Ferrocyanide System Research Articles

Combining Optical and Raman Spectroscopy with Electrochemistry: The Ferricyanide and Ferrocyanide System - Experiments for Undergraduates

Combining Optical and Raman Spectroscopy with Electrochemistry: The Ferricyanide and Ferrocyanide System - Experiments for Undergraduates

Electrochemical properties of Au Nanoparticles

TiO2 NPs powder (titanium oxide nanoparticles powder) is synthesized via anodization in 0.7 M HClO4 is annealed in N2 at 450°C for 3 hrs to obtain the TiO2 NPs -N2 powder as catalyst support to which Au is loaded via photodeposition technique using tetrachloroauric acid (HAuCl4) and isopropanol as a sacrificial donor. The physicochemical characterizations of TiO2 NPs arrays powder were performed by transmission electron microscopy (TEM). The TEM image suggested that Au nanoparticles were circular and there was a tendency of agglomerations. The electro-catalytic activity of Au NPs/TiO2-NTs-N2 catalysts in ferrocyanide system , KOH ,and H2SO4 electro-oxidation was examined by cyclic voltammetry (CV) and contrasted with a financially accessible polycrystalline gold electrode. Au-TiO2 NPs-N2 powder electrode catalyst displays a strikingly high electrocatalytic activity in KOH and H2SO4 solutions. The results indicate Au NPs/TiO2-NTs-N2 catalysts as a promising support material improve the excellent electro-catalytic activity for acidic and basic oxidation.

Effect of distance between impeller blade tip and surface on mass transfer to a local electrode in a stirred vessel in a wide range of Sc number

ABSTRACT Stirred vessels are encountered in a wide scale of applications from bench to industrial processes, and the knowledge of the heat/mass transfer rates in these vessels is required for their design, operation and control. This work submits an investigation on the mass transfer to a small circular surface immersed in a stirred vessel in the parameter ranges of 267 < Re < 9437, 1473 < Sc < 61,422, and 0.022 < x/dK < 0.22 for the distance between the impeller blade tip and the transfer surface. The Reynolds number was based on the impeller diameter. The electrochemical limiting diffusion current technique having a potassium ferri-/ferrocyanide system was applied for mass transfer coefficient measurements. Aqueous glycerine solutions were prepared to attain a wide range of Sc numbers. The rate of mass transfer is enhanced with increasing rotation rate, decreasing blade tip-to-electrode surface distance, and decreasing glycerine concentration. The experimental data were well correlated by the relation .

Microbial water quality: Voltammetric detection of coliforms based on riboflavin–ferrocyanide redox couples

The ability to screen water for the presence of faecal contamination is a pressing need for rural communities dependent upon local purification systems. While there are a multitude of coliform detection assays based on the activity of β-galactosidase, this report details the adaptation of a voltammetric pH sensing strategy which could offer rapid analysis. The approach exploits the bacterial metabolism of lactose via pyruvate to lactate with the subsequent decrease in pH measured by examining the peak separation of a riboflavin (sensing) – ferrocyanide (reference) couple. Disposable carbon fibre electrodes were used as in situ sensors in Escherichia coli cultures (103–107 cfu/mL) with detection times of 4 h enabling confirmation of coliform activity. The bacterial compatibility of the riboflavin–ferrocyanide system in combination with the simplicity of the detection methodology, stand in marked contrast to many existing coliform assays and could open new avenues through which voltammetric pH sensing could be employed.

