Electrocatalytic oxidation and detection of hydrazine at carbon nanotube-supported palladium nanoparticles in strong acidic solution conditions

Pd nanoparticle catalysts supported by multiwall carbon nanotubes (Pd/MWNTs) prepared using a complexation–reduction method are used in this study for the electrochemical determination of hydrazine. The physico-chemical properties of the Pd/MWNT catalyst were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and scanning electron microscopy physico-chemical (SEM). These structural analyses reveal that the Pd/MWNTs-modified glassy carbon electrode possesses a three-dimensional network structure in which the Pd nanoparticles, with an average size of 5 nm, are uniformly distributed on the surface of the MWNTs. After Nafion solution was coated on the surface of the Pd/MWNT layer, the resulting Pd/MWNT–Nafion modified electrode retained the three-dimensional network structure. Electrochemical measurements show that the oxidation peak current of hydrazine decreases with increasing pH. Under optimum conditions, the Pd/MWNT–Nafion-based hydrazine sensor exhibits a broad linear calibration range (2.5–700 μM) and a low detection limit of 1.0 μM for hydrazine.     

Renewable-surface sol-gel derived carbon ceramic-modified electrode fabricated by a newly synthesized polypyridil and phosphine Ru (II) complex and its application as an amperometric sensor for hydrazine

A chemically modified carbon ceramic composite electrode (CCE) containing Dichloro{(8, 9-dimethyl-dipyridio [2,3-a;2′,3′-c] phenazine-κ²-N,N′) bis(triphenylphosphine-κ-P)}ruthenium (II) complex which synthesized newly was constructed by the sol-gel technique. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltammetry. The electrocatalytic activity of CCE was investigated and showed a good effect for oxidation of hydrazine in phosphate buffer solution (PBS). A linear concentration range of 6 μM to 1.2 mM of hydrazine with an experimental detection limit of 1 μM of hydrazine was obtained. The diffusion coefficient of hydrazine and its catalytic rate constant for electrocatalytic reaction along with the apparent electron transfer rate constant (k_s) and transfer coefficient (α) were also determined.The modified carbon ceramic electrode doped with this new Ru-complex showed good reproducibility, short response time (t < 2 s), remarkable long-term stability (>3 month) and especially good surface renewability by simple mechanical polishing.The results showed that this electrode could be used as an electrochemical sensor for determination of hydrazine in real water samples used in Fars Power Plant Station, including its heat recovery steam generator (HRSG) water (at different operational condition), cooling system and clean waste water.     

Copper (hydr)oxide modified copper electrode for electrocatalytic oxidation of hydrazine in alkaline media

Stable copper (hydr)oxide modified copper electrode was prepared by cyclic voltammetry in 0.1 M NaOH solution in the potential range of −300 to 800 mV. In the first cycle the oxidation peaks of copper were observed but in the second and next cycles, they were omitted and a clean background was obtained. This indicates that an irreversible electrochemical transformation has been achieved during the first cycle and a stable layer of hydr(oxide) formed on the surface of the copper electrode. This layer protects the electrode from corrosion. This electrode can be used for electrochemical studies in the potential range of −300 to 800 mV without any interfering effects by the oxidation peaks of copper. The modified electrode was used for electrocatalytic oxidation of hydrazine. Results showed that on the bare copper electrode the oxidation peak of 10 mM hydrazine appear at 380 mV while on the copper (hydr)oxide modified copper electrode, it appear at 260 mV. About 120 mV negative shift of the peak potential indicated the catalytic activity of (hydr)oxide layer for hydrazine. The kinetic parameters were investigated by using cyclic voltammetry and chronoamperometry.     

