Oxidation Of Nitrite Ions Research Articles

Designing of Au doped TiO2 NPs as an electrocatalyst for nitrite sensor

In the present work, a simple ionothermal protocol for the synthesis of Au doped TiO2 and its subsequent application as an electrochemical interface for the trace level electroanalytical quantification of nitrite ion has been described. The surface morphology and the composition has been described with the help of Scanning electron microscope and Energy Dispersive X-Ray techniques. Further, it has been used in the fabrication of thin film electrodes by a simple physical drop casting method. Cyclic voltammetry has been used to decipher the electrocatalytic property of the modified interface towards nitrite ions and square wave voltammetry to work in the low concentration levels of nitrite ions. The developed sensor interface revealed superior nitrite sensing performance in the dynamic concentration range from 3.3 to 120 µM with a very low experimental detection limit of 0.095 µM with a sensitivity of 0.9973. The analytical applicability of the developed interference has been validated by determining the presence of nitrite from real samples with least interference from commonly encountered foreign ions. The stability and reproducibility of the proposed interface has been studied over a period of several months and the results were found to be highly reproducible with a relative standard deviation of ± 5 %. These results show that, the proposed interface electrode display better electrocatalytic activity compared to the previously reported sensors for the electro oxidation of nitrite ions.

Revisiting the mechanisms of nitrite ions and ammonia removal from aqueous solutions: photolysis versus photocatalysis.

Nitrite ions and ammonia are widespread forms of inorganic water pollutants. Nevertheless, the mechanisms of their photolytic and photocatalytic reactions under UV-A irradiation are still fully undisclosed, particularly, at different pH values under aerobic and inert atmospheres. Herein, we have studied the photolytic decomposition of nitrite ions under different conditions using 365nm UV-A LED as a light source instead of mercury lamps that emit photons in the UV-B region and generate a lot of heat. The results indicated that the rate of nitrite disproportionation in the dark at pH ≤ 3.0 is remarkably high relative to the rate of the photolytic decomposition. At pH ˃ 3, the photolytic reaction is negligible and nitrite ions showed considerable stability. In contrast, the photocatalytic oxidation of nitrite ions over TiO2 photocatalysts, namely, TiO2P25, TiO2UV100, and TiO2 anatase/brookite mixture proceeds at pH ˃ 3.0. TiO2 P25 exhibited the highest photocatalytic activity at pH 5. Interestingly, the photolytic simultaneous removal of nitrite ions and ammonia was possible at pH 9.0 in the absence of oxygen (Ar atmosphere). A 42.69 ± 0.66%, 27.75 ± 1.7%, and 32.74 ± 0.59% of nitrogen calculated based on nitrite, ammonia, and both of them, respectively, can be removed after 6h of UV-A irradiation. The selectivity of N2 evolution was 77.6%. The nitrogen removal rate was significantly reduced in the presence of TiO2 photocatalyst evincing that TiO2 photocatalysis is applicable for nitrite ions oxidation, whereas the photolytic process is better suited for the simultaneous removal of nitrite ions and ammonia.

Behaviour of Nitrogen Soluble Forms in Natural Water in the Presence of Anionic and Cationic Surfactants and Mineral Substrates

The redox processes, organic substances accumulation, chemical equilibria and adsorption of organic substances on the substrate surface function of natural water compositions and substrate granule sizes have been investigated. Laboratory simulations have been carried out for the Nistru and Isnovat river waters. The natural water models containing laurylsulphate (LS) as anionic surfactant (SAS An) and cetyltrimethylammonium (CTMA) as cationic surfactant (SAS Ct), separately and in a body, as well as the substrates Al(OH)3, Al2O3, CaCO3, H2SiO3, light fraction (clayey) of diatomite and expanded clay powder have been studied. The timely distribution of the soluble nitrogen species containing NH4+, NO2- and NO3- in the samples of natural waters has been analyzed. It has been found that LS diminishes the redox processes braking due to the partial fixation of toxic organic matter. Similar, but more pronounced enhancement impact on oxidation of nitrite ions as a result of fixation and sedimentation of organic components has been found in the case of the calcium carbonate powder. Also, CaCO3 produces a better SAS Ct separation/inactivation of organic part in the presence of both anionic and cationic SASs. A water self-purification processes effectiveness in polluted river waters decreases in the CaCO3, Al(OH)3, Al2O3, H2SiO3, light fraction (clayey) of diatomite, expanded clay powder substrate series.

