of charge transfer has been developed and kinetic parameters have been derived. In this context the charge transfer resistance accessible both theoretically and through the IS studies have been used as a criteria. Under the CA regimes the reaction followed a Cottrellian behaviour.     

Electrodeposited MnO2/Au composite film with improved electrocatalytic activity for oxidation of glucose and hydrogen peroxide

The major drawback of currently used MnO₂ film sensor is the loss of electrical conductivity due to the formation of a poorly conductive MnO₂ layer. To overcome this problem, a coating in which the Au is alloyed with MnO₂ has been developed. The fabrication of the codeposited film electrode of Au and MnO₂ by using a cyclic voltammetric (CV) method was described, and systematic physical and electrochemical characterization was performed. This MnO₂/Au film electrode enhanced MnO₂ electrocatalytic activity. The oxidation process of glucose at the codeposited MnO₂/Au shows a well-defined peak at 0.27 V in alkaline aqueous solution. In contrast, the glucose oxidation at Au modified glassy carbon electrode (GCE) just shows a shoulder wave at 0.42 V. The experimental results indicate that the modification of MnO₂ on the surface of GCE significantly improved the electrocatalytic activity towards the oxidation of glucose. Further study shows that the MnO₂/Au could also effectively catalyze the oxidation of hydrogen peroxide in pH 7.0 phosphate buffer solution (PBS).     

Spin-glass behavior and redox catalytic properties of room temperature produced ZnCrMnO4

Recognizing the multifunctional capability of spinels, synthesis, and properties of oxide spinel with an equal concentration of Jahn Teller active Mn³⁺ and geometrically frustrated Cr³⁺ with non-magnetic Zn²⁺ have been explored. ZnCrMnO₄, resulting from the room temperature oxidation reaction, has an average crystallite size of 16 nm. Nearly 25% of Zn occupies the octahedral sites along with Cr and Mn, as revealed by the successful structural refinement in the Fd-3m space group. Electron microscopic results confirm cubic spinel formation. Raman spectrum shows the disordered nature of the spinel. X-ray photoelectron spectral (XPS) analysis establishes mixed valences of manganese ((III), (IV)) and chromium ((III) and (VI)). ZnCrMnO₄ displays electronic transitions typical of Mn³⁺ and Cr³⁺ in its UV–Visible diffuse reflectance spectrum. Spin-glass frustration at 26 K, followed by an antiferromagnetic ordering at 10 K, is noticed for the sample from the magnetic measurements. The sample exhibits a surface area of 138 m²/g (BET measurements) and catalyzes the oxidation of aromatic alcohols (phenol, benzyl alcohol) and reduction of nitroaromatics efficiently.     

Copper-decorated carbon nanotubes based composite electrodes for non-enzymatic detection of glucose

ABSTRACT: The aim of this study was to prepare three types of multi-wall carbon nanotube (CNT)-based composite electrodes and to modify their surface by copper electrodeposition for non-enzymatic oxidation and determination of glucose from aqueous solution. Copper decorated multi-wall carbon nanotube composite electrode (Cu/CNT-Epoxy) exhibited the highest sensitivity to glucose determination. The reliability of the Cu/CNT-Epoxy electrode was verified by application of this composite electrode for the determination of glucose in real blood serum samples.     

Electrocatalytic properties of new active ternary ferrite film anodes for O2 evolution in alkaline medium