Voltammetric determination of bisoprolol fumarate in pharmaceutical formulations and urine using single-wall carbon nanotubes modified glassy carbon electrode

The electrochemistry of bisoprolol fumarate (BF) has been investigated by differential pulse voltammetry at a single-wall carbon nanotubes (SWNTs) modified glassy carbon electrode (GCE). The prepared electrode showed an excellent electrocatalytic activity towards the oxidation of BF leading to a marked improvement in sensitivity as compared to bare glassy carbon electrode where electrochemical activity for the analyte cannot be observed. The SWNTs-modified GCE exhibited a sharp anodic peak at a potential of ∼950 mV for the oxidation of BF. Under optimum conditions linear calibration curve was obtained over the BF concentration range 0.01-0.1 mM in 0.5 M phosphate buffer solution (pH 7.2) with a correlation coefficient of 0.9789 and detection limit of 8.27 × 10⁻⁷ M. The modified electrode has been applied for the drug determination in human urine with no prior extraction and in commercial tablets. The proposed method has also been validated.     

Highly sensitive and simultaneous determination of hydroquinone and catechol at poly(thionine) modified glassy carbon electrode

A simple and highly sensitive electrochemical method for the simultaneous and quantitative detection of hydroquinone (HQ) and catechol (CT) was developed, based on a poly(thionine)-modified glassy carbon electrode (GCE). The modified electrode showed excellent electrocatalytic activity and reversibility towards the oxidation of both HQ and CT in 0.1 M phosphate buffer solution (PBS, pH 7.0). The peak-to-peak separations (ΔE_p) between oxidation and reduction waves in CV were decreased significantly from 262 and 204 mV at the bare GCE, to 63 and 56 mV, respectively for HQ and CT at the poly(thionine) modified GCE. Furthermore, the redox responses from the mixture of HQ and CT were easily resolved in both CV and DPV due to a difference in the catalytic activity of the modified GCE to each component. The peak potential separation of ca. 0.1 V was large enough for the simultaneous determination of HQ and CT electrochemically. The oxidation peak currents of HQ and CT were linear over the range from 1 to 120 μM in the presence of 100 and 200 μM of HQ and CT, respectively. The modified electrode showed very high sensitivity of 1.8 and 1.2 μA μM⁻¹ cm⁻² for HQ and CT, respectively. The detection limits (S/N = 3) for HQ and CT were 30 and 25 nM, respectively. The developed sensor was successfully examined for real sample analysis with tap water and revealed stable and reliable recovery data.     

Hematoxylin multi-wall carbon nanotubes modified glassy carbon electrode for electrocatalytic oxidation of hydrazine

A new hydrazine sensor has been fabricated by immobilizing hematoxylin at the surface of a glassy carbon electrode (GCE) modified with multi-wall carbon nanotube (MWCNT). The adsorbed thin films of hematoxylin on the MWCNT modified GCE show one pair of peaks with surface confined characteristics. The hematoxylin MWCNT (HMWCNT) modified GCE shows highly catalytic activity toward hydrazine electro-oxidation. The results show that the peak potential of hydrazine at HMWCNT modified GCE surface shifted by about 167 and 255 mV toward negative values compared with that at an MWCNT and activated modified GCE surface, respectively. In addition, at HMWCNT modified electrode surface remarkably improvement the sensitivity of determination of hydrazine. The kinetic parameters, such as the electron transfer coefficient, α, and the standard heterogeneous rate constant, k⁰, for oxidation of hydrazine at the HMWCNT modified GCE were determined and also is shown that the heterogeneous rate constant, k′, is strongly potential dependent. The overall number of electron involved in the catalytic oxidation of hydrazine and the number of electrons involved in the rate-determining steps are 2 and 1, respectively. The amperometric detection of hydrazine is carried out at 220 mV in 0.1 M phosphate buffer solution (pH 7) with linear response range 2.0-122.8 μM hydrazine, detection limit of 0.68 μM and sensitivity of 0.0208 μA μM⁻¹. Finally the amperometric response for hydrazine determination is reproducible, fast and extremely stable, with no loss in sensitivity over a continual 400 s operation.     