Ozone-assisted catalytic oxidation of aqueous nitrite ions on HZSM-5 zeolites

Simultaneous removal of NOx and SO2 during the wet absorption process has made it possible for nitrogen resource utilization. However, nitrites formation at high ratio in absorption solution would limit its application. In this study, the catalytic oxidation behaviors of aqueous nitrite ions assisted by ozone on HZSM-5 zeolites with different SiO2/Al2O3 ratios have been investigated. The experimental results revealed that the oxidation and disproportionation reactions of nitrite ions took place competitively, both of which were accelerated under acidic condition. Moreover, the introduction of HZSM-5 zeolites and ozone would significantly improve the nitrite oxidation rate, where the zeolites with high SiO2/Al2O3 ratios were found to be more effective owing to the enhanced adsorption of nitrite ions and ozone. Based on the results under different operating conditions (such as O3 concentration, HZSM-5 dosage, pH values and presence of radical scavengers etc.), the reaction mechanism was then proposed. The disproportionation reaction of nitrite ions mainly occurred in the bulk solution. And the catalytic oxidation of nitrite ions over zeolites proceeded via a non-radical surface reaction between the adsorbed nitrite ions and ozone/oxygen molecular.

The usage of nitrogen compounds by purple non-sulfur bacteria of the Rhodopseudomonas genus

In this article, we characterized the regularities of oxidation of nitrite ions by phototropic purple non-sulfur bacteria Rhodopseudomonas yavorovii IMV B-7620, which were isolated from the water of Yavorivske Lake (Lviv Region, Ukraine). The bacteria were cultivated anaerobically at the light intensity of 200 lux and aerobically without illumination for 13 days in the modified ATCC No. 1449 medium. The concentration of nitrite ions was determined turbidimetrically by the turbidity of the solution by method of diazotization of sulfanilic acid by the nitrite ions and the interaction of the formed salt with n-(l-naphtyl)ethylenediamine dihydrochloride. The concentration of nitrate ions was determined turbidimetrically by the turbidity of the solution by method of diazotization. Zinc powder was used as a reducing agent. Efficiency of oxidation of 0.7–5.6 mM nitrite ions as electron donors by these bacteria was 100–7%, on the 10-th day of cultivation. It was established that nitrate ions were accumulated in the medium as a result of oxidation of nitrite ions by bacteria. The largest biomass (1.6 g/L) bacteria accumulated on the thirteenth day of growth in a medium with 2.8 mM NO2–. We found that R. yavorovii can use nitrate ions and urea as the only source of nitrogen for phototrophic growth. At a concentration of 1.9 mM ammonium chloride, sodium nitrite and urea in the cultivation medium, the biomass of bacteria was 1.2, 0.8, 1.0 g/L, respectively. The ability of the studied microorganisms to oxidize nitrite ions and to use nitrate ions indicates the significant impact of purple non-sulfur bacteria on the redistribution of streams of nitrogen compounds in ecosystems and the essential role of these microorganisms in the nitrogen biogeochemical cycle.

Fabrication of polyoxometalate/GO/PDDA hybrid nanocomposite modified electrode and electrocatalysis for nitrite ion, ascorbic acid and dopamine

Based on self-assembly and electrodepositing, a two-dimensional PMo10V2/GO/PDDA hybrid nanocomposite modified glass carbon electrode (GCE) was successfully fabricated for the first time. Graphene oxide (GO), PDDA, and PMo10V2 have been modified on GCE surface. Analysis by SEM and FTIR, GO has provided larger specific surface area for improving electrocatalysis activity of PMo10V2. The electrochemical behavior and electrocatalysis of the modified electrode were studied by detailed characterization of cyclic voltammetry (CV) and amperometric (i-t) methods. The experimental results demonstrated that PMo10V2/GO/PDDA/GCE has high stability, fast response, and good electrocatalytic activity towards the oxidation of nitrite ion (NO2−), ascorbic acid (AA), and dopamine (DA) compared to GCE, PDDA/GCE, and GO/PDDA/GCE respectively. Their concentrations are linearly proportional to the amperometric signals. The correlation coefficients of NO2−, AA, and DA are 0.999, 0.998, and 0.998 respectively. The detection limits were estimated to be 0.45 μM, 0.03 μM, and 0.18 μM for NO2−, AA, and DA with the signal to noise ratio of 3. Almost no interference effect was observed for sensing of NO2−, AA, and DA in the presence of each other. The proposed modified electrode was employed for the determination of the NO2−, AA, and DA level in human blood serum with recoveries between 97.35% and 104.2%.