Electrochemical Charge Transfer Through the Supramolecular Discogen‐DNA Hybrid Multi‐layered Assembly

AbstractIn the present work, charge transfer phenomenon through the films of an ionic discotic liquid crystal (discogen) that is pyridinium tethered with hexaalkoxytriphenylene (PyTp) and its complex with DNA (PyTp‐DNA) was studied by using electrochemical methods. The PyTp and PyTp‐DNA hybrid films were first formed at the air‐water interface and then transferred onto the gold substrates by Langmuir‐Blodgett (LB) technique. Electrochemical measurements carried out on these films in three different redox systems, namely, ferrocene, hexaammineruthenium (III), and ferrocyanide, revealed that the ferrocene and the hexaammineruthenium (III) systems allow the electron transfer reaction between redox probes and metal, whereas the ferrocyanide system completely blocks it. The electrochemical response of the films, in the former two systems, has been attributed to the bridge mediated electron transfer process, whereas, in the ferrocyanide system, the impermeability of redox ions through these LB films is responsible for the complete blocking of electron transfer. Based on the observed results, this work highlights the possibility of novel charge transfer properties of discogen‐DNA type hybrid films for applications in molecular electronics.

Kinetic and Diffusion-Driven Instabilities in the Bromate–Sulfite–Ferrocyanide System

The spatiotemporal dynamics of the bromate-sulfite-ferrocyanide (BSF) reaction-diffusion system in a open one-side-fed reactor (OSFR) is investigated by numerical simulations. The results of the simulations are compared with experiments performed in an annular shape OSFR. Both kinetic and diffusion-driven instabilities are identified in the model. There are two hydrogen ion consuming pathways in the mechanism: the partial oxidation of sulfite to dithionate and the oxidation of ferrocyanide by bromate ions. Their dynamical effects are similar, as they support the same negative feedback loop via sulfite ion. However, the time scale of the oxidation of ferrocyanide by bromate ions can be conveniently controlled by the input feed concentrations, thus it provides a more flexible way to find spatiotemporal oscillations. Long-range activation due to the relative fast diffusion of hydrogen ions compared to the other reactants can also result in oscillations in this mechanism. We show that the spatial extent of the reaction-diffusion medium along the direction of the diffusive feed (the thickness) acts as a general control parameter of the dynamics. Oscillations, either originated in kinetic or in diffusive instabilities, can only develop in a narrow range of the thickness. This property explains the experimentally often observed spatial localization of the oscillations. A reciprocal relationship is found between two main control parameters of the dynamics, which are the thickness and the hydrogen ion input feed concentration.

On pH and Ca2+ Oscillations Monitored by pH Electrode and Ca‐ISE in Bromate–Sulfite–Ferrocyanide System Introduced Ca‐EDTA

The pH and Ca2+ oscillations of KBrO3–Na2SO3–K4Fe(CN)6 (BSF) system in presence of EDTA or Ca‐EDTA were investigated. Both EDTA and Ca‐EDTA can depress the amplitude and period of pH oscillation, and the effects of Ca‐EDTA are more obvious. These effects are attributed to the buffer effect in pH change. The Ca2+ oscillation appears as Ca‐EDTA introduced into the BSF system, which is ascribed to the stability of Ca‐EDTA being pH‐dependent. The pH and pCa (pCa = −log[Ca2+]) oscillations are synchronous in case of higher concentration of Ca‐EDTA; however, the chaotic behavior emerged in pCa oscillation arises at lower pH as the concentration of Ca‐EDTA is lower. Such observations can be understood by taking into account the interference of H+ on the response of Ca‐ISE to Ca2+. Both amplitude and period for pH and pCa oscillations as KCl introduced into the system can be obviously shortened due to the effect of ion strength on the reaction rate of the core oscillator and on the conditional formation constant of Ca‐EDTA. The results are significant for determining whether an experimentally observed chaos in chemical systems is of deterministic origin or is due to experimental noise.