Electrocatalytic and simultaneous determination of isoproterenol, uric acid and folic acid at molybdenum (VI) complex-carbon nanotube paste electrode

This paper describes the development, electrochemical characterization and utilization of a novel modified molybdenum (VI) complex-carbon nanotube paste electrode for the electrocatalytic determination of isoproterenol (IP). The electrochemical profile of the proposed modified electrode was analyzed by cyclic voltammetry (CV) that showed a shift of the oxidation peak potential of IP at 175 mV to less positive value, compared with an unmodified carbon paste electrode. Differential pulse voltammetry (DPV) in 0.1 M phosphate buffer solution (PBS) at pH 7.0 was performed to determine IP in the range from 0.7 to 600.0 μM, with a detection limit of 35.0 nM. Then the modified electrode was used to determine IP in an excess of uric acid (UA) and folic acid (FA) by DPV. Finally, this method was used for the determination of IP in some real samples.     

Electrochemical behavior and voltammetric determination of 4-aminophenol based on graphene-chitosan composite film modified glassy carbon electrode

The graphene-chitosan composite film modified glassy carbon electrode (GCE) was fabricated and used to determine 4-aminophenol (4-AP). In 0.1 M pH 6.3 phosphate buffer solution, the redox peak currents of 4-AP increased significantly and the peak-to-peak separation decreased greatly at graphene-chitosan composite film modified GCE compared with bare GCE and chitosan modified GCE, indicating that graphene possessed electrocatalytic activity towards 4-AP. The experimental conditions were optimized and the kinetic parameters were investigated. The oxidation mechanism was discussed. Under the optimal experimental conditions, the oxidation peak current was proportional to 4-AP concentration in the range from 0.2 to 550 μM with the correlation coefficient of 0.9930. The detection limit was 0.057 μM (S/N = 3). Using the proposed method, 4-AP was successfully determined in water samples and paracetamol tablets with standard addition method, suggesting that this method can be applied to determine 4-AP in environments and pharmaceuticals.     

Electrochemical characterization of poly(eriochrome black T) modified glassy carbon electrode and its application to simultaneous determination of dopamine, ascorbic acid and uric acid

A polymerized film of eriochrome black T (EBT) was prepared on the surface of a glassy carbon (GC) electrode in alkaline solution by cyclic voltammetry (CV). The redox response of the poly(EBT) film at the GC electrode appeared in a couple of redox peak in 0.1 M hydrochloride and the pH dependent peak potential was −55.1 mV/pH which was close to the Nernst behavior. The poly(EBT) film-coated GC electrode exhibited excellent electrocatalytic activity towards the oxidations of dopamine (DA), ascorbic acid (AA) and uric acid (UA) in 0.05 mM phosphate buffer solution (pH 4.0) and lowered the overpotential for oxidation of DA. The polymer film modified GC electrode conspicuously enhanced the redox currents of DA, AA and UA, and could sensitively and separately determine DA at its low concentration (0.1 μM) in the presence of 4000 and 700 times higher concentrations of AA and UA, respectively. The separations of anodic peak potentials of DA-AA and UA-DA reached 210 mV and 170 mV, respectively, by cyclic voltammetry. Using differential pulse voltammetry, the calibration curves for DA, AA and UA were obtained over the range of 0.1-200 μM, 0.15-1 mM and 10-130 μM, respectively. With good selectivity and sensitivity, the present method provides a simple method for selective detection of DA, AA and UA in biological samples.     

Deposition of new thia-containing Schiff-base iron (III) complexes onto carbon nanotube-modified glassy carbon electrodes as a biosensor for electrooxidation and determination of amino acids