Large-scale production of CdO/Cd(OH)2 nanocomposites for non-enzyme sensing and supercapacitor applications.

Recent advancements in electrode design are substantially linked to state-of-the-art nanomaterial fabrications. Herein, we report a simple one-pot hydrothermal synthesis of Cd(OH)2 with a platelet-like morphology, which was subsequently annealed at relatively high temperatures to produce a CdO/Cd(OH)2 nanocomposite for the first time. It was found that the control of thermal treatment allowed tunable charge transport across the nanometre scale due to the presence of CdO and Cd(OH)2 mixed nanocrystals. The CdO/Cd(OH)2 nanocrystals offer interesting prospects for the electrocatalytic oxidation of nitrite ions and for supercapacitor applications. The CdO/Cd(OH)2 nanocomposite was blended with a trace amount of gold NPs for enhancing the electrochemical conductivity and electrocatalytic capability for nitrite oxidation with a sensitivity of 32.9 μA mM−1. It afforded a promising electrocatalyst in a wide concentration range up to 10 mM with a low detection limit of 0.87 μM. Furthermore, the CdO/Cd(OH)2 nanocomposite electrode was showed to be a highly active and stable supercapacitor, achieving a high specific capacitance in an alkaline medium of about 145 F g−1 at a discharge current of 2.0 A g−1. These results have revealed that the presence of mixed oxide/hydroxide nanocrystals in nanoscale dimensions will be very interesting for various electrochemical applications and provide for a new class of nanodevices based on electrochemistry with unique capabilities.

Selective and Sensitive Nitrite Sensor Based on Glassy Carbon Electrode Modified by Silver Nanochains

AbstractHerein, we report a facile method for the synthesis of silver nanochains (Ag nanochains) using pyridine as growth directing agent and citrate ions as capping agents in alkaline medium. The characterization of the synthesized high aspect ratio Ag nanochains was accomplished with the help of Transmission Electron Microscopy (TEM) and High Resolution Transmission Electron Microscopy (HRTEM) which demonstrates the thickness below 100 nm. Crystalline nature of the synthesized Ag nanochains was investigated using X‐ray diffractrometry. A sensitive electrochemical nitrite sensor was assembled using synthesized Ag nanochains as electrode modifier. An improved cyclic voltammetric response for the oxidation of nitrite ions was witnessed at the modified GCE surface in comparison to bare GCE in Britton Robinson (BR) buffer (pH 4). The influence of pH on the oxidation peak current of nitrite ions was also examined using cyclic voltammetry. The electrocatalytic oxidation currents attained through amperometric measurements at Ag nanochains modified GCE were linearly dependent on the concentration of nitrite ions in the two ranges of 0.5–7.5 µM, 5–480 µM. Linear calibration plots of Ip vs. concentration of nitrite were also constructed at the proposed sensor using square wave voltammetry and differential pulse voltammetry. The proposed sensing strategy was successfully employed for the determination of nitrite in water samples with excellent recoveries.

Simultaneous pit generation and visualization of pit topography using combined atomic force–scanning electrochemical microscopy

Combined atomic force microscopy–scanning electrochemical microscopy (AFM–SECM) is for the first time used to generate single corrosion pits on passivating iron surfaces in the micrometer range. The AFM–SECM probe locally generates nitric acid during the oxidation of nitrite ions with the release of protons at selected sites on the surface of the otherwise passive metal. High confinement of passive film breakdown is achieved from the combination of a small probe size and the inhibiting properties of non-reacted nitrite ions on the surrounding passivated surface. Simultaneous visualization of pit nucleation and propagation can be obtained in the same solution without changing the probe by AFM.

Mathematical modeling and experimental study of electrode processes

The purpose of this paper is to propose mathematical modeling of different kinds of electrochemical processes. Electrooxidation of nitrite ions on some types of electrodes (glassy carbon, screen-printed carbon-containing, gold, and gold nanoparticles) and oxidation of ascorbic acid on gold electrodes nonmodified and modified by gold nanoparticles were used for the comparison of calculated and experimental data. It is shown that in each case, a specific shape of the voltammogram helps to identify the mechanism of the process. The comparison of the theoretical and experimental data shows that the process of oxidation of nitrite ions causes passivation of the electrode by adsorbed products of electrooxidation, and nanoeffects are not observed at that. Nanoeffects were observed in the oxidation of ascorbic acid on gold nanoparticles localized on gold electrode.

