Search

Hydrazine and nitrite are well known as carcinogenic substances, which however, are commonly used in chemical industry and food processing. Monitoring of such two species in water and food is necessary. Here, we report a convenient electroanalytical method for detection of hydrazine and nitrite by facile preparation of graphene–cobalt hexacyanoferrate nanocomposite through a two-step electrode surface functionalization. The morphology and constituent of the prepared nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Cyclic voltammetry was used to profile the electrochemical behaviors of hydrazine and nitrite, revealing the synergetic electrocatalytic function of reduced graphene oxide and cobalt hexacyanoferrate nanoparticles. This was confirmed by the decreased oxidation overpotentials and increased current response of the target analytes, and thus offered a premise for electroanalysis. The quantitative measurements were carried out by amperometry and differential pulse voltammetry, respectively. Moreover, the analytical utility was demonstrated by determination of water samples and pickled food; the average recovery was found to be from 92.2% to 108%, with the relative standard deviation (RSD) less than 7.8%. The present method opens an avenue for detection of potential carcinogens in relation to environment and food territory. [ABSTRACT FROM AUTHOR]

Highlights: [•] Iron oxyhydroxide@cobalt hexacyanoferrate coaxial nanostructure was synthesized. [•] The nanostructure showed an excellent pseudocapacitive behavior. [•] The electrode is biocompatible. [ABSTRACT FROM AUTHOR]

Highlights: [•] Redox state of cobalt hexacyanoferrate layer at electrode can be estimated by Raman spectroscopy. [•] Redox processes within this layer are limited by intrinsic electron transfer rate. [•] Electroreduction of hydrogen peroxide is limited by slow redox transformations within the modifier layer. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a cobalt hexacyanoferrate/large-mesopore carbon modified glassy carbon electrode (CoHCF–LMC/GC) was simply fabricated by electrodepositing CoHCF film on LMC. The electrochemical behaviors of L-dopa at this modified electrode have been studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and amperometry. The results show that the CoHCF–LMC modified electrode exhibits efficiently electrochemical activity for L-dopa oxidation in 0.1M PBS (pH=7.4), and the quantitative determination of L-dopa is unperturbed by the ascorbic acid (AA). Amperometry results depict that the proposed sensor provides excellent performance towards the determination of L-dopa with a low detection limit of 1.7×10−8 M in the wide concentration range from 1.0×10−7 to 1.9×10−3 M at +0.20V versus Ag/AgCl. Moreover, the studied composite electrode exhibits a good reproducibility and long-term stability. Determination of L-dopa in commercial tablets and human blood serum with satisfying results was also investigated by the proposed composite electrode. [Copyright &y& Elsevier]

Abstract: In this work, cobalt hexacyanoferrate (CoHCF) modified screen-printed electrodes were developed and characterised electrochemically. The effect of different cations was investigated showing a more reversible system with a well-defined peak around +0.35V vs. Ag/AgCl when Na+ was used as cation in the supporting electrolyte. The transfer coefficient (α) and the apparent charge transfer rate constant (k s) for electron transfer between the electrode and the CoHCF layer was calculated. The electrocatalytic behaviour of CoHCF towards oxidation of enzymatically generated thiocholine was thoroughly investigated. Cyclic voltammetry experiments performed in thiocholine solution showed the classical shape of a mediated redox system. The diffusion constant of thiocholine was estimated using chronoamperometry. Also, the catalytic rate constant k of thiocholine at CoHCF–SPE was determined. The current due to thiocholine mediated oxidation was then evaluated in batch amperometric mode at +0.5V vs. Ag/AgCl obtaining a linear range (5×10−7–1×10−5 molL−1) with a low detection limit and a high sensitivity equal to 5×10−7 molL−1 and 435mAmol−1 Lcm−2, respectively. [Copyright &y& Elsevier]

Abstract: Cobalt hexacyanoferrate (CoHCF) nanotubes with high aspect ratio were fabricated by sequential deposition method using the porous anodic aluminum oxide (AAO) template, which was prepared by two-step anodization method. The nanotubes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and ultraviolet/visible (UV–vis) spectroscopy. The results of XRD and X-rays energy dispersive analysis indicated that the nanotubes had a cubic structure with cell constant of a =10.24Ǻ and atomic ratio of Co to Fe of 3:2. The formation mechanism of CoHCF nanotubes in the inner wall of AAO template was discussed and verified by the cross-sectional SEM images. The electrochemical characteristics of CoHCF nanotubes were investigated by cyclic voltammetry and its cyclic voltammogram was characterized with two couples of redox peaks with the formal potential of 652 and 467mV, respectively, in 0.2M of KCl solution at a scan rate of 20mV/s. The voltammetric results also indicated that the CoHCF nanotubes had high electrocatalytic activities toward the oxidation of ascorbic acid and dopamine compared with that of bulk prepared CoHCF sample. The methods presented in this work can be extended to fabricate nanotubes of hexacyanoferrates of other transition or rare earth metals. [Copyright &y& Elsevier]

Abstract: Electrochemical impedance spectroscopy (EIS) was used in conjunction with cyclic voltammetry and UV–vis spectroelectrochemistry to study the influence of growth history on compounds formed in the cobalt hexacyanoferrate (CoHCF) family and their redox inter-relationships. The CoHCF films were potentiodynamically grown via precipitation on polycrystalline gold substrates from a 1M KNO3 medium dosed with Co2+ and precursor species. The growth variables were the precursor concentration ratio: , potential window for film growth, delay time (between precursor mixing and potential cycling), and the number of potentiodynamic cycles for film growth. The combined use of the data from the three techniques identified above has afforded identification of the various CoHCF compounds that constitute the films and their redox inter-relationships. [Copyright &y& Elsevier]

An electroactive cobalt hexacyanoferrate (CoHCF) film was electrodeposited from a solution containing Co2+ and Fe(CN)63- ions on the bare gold or the Au-colloid modified electrode. The cation (Li+, Na+, K+, Rb+, Cs+, Mg2+, Ca2+, Sr2+ and Ba2+) and the anion (F-, Cl- and Br-) effects on the redox peak of the CoHCF film were investigated in detail. On the other hand, the electrocatalytic oxidations of thiosulfate at the CoHCF/gold and CoHCF/Au-colloid/gold electrodes were compared. At the CoHCF/Au-colloid/gold electrode, we obtained a response current larger by a factor of 2 and a three times lower detection limit than those at a CoHCF/gold electrode. The linear ranges were 1.0 × 10-4 to 2.8 × 10-3 M for the CoHCF/gold electrode and 7.5 × 10-5 to 4.8 × 10-3 M for the CoHCF/Au-colloid/gold electrode. These results showed that the immobilized CoHCF at the Au-colloid modified electrode exhibited a higher catalytic activity and a wider linear range toward thiosulfate. Additionally, the effects of the applied potential and the solution pH were studied. [Copyright &y& Elsevier]