Multiwall carbon nanotubes (MWCNTs) were used as an immobilization matrix to incorporate an Fe (III)–Schiff base complex as an electron-transfer mediator onto a glassy carbon electrode surface. First, the preheated glassy carbon was subjected to abrasive immobilization of MWCNTs by gently rubbing the electrode surface on filter paper supporting the carbon nanotubes. Second, the electrode surface was modified by casting 100 μL of an Fe (III)-complex solution (0.01 M in ACN). The cyclic voltammograms of the modified electrode in an aqueous solution displayed a pair of well-defined, stable and nearly reversible reductive oxidation redox systems with surface confined characteristics. Combinations of unique electronic and electrocatalytic properties of MWCNTs and Fe (III)–Schiff base complexes resulted in a remarkable synergistic augmentation of the response. The electrochemical behavior and stability of the modified electrode in aqueous solutions at pH 1–9 were characterized by cyclic voltammetry. The apparent electron transfer rate constant (K_s) and transfer coefficient (a) were determined by cyclic voltammetry and were approximately 7 s⁻¹ and 0.55, respectively. The modified electrodes showed excellent catalytic activity towards the oxidation of amino acids at an unusually positive potential in acidic solution. They also displayed inherent stability at a wide pH range, fast response time, high sensitivity, low detection limit and had a remarkably positive potential oxidation of amino acids that decreased the effect of interferences in analysis. The linear concentration range, limits of detection (LOD), limits of quantization (LOQ) and relative standard deviation of the proposed sensor for the amino acid detection were 1–55,000, 1.10–13.70, 2.79–27.14 and 1.30–5.11, respectively.     

Electrocatalytic oxidation of methanol on carbon paste electrode modified by nickel ions dispersed into poly (1,5-diaminonaphthalene) film

Poly (1,5-diaminonaphthalene) film was prepared by using the repeated potential cycling technique in an acidic solution at the surface of carbon paste electrode. Then transition metal ions of Ni(II) were incorporated to the polymer by immersion of the modified electrode in a 1.0 M nickel chloride solution. The electrochemical characterization of this modified electrode exhibits stable redox behavior of the Ni(III)/Ni(II) couple. Also, cyclic voltammetric experiments showed that methanol electrooxidized at the surface of this Ni(II) dispersed polymeric modified carbon paste electrode [Ni/P-1,5-DAN/MCPE]. The mechanism of methanol oxidation changes from diffusion control at low concentration to a catalytic reaction at higher methanol concentration. The effects of both scan rate and methanol concentration on the anodic peak height of the methanol oxidation were discussed.     

Poly(o-aminophenol) film prepared in the presence of sodium dodecyl sulfate: Application for nickel ion dispersion and the electrocatalytic oxidation of methanol and ethylene glycol

Poly(o-aminophenol) (POAP) was formed by successive cyclic voltammetry in monomer solution in the presence of sodium dodecyl sulfate (SDS) on the surface of a carbon paste electrode. The electrochemical behavior of the SDS-POAP carbon paste electrode has been investigated by cyclic voltammetry in 0.5 M HClO₄ and 5 mM K₄[Fe(CN)₆]/0.1 M KCl solutions as the supporting electrolyte and model system, respectively. Ni(II) ions were incorporated into the electrode by immersion of the polymeric modified electrode having amine groups in 0.1 M Ni(II) ion solution. Cyclic voltammetric and chronoamperometric experiments were used for the electrochemical study of this modified electrode. A good redox behavior of the Ni(III)/Ni(II) couple at the surface of electrode can be observed. The electrocatalytic oxidations of methanol and ethylene glycol (EG) at the surface of the Ni/SDS-POAP electrode were studied in a 0.1 M NaOH solution. Compared to bare carbon paste and POAP-modified carbon paste electrodes, the SDS-POAP electrode significantly enhanced the catalytic efficiency of Ni ions for methanol oxidation. Finally, using a chronoamperometric method, the catalytic rate constants (k) for methanol and ethylene glycol were found to be 2.04 × 10⁵ and 1.05 × 10⁷ cm³ mol⁻¹ s⁻¹, respectively.     

Electrochemical determination of bisphenol A at Mg-Al-CO3 layered double hydroxide modified glassy carbon electrode

The electrochemical behavior of bisphenol A (BPA) was investigated on Mg-Al layered double hydroxide (LDH) modified glassy carbon electrode (GCE) by cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and chronocoulometry (CC). The cyclic voltammogram of BPA on the modified electrode exhibited a well defined anodic peak at 0.454 V in 0.1 M pH 8.0 phosphate buffer solution (PBS). The experimental parameters were optimized and the kinetic parameters were investigated. The probable oxidation mechanism was proposed. Under the optimized conditions, the oxidation peak current was proportional to BPA concentration in the range from 1 × 10⁻⁸ to 1.05 × 10⁻⁶ M with the correlation coefficient of 0.9959. The detection limit was 5.0 × 10⁻⁹ M (S/N = 3). The fabricated electrode showed good reproducibility, stability and anti-interference. The proposed method was successfully applied to determine BPA in plastic products and the results were satisfactory.     