Synthesis of highly dispersed platinum nanoparticles on multiwalled carbon nanotubes and their electrocatalytic activity toward hydrogen peroxide

Multiwalled carbon nanotubes were successfully coated with Pt nanoparticles through NH 3 gas pretreatment. Pt with particle size distribution of 1–4 nm was highly dispersed on carbon nanotubes. Cyclic voltammetry of ferrocyanide system was used to characterize the real electroactive surface area of platinum nanoparticle–multiwalled carbon nanotube (PtNP–MWCNT) coated glassy carbon electrode, and cyclic voltammetry for the PtNP–MWCNT coated electrode toward detecting H 2O 2 was measured to characterize the electrocatalytic property of the composite. Our results showed that the electroactive surface area of PtNP–MWCNT was higher than those of pristine multiwalled carbon nanotubes and Pt nanoparticles, and the composite exhibited the best electrocatalytic property for H 2O 2.

Radiolysis of ferrocyanide solutions studied by infrared spectroscopy

The behavior of the neutral and basic aqueous ferrocyanide system under irradiation is investigated using the coupling of a LINAC with infrared spectroscopy. The comparison between the neutral and basic system evidences the formation of the hydroxopentacyanoferrate (III) ions and gives information on the reaction mechanisms. The pseudo-protective effect of the dissolved dioxygen on the ferrocyanide is explained via a mechanism implying the superoxide radical anion.

First coupling between a LINAC and FT-IR spectroscopy: The aqueous ferrocyanide system

New results on the aqueous ferrocyanide system at neutral pH are presented here using the coupling of a 10 MeV LINAC with infrared spectroscopy. Seconds after irradiation, we observe a decrease of the Fe ( CN ) 6 4 - ferrocyanide ion concentration. Hydroxopentacyanoferrate(III) as well as hexacyanoferrate(III) ions are formed. After a 1500 Gy irradiation, we observe de-aquation of the former species, leading to the latter with a characteristic time of about 410 s and reduction of ferricyanide into ferrocyanide ions with a rate constant of 3 mol −1 dm 3 s −1. Berlin green is also detected when the irradiation dose is greater than 2500 Gy.

Morphological and electrochemical studies of spherical boron doped diamond electrodes

Morphological and electrochemical characteristics of boron doped diamond electrode in new geometric shape are presented. The main purpose of this study is a comparison among voltammetric behavior of planar glassy carbon electrode (GCE), planar boron doped diamond electrode (PDDE) and spherical boron doped diamond electrode (SDDE), obtained from similar experimental parameters. SDDE was obtained by the growth of boron doped film on textured molybdenum tip. This electrode does not present microelectrode characteristics. However, its voltammetric peak current, determined at low scan rates, is largest associated to the smallest Δ E p values for ferrocyanide system when compared with PDDE or GCE. In addition, the capacitance is about 200 times smaller than that for GCE. These results show that the analytical performance of boron doped diamond electrodes can be implemented just by the change of sensor geometry, from plane to spherical shape.

Electrochemical Mass Transfer Measurements with Glycerin Used To Reach High Schmidt Numbers

The electrochemical technique with the ferri−ferrocyanide system has been used to study mass transfer at high Schmidt numbers in a straight pipe and a Y-bifurcation flow model, with the latter being relevant to arterial blood flow and atherosclerosis. Results at higher Sc values were wanted in order to match blood properties (Sc ranging from 1.5 × 105 to 6 × 105). Glycerin was found to be the best viscosity modifier, although it posed some experimental problems; the presence of glycerin and sodium hydroxide results in the degradation of ferricyanide ions. The rate of degradation is directly proportional to the temperature and ferricyanide concentration. Thus, the experiments had to be performed rapidly after preparation of the solution. After optimization of the experimental conditions, a Schmidt number of about 50 000 was obtained, higher than those attained previously and likely the highest Schmidt number achieved experimentally in homogeneous solutions. Averaged mass transfer in both the pipe and the bifurcation showed the same trend as those obtained previously at lower Schmidt numbers. The dependence of the Sherwood number on Sc1/3 holds well for laminar flow up to at least Sc = 50 000. The 1/3 exponent also holds in turbulent flow, measured up to a Reynolds number of 10 000.