Electroanalysis of nitrobenzene derivatives and nitrite ions using silver nanoparticles deposited silica spheres modified electrode

An electrochemical sensor was developed for the detection of nitrobenzene derivatives and nitrite ions using silver nanoparticles (Ag NPs) deposited on amine functionalized silica (SiO2) spheres modified electrode. The electrocatalytic reduction of nitrobenzene and oxidation of nitrite ions were studied using SiO2/Ag NPs at three different Ag concentrations (1, 2 and 3mM) modified electrodes. In electrocatalysis, a positive shift in the reduction peak potential for nitrobenzene and a significant increase in the catalytic oxidation current for nitrite ions were observed at these modified electrodes. An improved electrocatalytic activity for the reduction of nitrobenzene and oxidation of nitrite ions was achieved at the SiO2/Ag (3mM) NPs modified electrode due to the large number of Ag NPs deposited on SiO2 surface. The lowest experimental detection limits of 500nM for nitrobenzene derivatives and 1μM for nitrite ions at the SiO2/Ag NPs modified electrode were observed.

Gold nanoparticles decorated on cobalt porphyrin-modified glassy carbon electrode for the sensitive determination of nitrite ion

The present study reports the electrochemical determination of nitrite ion using citrate-gold nanoparticles (cit-AuNPs) decorated on meso-tetra(para-aminophenyl)porphyrinatocobalt(II) (Co(II)MTpAP) self-assembled glassy carbon electrode (GCE). The decoration of cit-AuNPs on Co(II)MTpAP was achieved with the aid of amine groups present on the surface of the self-assembled monolayer (SAM) of Co(II)MTpAP. The SEM image shows that the cit-AuNPs were densely packed on Co(II)MTpAP. The AuNPs decorated electrode was successfully used for the determination of nitrite ion. The cit-AuNPs decorated electrode not only shifted nitrite ion oxidation potential towards less positive potential but also greatly enhanced its current when compared to bare and Co(II)MTpAP SAM modified electrodes. The amperometric current increases linearly while increasing the concentration of nitrite ion ranging from 0.5×10−6 to 4.7×10−3M and the detection limit was found to be 60nM (S/N=3). Further, the modified electrode was successfully used to determine nitrite ion in the presence of 200-fold excess of common interferents such as Na+, NO3-, I−, K+, CO32-, Ca2+, SO42-, NH4+, Cl− and glucose. The practical application of the cit-AuNPs decorated electrode was demonstrated by determining nitrite ion in water samples.

Electrochemistry of Iron-Doped Zircon and Zirconia Materials and Electrocatalytic Effects on Nitrite Oxidation and Reduction

Tetragonal and monoclinic Fe-doped solid solutions are prepared by annealing FexZr1-xO2 gels at different temperatures. Also tetragonal Fe-doped solid solution@SiO2 core-shell composites and Fe-zircon solid solutions are obtained after annealing FexZrSiO4 gels. The electrochemical response of iron-doped zirconias (FexZr1-xO2) and zircons (FexZrSiO4) attached to graphite electrodes in contact with aqueous electrolytes, is described using the voltammetry of microparticles methodology complemented by atomic force microscopy (AFM). These techniques are applied to characterize the electrocatalytic effect exerted by such materials on the reduction and oxidation of nitrite ion in aqueous media.

Electrocatalytic Activity of Carbonized Nanostructured Polyanilines for Oxidation Reactions: Sensing of Nitrite Ions and Ascorbic Acid

A comparative study of the electrocatalytic activity of nitrogen-containing carbon nanomaterials, prepared by the carbonization of nanostructured polyaniline (PANI) salts, for the electrooxidation reactions is presented. Nanostructured PANI salts were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous solution in the presence of 5-sulfosalicylic acid (PANI-SSA), 3,5-dinitrosalicylic acid (PANI-DNSA) as well as without added acid (PANI), and subsequently carbonized to c-PANI-SSA, c-PANI-DNSA and c-PANI, respectively. Glassy carbon tip was modified with nanostructured c-PANIs and used for the investigation of sensing of nitrite and ascorbic acid in aqueous solutions as model analytes by linear sweep voltammetry. All three types of the investigated c-PANIs gave excellent response to the nitrite ions and ascorbic acid electrooxidation. The lowest peak potential for nitrite ion oxidation exhibited c-PANI (+0.87V vs. SCE), and for ascorbic acid oxidation both c-PANI and c-PANI-SSA (ca.+0.13V vs. SCE). Electrochemical data were correlated with structural and textural data obtained by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, elemental and nitrogen sorption analysis.