Nanomolar concentrations determination of hydrazine by a modified carbon paste electrode incorporating TiO2 nanoparticles

In the present paper, the use of a carbon paste electrode modified by quinizarine (QZ) and TiO(2) nanoparticles prepared by a simple and rapid method was described. The heterogeneous electron-transfer properties of quinizarine coupled to TiO(2) nanoparticles at a carbon paste electrode was investigated using cyclic voltammetry and chronoamperometry in aqueous buffer solutions. The modified electrode showed excellent character for the electrocatalytic oxidization of hydrazine (HZ). Differential pulse voltammetric peak currents of HZ increased linearly with their concentrations at the range of 0.5 μM to 1900.0 μM and the detection limit (2σ) was determined to be 77 nM. Finally, this method was used for the determination of HZ in water samples, using a standard addition method.     

Electrochemical reduction of nitrite at poly-[Ru(5-NO2-phen)2Cl] tetrapyridylporphyrin glassy carbon modified electrode

This work describes the preparation of modified electrodes with Poly-tetraruthenated porphyrin. Also, a detailed Raman and electrochemical characterization of these surfaces is shown. Glassy carbon electrodes were modified with Ni (II), Zn (II) and metal free polymeric film of tetrapyridylporphyrin coordinated to four [Ru(5-NO₂-phen)₂Cl]⁺ moieties.These modified electrodes are very stable in aqueous solutions, and were evaluated for the electrochemical reduction of nitrite ion at pH = 5.9 in 0.1 M NaClO₄. When the solution contains 0.01 M nitrite, linear sweep voltammetry results, show an enhancement in the current from −0,3 V with the conducting polymers, compared to the bare electrode behavior. Analyses after controlled potential electrolysis experiments verify the production of hydrazine, hydroxylamine and ammonia. Hydroxylamine was the product of higher production among the three studied catalysts.The behavior of the modified electrodes allows predicting that the reduction process of nitrite takes place through reduced macrocycle ring. The electrocatalytic activity of the modified electrodes, measured as turn over frequency is dependent on the potential and the central ion in the cavity of the macrocycle. Finally, the modified electrode containing Ni²⁺ in the cavity of the macrocycle was used as an amperometric sensor toward nitrite detection. The results show a limit of detection of 9.37 × 10⁻⁶ M and a linear rage of concentration of 1.49 × 10⁻⁵ to 1.24 × 10⁻⁴ M.     

Electrocatalytic hydrazine oxidation on quinizarine modified glassy carbon electrode

The electrocatalytic oxidation of hydrazine has been studied on glassy carbon modified by electrodeposition of quinizarine, using cyclic voltammetry and chronoamperometry techniques. It has been shown that the oxidation of hydrazine to nitrogen occurs at a potential where oxidation is not observed at the bare glassy carbon electrode. The apparent charge transfer rate constant and transfer coefficient for electron transfer between the electrode surface and immobilized quinizarine were calculated as 4.44 s⁻¹ and 0.66, respectively. The heterogenous rate constant for oxidation of hydrazine at the quinizarine modified electrode surface was also determined and found to be about 4.83 × 10³ M⁻¹ s⁻¹. The diffusion coefficient of hydrazine was also estimated as 1.1 × 10⁻⁶ cm² s⁻¹ for the experimental conditions, using chronoamperometry.     