Structural and voltammetric studies at boron-doped diamond electrode grown on carbon felt produced from different temperatures

Diamond formation was studied on carbon felts (CF) substrates produced from an organic polymer, polyacrylonitrile (PAN), at different heat treatment temperatures (HTT). Knowledge and control of CF structural properties have demonstrated to be very important for growing boron-doped diamond (BDD) films on such substrates. During the deposition, fiber etching and diamond nucleation occur simultaneously and compete kinetically. In addition, these processes may also be affected by the HTT of the carbon fiber precursor. BDD/CF electrodes were produced by Hot Filament Chemical Vapor Deposition (HFCVD) and characterized by Scanning Electron Microscopy (SEM), Raman spectroscopy, X-Ray Diffraction (XRD) and Cyclic Voltammetry (CV) techniques. It also discussed the HTT influence on substrate structural properties correlated with diamond film growth and its electrochemical response. CF substrates were carburized in the temperatures of 1300, 1800 and 2300 K and presented respective increases in their conductivity values. CV measurements in ferri–ferrocyanide system have confirmed the superior properties of BDD/CF electrodes and showed evidence of a large surface area increase, which makes them appropriate to be used as porous electrode in different electrochemical applications.

Electrocatalytic oxidations of biological molecules (ascorbic acid and uric acids) at highly oxidized electrodes

Highly oxidized glassy carbon and other metal (gold and platinum) electrode surfaces were generated by applying 2.0 V vs. SCE for 600 s in pH 7 solution. The effects of oxidation on the functional, physical, and chemical characteristics of the electrodes went beyond the usual conditioning of such electrode surfaces through cycling to slightly beyond the medium decomposition potentials. The oxidized electrodes showed enhanced electrochemical activities and lower background currents. Besides cleaning the surface of contaminants introduced in the polishing stage of electrode preparation, application of such high potentials for an extended time interval changed the chemical nature of the glassy carbon surface itself. The chemical changes influenced the electro-oxidation reaction of bio-molecules such as ascorbic acid and uric acid but did not influence the reaction of the ferri- and ferrocyanide system. As a result the biological molecules (uric acid and ascorbic acid) were detected using an electrochemical method individually and simultaneously without the necessity for any electron relay complex.

Reductive transformations of halophenols on illuminated ferrocyanide ions

The reductive decomposition of several halogenated pollutants (2,4,5-trichlorophenol, 2,5 and 3,4-dichlorophenol, 2-and 4-chlorophenol, 4-bromophenol and 4-fluorophenol) was evaluated by adopting illuminated ferrocyanide ions as source for hydrated electrons; in these conditions, the photogenerated solvated electrons interact with substances present in solution so reducing them. The constant rates of halophenols with hydrated electrons achieved with ferrocyanide system show a good correlation with the data estimated by adopting pulse radiolysis, so that it could be adopted as an alternative to the pulse radiolysis in evaluating the reactivity of organic compounds toward hydrated electrons. Furthermore, it permits to pursue the fate of initial molecule through the intermediates identification. As an example, a detailed study about the intermediates produced from 3,4-dichlorophenol and 2,4,5-trichlorophenol is presented and a pattern of reaction pathways accounting for the recognized intermediates is proposed.

Reactivity of chloromethanes with photogenerated hydrated electrons

Ferrocyanide ion illuminated with proper light has shown to generate hydrated electrons. The photogenerated solvated electron may interact with substances present in solution reducing organic compounds present in aqueous solution. We have investigated the reductive degradation of chloromethanes (tetrachloromethane, chloroform and dichloromethane) adopting ferrocyanide system under anaerobic conditions and the obtained results have been compared with those obtained with the pulse radiolysis; a good correlation between the rate of disappearance evaluated with the two techniques is achieved.