The Effect of Freezing on Reactions with Environmental Impact

The knowledge that the freezing process can accelerate certain chemical reactions has been available since the 1960s, particularly in relation to the food industry. However, investigations into such effects on environmentally relevant reactions have only been carried out since the late 1980s. Some 20 years later, the field has matured and scientists have conducted research into various important processes such as the oxidation of nitrite ions to nitrates, sulfites to sulfates, and elemental mercury to inorganic mercury. Field observations mainly carried out in the polar regions have driven this work. For example, researchers have found that both ozone and mercury are removed from the troposphere completely (and almost instantaneously) at the time of Arctic polar sunrise. The monitoring activities suggested that both the phenomena were caused by involvement of bromine (and possibly iodine) chemistry. Scientists investigating the production of interhalide products (bromine and iodine producing interhalides) in frozen aqueous solutions have found that these reactions result in both rate accelerations and unexpected products. Furthermore, these scientists did this research with environmentally relevant concentrations of reagents, thereby suggesting that these reactions could occur in the polar regions. The conversion of elemental mercury to more oxidized forms has also shown that the acceleration of reactions can occur when environmentally relevant concentrations of Hg(0) and oxidants are frozen together in aqueous solutions. These observations, coupled with previous investigations into the effect of freezing on environmental reactions, lead us to conclude that this type of chemistry could potentially play a significant role in the chemical processing of a wide variety of inorganic components in polar regions. More recently, researchers have recognized the implications of these complementary field and laboratory findings toward human health and climate change. In this Account, we focus on the chemical and physical mechanisms that may promote novel chemistry and rate accelerations when water-ice is present. Future prospects will likely concentrate, once again, on the low-temperature chemistry of organic compounds, such as the humic acids, which are known cryospheric contaminants. Furthermore, data on the kinetics and thermodynamics of all types of reaction promoted by the freezing process would provide much assistance in determining their implications to environmental computer models.

Supramolecular Approach to Gold Nanoparticle/Triruthenium Cluster Hybrid Materials and Interfaces

AbstractA systematic and comprehensive study of the interaction of citrate‐stabilized gold nanoparticles with triruthenium cluster complexes of general formula [Ru3(CH3COO)6(L)]+ [L = 4‐cyanopyridine (4‐CNpy), 4,4′‐bipyridine (4,4′‐bpy) or 4,4′‐bis(pyridyl)ethylene (bpe)] has been carried out. The cluster–nanoparticle interaction in solution and the construction of thin films of the hybrid materials were investigated in detail by electronic and surface plasmon resonance (SPR) spectroscopy, Raman scattering spectroscopy and scanning electron microscopy (SEM). Citrate‐stabilized gold nanoparticles readily interacted with [Ru3O(CH3COO)6(L)3]+ complexes to generate functionalized nanoparticles that tend to aggregate according to rates and extents that depend on the bond strength defined by the characteristics of the cluster L ligands following the sequence bpe > 4,4′‐bpy >> 4‐CNpy. The formation of compact thin films of hybrid AuNP/[Ru3O(CH3COO)6(L)3]+ derivatives with L = bpe and 4,4′‐bpy indicated that the stability/lability of AuNP–cluster bonds as well as their solubility are important parameters that influence the film contruction process. Fluorine‐doped tin oxide electrodes modified with thin films of these nanomaterials exhibited similar electrocatalytic activity but much higher sensitivity than a conventional gold electrode in the oxidation of nitrite ion to nitrate depending on the bridging cluster complex, demonstrating the high potential for the development of amperometric sensors.

Electrocatalytic oxidation of nitrite on a carbon paste electrode modified with Co(II) porphyrin adsorbed on SiO 2/SnO 2/Phosphate prepared by the sol–gel method

This paper describes the immobilization of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphyrin ion on SiO 2/SnO 2/Phosphate obtained by the sol–gel processing method. The porphyrin was adsorbed on the surface of the modified material and furthermore metallized in situ with Co(II) ion. The porphyrin metallation process was followed using UV–Vis spectroscopy by inspecting the Q bands of the free and metallated porphyrin. A carbon paste electrode modified with material containing metallated porphyrin was used to study the electro-catalytic oxidation of nitrite ions by means of cyclic voltammetry, chronoamperometry and RDE voltammetry. The modified electrode was very stable and exhibited the electro-catalytic oxidation of nitrite ions at 0.72 V vs. SCE by a two electron mechanism producing nitrate ions at pH 5.4. The kinetic parameters of the electrode reaction process were calculated; (1 − α) n a was 0.479, D was (5.3 ± 0.11) × 10 −5 cm s −1, and k 0 could be determined as (5.4 ± 0.14) × 10 −3 cm s −1.