A novel hydrazine electrochemical sensor based on a zirconium hexacyanoferrate film-bimetallic Au–Pt inorganic–organic hybrid nanocomposite onto glassy carbon-modified electrode

This work describes the electrochemical behavior of zirconium hexacyanoferrate (ZrHCF) film immobilized on the surface of bimetallic Au–Pt inorganic–organic hybrid nanocomposite glassy carbon electrode and its electrocatalytic activity toward the oxidation of hydrazine. The electrode possesses a three-dimensional (3D) porous network nano architecture (NFs). The surface structure and composition of the sensor was characterized by scanning electron microscopy (SEM). Electrocatalytic oxidation of hydrazine on the surface of modified electrode was investigated with cyclic voltammetry and chronoamperometry methods and the results showed that the ZrHCF film displays excellent electrochemical catalytic activities toward hydrazine oxidation. The modified electrode indicated reproducible behavior and high level of stability during the electrochemical experiments.     

Electrocatalytic oxidation of methanol and ethanol at carbon ceramic electrode modified with platinum nanoparticles

The use of carbon ceramic electrode (CCE) modified with platinum particles was studied for the electrocatalytic oxidation of methanol and ethanol by cyclic voltammetry and chronoamperometry. After preparation of a carbon ceramic as an electrode matrix by sol–gel technique, its surface was potentiostatically coated with Pt nanoparticles at −0.2 V vs. SCE in an aqueous solution of 0.1 M H₂SO₄ containing 0.002 M H₂PtCl₆. The electrocatalyst was characterized by XRD, SEM and cyclic voltammetry. The effective parameters on electrocatalytic oxidation of the alcohols, i.e. the amount Pt loadings, medium temperature and working potential limit in anodic direction were investigated and the results were discussed. This modified electrode showed an enhanced current density over the other Pt-modified electrodes making it more attractive for fuel cell applications.     

Electrochemical behaviors of thymine on a new ionic liquid modified carbon electrode and its detection

A new electrochemical method was proposed for the determination of thymine, which relied on the oxidation of thymine at a carbon ionic liquid electrode (CILE) in a pH 5.0 Britton-Robinson buffer solution. CILE was fabricated by using ionic liquid 1-(3-chloro-2-hydroxy-propyl)-3-methylimidazole acetate as the binder, which showed strong electrocatalytic ability to promote the oxidation of thymine. A single well-defined irreversible oxidation peak appeared with adsorption-controlled process and enhanced electrochemical response on the CILE, which was due to the presence of high conductive ionic liquid on the electrode. The reaction parameters of thymine were calculated with the electron transfer coefficient (α) as 0.27, the electron transfer number (n) as 1.23, the apparent heterogeneous electron transfer rate constant (k_s) as 6.87 × 10⁻⁶ s⁻¹ and the surface coverage (Г_T) as 5.71 × 10⁻⁸ mol cm⁻². Under the selected conditions the oxidation peak current was proportional to thymine concentration in the range from 3.0 to 3000.0 μM with the detection limit as 0.54 μM (3σ) by differential pulse voltammetry. The proposed method showed good selectivity to the thymine detection without the interferences of coexisting substances.     

Electrochemical sensors for hemoglobin and myoglobin detection based on methylene blue-multiwalled carbon nanotubes nanohybrid-modified glassy carbon electrode

An effective electrochemical sensors for hemoglobin (Hb) and myoglobin (Mb) detection was firstly developed using a simple procedure of self-assembled methylene blue-multiwalled carbon nanotubes (MB-MWNTs) nanohybrid modified on glassy carbon electrode without using any enzymes immobilization. The direct electrochemical and electrocatalytic behaviors of the modified electrode were studied using cyclic voltammetry (CV) and flow injection analysis (FIA) with amperometry. The performance of the sensor was investigated and optimized and the system was evaluated by monitoring Hb and Mb concentrations. The developed MB-MWNTs nanohybrid modified electrode showed excellent electrocatalytic activity for reduction of Hb and Mb with good stability, sensitivity and reproducibility (RSD = 3.05% and 4.5% for 50 successive injections of Hb and Mb, respectively). Under optimal conditions, the catalytic currents are linearly proportional to the concentrations of Hb and Mb in the wide range from 5 nM to 2 μM and 0.1 to 3 μM, and the corresponding detection limits are 1.5 nM and 20 nM (S/N = 3), respectively. This approach provides improved detection limit over other previous works and may provide a novel and efficient platform for the fabrication of sensors for other heme proteins.