Electrochemical Reaction in a High Gravity Field Vertical to an Electrode Surface-Analysis of Diffusion Process with a Gravity Electrode

With a new type of electrode system that utilizes the radial component of the centrifugal force instead of the real gravity force, the effect of the promoted gravity field on the diffusion process of ions was examined. First, the diffusion equation was derived in the case when the gravity field is imposed vertically onto an electrode surface. Then, it was theoretically clarified that numerous minute convection cells with sizes of the order of the diffusion layer thickness appear through a self-organization process from a top-heavy distribution of fluid density arising from the electrode reactions. The equation predicted that the diffusion current density is proportional to the 1/3rd order of the gravity acceleration and the 1st order of the difference between the bulk and surface concentrations. Then, we attempted to confirm this prediction by using the redox reaction of a ferricyanide–ferrocyanide system, and found that all of the experimental results exhibits good agreement with the predictions. Finally, the dependences of the diffusion coefficients of ferrocyanide and ferricyanide ions on the enhanced gravity fields were measured. However, for the gravity fields up to 650g, it was concluded that no remarkable dependence of the diffusion coefficient on the gravity is observed.

The electrochemical reactivity of amorphous hydrogenated carbon nitrides for varying nitrogen contents: the role of the substrate

A series of hydrogenated carbon nitride films have been deposited on titanium and n-type highly doped (1 0 0) silicon substrates by the integrated distributed electron cyclotron resonance reactor from acetylene and nitrogen gas mixtures. It has been found that for nitrogen content between 5 and 25% the electrical conductivity and the electrochemical reactivity, for an outer sphere reaction such as that due to the ferri–ferrocyanide system, varies in opposite directions. In addition the overall kinetic behaviour of the same system, looking similar to that of a simple electron transfer with a partial mass transfer in solution, contains another contribution. This can be explained by the presence of a more resistive layer within the carbon film and close to the solution, where electronic transport would occur by hopping between a large number of localised states. Finally, in contrast to the silicon substrate which introduces a resistive layer resulting in an additional potential drop, titanium seems to be a more promising substrate because of the negligibility of the latter effect.

Evaluation of hexose monophosphate shunt activity in isolated murine lens by monitoring the potential of the ferricyanide--ferrocyanide system.

A method for evaluation of the activity of the hexose monophosphate shunt (HMS) in isolated lens is presented. The measurement of HMS activity is based on continuous monitoring of the potential of the ferricyanide--ferrocyanide system (where ferricyanide is an artificial electron acceptor) in the presence of a lens. The rate of reduction of ferricyanide increased after the addition of methylene blue (MB) or saponin. The ferricyanide reduction rate did not correlate with GSH content in the contralateral lenses of the same mouse in the absence of MB or saponin. Correlations between the ferricyanide reduction rate and GSH content in the lens were 0.67 (beta = 0.93) in the presence of MB and 0.82 (beta = 0.95) in the presence of saponin. We think that the measured curves of ferricyanide reduction are representative of: 1) normal level of HMS activity (in the absence of methylene blue and saponin); 2) maximal HMS activity (in the presence of methylene blue); 3) the intracellular concentration of reducing equivalents (in the presence of saponin).

A subpicosecond, subnanosecond and steady-state study of diffusion-influenced fluorescence quenching

Subpicosecond and subnanosecond time resolved experiments are combined with steady-state fluorescence measurements to examine the diffusion influenced fluorescence quenching reaction of rhodamine B and ferrocyanide. The classic models of Smoluchowski, and Collins and Kimball are unable to consistently explain both the rapid initial decay and the slower decay seen at long times (&amp;gt;1 ns) in the experimental data. Neither the short nor the long time data can be reconciled with the steady-state data using these models. Better agreement is found between the data and a simple model incorporating a position dependent intrinsic reaction rate [A. Szabo, J. Chem. Phys. 93, 6929 (1989)] in addition to a diffusional rate. This model suggests a rate of electron transfer for the rhodamine B–ferrocyanide system of (27.5±4 ps)−1. Use of a bare Coulomb potential between reactants is found to be inappropriate in all of the models investigated.