Electrocatalytic activity of Ce(III)–EDTA complex toward the oxidation of nitrite ion

The electrochemical behavior of Ce(III) ion in the presence of EDTA and their application for electrocatalytic oxidation of nitrite ion is described in this manuscript. The electrochemical properties of Ce(III)–EDTA complex as well as the two-electron oxidation of nitrite ion were investigated using cyclic voltammetry and hydrodynamic voltammetry methods. Kinetic parameters such as transfer coefficient, homogeneous rate constant for electrocatalytic oxidation of nitrite ion at the experimental conditions, were obtained. Also the possible mechanism for oxidation of nitrite ion using Ce(III)–EDTA complex is proposed. The detection limit of 4.8 × 10 −6 M and dynamic linear range 1.0 × 10 −5 to 1.0 × 10 −2 M were obtained for determination of nitrite ion using electrocatalytic oxidation of this ion by Ce(III)–EDTA complex.

Synthesis of new octakis(benzylthio)tetraazaporphyrin complexes with bivalent transition metal ions and an investigation of their spectral, redox and catalytic properties

Transition metals in the +2 oxidation state form complexes with octakis(benzylthio)tetraazaporphyrin [M{TAP(SBn)8}] (M=Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and 2H+; Bn=CH2Ph; TAP=tetraazaporphyrin) and were prepared via demetallation of the template-synthesized complex [Mg{TAP(SBn)8}] in ClCH2COOH, followed by insertion of the metal ions in a PhCl–DMF mixture. All compounds were characterized by u.v–vis, 1H-n.m.r., e.s.r. and mass spectra, microanalyses and magnetic susceptibility data. PM3 geometry optimization showed near coplanar arrangement of five phenyl rings vis-a-vis the TAP ring plane, while the remaining three phenyl rings lie bent over it. The Mn2+, Co2+ and Cu2+ complexes exhibited reversible one electron oxidation waves, that were observed at E1/2 -0.33, -0.29 and 0.58 V versus Ag/AgCl respectively. They all exhibited an irreversible reduction wave at Ep -1.1 V versusAg/AgCl followed by appearance of an irreversible oxidation wave at Ep 1.1–1.2 V versus Ag/AgCl. This has been interpreted in terms of reductive dissociation, leading to removal of the benzyl substituents, and subsequent oxidation of thiolate products. The Mn2+, Co2+ and Cu2+complexes exhibited metal ion-based e.s.r. signals. The [Co{TAP(SBn)8}] complex in a homogeneous DMF solution was found to catalyze electro-reduction/oxidation of nitrite ions. In the presence of a 1/5 molar quantity of the complex [Co{TAP(SBn)8}], the nitrite reduction peak was observed to be shifted by 0.1 V towards the positive potential side and the peak current rose by a factor of 1.33. Similarly a sharp rise in the anodic current, corresponding to oxidation of nitrite ions, was observed in the presence of the complex.

Enhanced electrochemical and electrocatalytic activity of a new supramolecular manganese-porphyrin species containing four bis(bipyridine)(aqua)ruthenium(II) complexes

A novel supramolecular species [MnTPyP{Ru(bipy) 2H 2O} 4](PF 6) 9 containing four cis-bis(bipyridine)(aqua)ruthenium(II) complexes attached to the peripheral pyridyl groups of meso-tetra(4-pyridyl)porphyrin manganese(III) (MnTPyP) has been synthesized, and employed as the precursor of a rather promising multinuclear oxo-transfer catalyst. This complex forms molecular films by dip coating. Such films are soluble in water, but can be stabilized by exchanging the PF − 6 anions by [Fe(CN) 6] 4− or [Zn–TPPS] 4−. They exhibit remarkable electrochemical and electrocatalytic activity, as demonstrated in the oxidation of nitrite ions. In this case, experimental evidence supports the involvement of electrochemically generated [ORu IV] 2+ groups in the oxidation reaction, reflecting the characteristic reactivity of high-valence metal–oxo complexes.