Some ternary ferrites with molecular formula, CoFe_2−xCr_xO₄ (0≤x≤1.0) have been synthesized at 70 °C by a precipitation method and were transformed into the film form at the pretreated Ni support (1.5×1.0 cm²) using an oxide-slurry painting technique. The study showed that Cr-substitution from 0.2 to 1.0 mol increased the electrocatalytic activity of the oxide towards the oxygen evolution reaction (OER), the optimum improvement in apparent electrocatalytic activity being with 0.8 mol Cr. At E=600 mV versus Hg/HgO in 1 M KOH (25 °C), the apparent oxygen evolution current density (j_a) with the catalyst, CoFe_1.2Cr_0.8O₄, was ∼80 times greater than that observed with the base oxide (i.e. CoFe₂O₄). The OER on Cr-substituted oxides showed two Tafel slopes, one (b=42±1 mV per decade) at low overpotential and the other (b=66±6 mV per decade) at higher potential. The reaction order with respect to OH⁻ concentration was ∼1.3±0.1 for each electrocatalyst. The thermodynamic parameters for the OER, namely, standard apparent electrochemical enthalpy of activation (ΔH°_el^#), standard enthalpy of activation (ΔH°^#) and standard entropy of activation (ΔS°^#) have also been determined. It was observed that values of the ΔH°_el^# and ΔH°^# decreased with Cr-substitution in the CoFe₂O₄ lattice; the decrement, however, being the greatest with 0.8 mol Cr. The ΔS°^# values were largely negative varying between ∼−61 and −126 J deg⁻¹ mol⁻¹.     

Supramolecular assembly of porphyrin bound DNA and its catalytic behavior for nitric oxide reduction

A stable Fe(4-TMPyP)-DNA-PADDA (FePyDP) film was prepared on pyrolytic graphite electrode (PGE) through the supramolecular interaction between water-soluble iron(III) meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (Fe(4-TMPyP)) and DNA template, where PADDA (poly(acrylamide-co-diallyldimethylammonium chloride)) is employed as a co-immobilizing polymer. Electronic absorption spectral and quartz crystal microbalance measurements revealed that Fe(4-TMPyP) interacted with DNA to generate a species with the molar ratio of 1:5 for Fe(4-TMPyP):DNA phosphate. Cyclic voltammetry of FePyDP film showed a pair of stable and reversible peaks corresponding to Fe^III/Fe^II redox potential of −0.13 V versus Ag|AgCl in pH 7.4 PBS. The electron transfer was expected across the double-strand of DNA by an “electron tunneling” mechanism. The modified electrode displayed an excellent catalytic activity for NO reduction at −0.61 V versus Ag|AgCl. The catalytic current was enhanced at lower pH. Chronoamperometric experiments demonstrated a rapid response to the reduction of NO with a linear range from 0.1 to 90 μM. The detection limit was 30 nM at a signal-to-noise ratio of 3.     

异羟肟酸过渡金属络合物在乙苯氧化中的催化性能研究

研究了 N-苯甲酰 -N-苯基羟胺 ( BPHA)类过渡金属络合物在乙苯均相氧化中的催化行为 ,考察了络合物催化剂中心金属离子、配体结构以及添加助剂对络合物催化性能的影响 ,并找到了催化剂、助剂的最佳使用浓度及氧化反应的最适宜温度。结果表明 ,中心金属离子的电子结构对络合物催化性能影响最大 ,其活性顺序为 :Cu( BPHA) 2 >Co( BPHA) 2 >Fe( BPHA) 2>Mn( BPHA) 2 >Ni( BPHA) 2 ,配体结构对催化性能有一定影响 ,配体的芳环上有吸电子基团时 ,催化剂分解氢过氧化物的能力增加 ,主要分解产物为苯乙酮。添加轴配体对氧化反应及催化剂的选择性有较大影响 ,其中含端羟基的非环冠醚类及大环冠醚对氢过氧化物的生成和分解都有加速作用 ,含氮助剂吡啶对氧化反应有抑制作用     

Theory of linear sweep/cyclic voltammetry for the electrochemical reaction mechanism involving a redox catalyst couple attached to a spherical electrode

The catalytic mechanism O_ad + ne⁻ ? R_ad, , involving a redox couple (O_ad, R_ad) attached to the electrode, and soluble species (C_sol, D_sol), is a precursor for many contemporary electrocatalytic reaction models. The theory of cyclic voltammetry for this mechanism was presented long ago for planar electrodes. Analogous rigorous theory for spherical electrodes has not been available thus far, despite the fact that the use of spherical microelectrodes for kinetic studies is often advantageous. By adopting the integral equation formalism, combined with the recently developed adaptive Huber method for integral equations, we obtain such a rigorous theory. The theory is applicable for any value of the electrode radius r₀, from planar electrodes (r₀ → ∞), to ultramicroelectrodes (r₀ → 0). With the decreasing electrode radii the current functions increase, gradually approaching steady-state sigmoidal waves. Equations for the dependences of the forward peak potentials on dimensionless model parameters, and equations for steady-state voltammograms, obtained in this work, can be used for model verification and parameter estimation.     

Electrochemical properties of benzylmercapto and dodecylmercapto tetra substituted nickel phthalocyanine complexes: Electrocatalytic oxidation of nitrite

Nickel tetrakis(benzylmercapto)phthalocyanine (NiTBMPc) and nickel tetrakis(dodecylmercapto)phthalocyanine (NiTDMPc) complexes were synthesized and their spectral and electrochemical properties reported. The CV showed four or five redox processes for NiTBMPc and NiTDMPc, respectively. For the first time, spectroelectrochemistry gave evidence for the formation of Ni^II/Ni^I process in a NiPc complex. The rest of the processes were ring based. The NiTBMPc complex was successfully deposited on both gold and glassy carbon electrodes by electropolymerisation while NiTDMPc complex was deposited on gold electrode only. The films were electro-transformed in aqueous 0.1 M NaOH solution to the O–Ni–O oxo bridged form. The modified electrodes were characterized using electrochemical impedance spectroscopy and the results showed typical behavior for modified electrodes. Electrodes with poly-Ni(OH)Pcs films exhibited higher charge transfer resistance values, R_p than their corresponding poly-NiPcs films counterparts. All the modified electrodes showed improved catalytic activities than the unmodified electrodes towards nitrite ions electrooxidation. Better catalytic activities were observed for the modified electrodes when they were transformed to O–Ni–O oxo bridge form. All the modified electrodes exhibited high resistance to electrode surface passivation.     

Novel iron meso-nitrooctaethylporphine complexes for the catalytic reaction of alkanes with molecular oxygen

Introducing nitro groups into themeso-positions of a metalloporphyrin converts a catalytically inactive complex into a highly active catalyst for the oxidation of alkanes with molecular oxygen. The degree of nitration correlates with both the Fe(III)/Fe(II) reduction potential and the catalytic activity.     

Viscoelastic and swelling properties of glucose oxidase loaded polyacrylamide hydrogels and the evaluation of their properties as glucose sensors

Here we report the immobilization of glucose oxidase in polyacrylamide hydrogels carried out by aqueous crosslinking copolymerization of acrylamide and N,N′ methylene bisacrylamide in the presence of the enzyme. The swelling and viscoelastic properties of the hydrogels were evaluated as a function of the content of crosslinker of the polymer chains and enzyme concentration. Amperometric measurements were also carried out to evaluate the system as a glucose biosensor.     

Synthesis and catalytic oxidation properties of polymer‐bound cobalt complexes

Polymer‐bound 2,2′‐bipyridine cobalt complexes PSBPY‐Co, PSBPY‐Co‐bipy, PSBPY‐Co‐oxine, and PSBPY‐Co‐phen (where PSBPY: polystyrene bound‐2,2′‐bipyridine; bipy: 2,2′‐bipyridine; phen: 1,10‐phenanthroline) were synthesized and investigated by IR, X‐ray photoelectric spectroscopy, thermogravimetry–differential thermal analysis, inductively coupled plasma atomic emission spectrometry, and elemental analysis. The complexes were found to be catalysts for the oxidation of alkylbenzenes and cyclohexene in the presence of molecular oxygen in the absence of solvent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1068–1074, 2000     

希夫碱类金属配合物催化剂催化氧化烯烃研究进展

分析了希夫碱金属配合物的结构特点及其催化氧化烯烃的研究现状,阐述了用于均相催化氧化的希夫碱、固载型希夫碱金属配合物催化剂的分类及其在氧化烯烃领域的应用研究。通过分析希夫碱类小分子金属配合物催化氧化烯烃的缺陷,得出非均相的负载型希夫碱类金属配合物催化剂是目前主要发展方向的结论。