Preparation,Characterization, and Electrocatalytic Properties of Mixed‐Valent Nickel Hexacyanoferrate/Phosphomolybdate Hybrid Film Electrodes Towards Oxidation of Ascorbic Acid and Reduction of S2O$\rm{ {_{8}^{2-}}}$

Polynuclear mixed‐valent nickelhexacyanoferrate/phosphomolybdate (NiHCF/PMo), nickel/phosphomolybdate (Ni/PMo) hybrid films were prepared on glassy carbon electrode by multiple scan cyclic voltammetry. Combination of individual components gave the opportunity to fabricate hybrid film with tunable electrochemical and analytical properties compared to individual components. The film growth was monitored using electrochemical quartz crystal microbalance (EQCM). The cyclic voltammogram of the nickelhexacyanoferrate/phosphomolybdate film is characterized by four redox couple whereas nickel/phosphomolybdate hybrid film exhibits three redox couples. Cyclic voltammetric features suggest that the charge transfer process in both films resembles that of surface‐confined redox species. The voltammetric response of nickelhexacyanoferrate/phosphomolybdate film electrode was found to be depending on the pH of the contacting solution. Electrocatalytic behavior of nickel/phosphomolybdate hybrid film coated electrodes toward oxidation of ascorbic acid and reduction of sulfur oxoanion, S₂O , was investigated using cyclic voltammetry technique. Analytical application of nickel/phosphomolybdate hybrid film electrode was tested in amperometry and flow injection analysis.     

Preparation,Characterization, and Bioelectrocatalytic Properties of Hemoglobin Incorporated Multiwalled Carbon Nanotubes‐Poly‐L‐lysine Composite Film Modified Electrodes Towards Bromate

The present work describes preparation of hemoglobin‐incorporated multiwalled carbon nanotubes‐poly‐L ‐lysine (MWCNT‐PLL)/Hb) composite modified electrode film modified glassy carbon electrode (GCE) and its electrocatalytic behavior towards reduction of bromate ( ) in 0.1 M acetate buffer (pH 5.6). The modified electrode has been successfully fabricated by immobilizing hemoglobin on MWCNT dispersed in poly‐L ‐lysine. The surface morphologies of MWCNT, PLL and Hb were characterized using atomic force microscopy (AFM). The voltammetric features suggested that the charge transport through the film was fast and the electrochemical behavior resembles that of surface‐confined redox species. Cyclic voltammetry was used to investigate the electrocatalytic behavior of the modified electrode towards bromate and was compared with that of the CNT‐modified as well as bare electrode. The analytical determination of bromate has been carried out in stirred solution at an optimized potential with a sensitivity of 7.56 μA mM^?1 and the calibration curve was linear between 1.5×0^?5 to 6.0×0^?3 M.     

Electrochemical Properties of Ordered Mesoporous Carbon Film Adsorbed onto a Self‐Assembled Alkanethiol Monolayer on Gold Electrode

A stable ordered mesoporous carbon (OMC) film electrode was successfully constructed by adsorbing OMC onto a self‐assembled monolayer (SAM) of C₁₈H₃₇SH chemisorbed on the Au electrode. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and electrochemical methods were used to characterize the properties of the OMC film electrode. The adsorbed OMC can restore the heterogeneous electron transfer almost totally blocked by the alkanethiol monolayer. Nyquist plots show a sharply decrease of the charge transfer resistance (R_ct) of the Fe(CN) couple at the OMC film electrode. Furthermore, the OMC film electrode is found to possess a significantly reduced interfacial capacitance and largely enhanced current response of hydrogen peroxide. This novel approach to the fabrication of stable OMC film electrode with excellent electrochemical properties is believed to be very attractive for electrochemical studies and electroanalytical applications.     

多壁碳纳米管-聚茜素红膜修饰电极测定多菌灵

制备了多壁碳纳米管-聚茜素红膜(MWNT-PAR)修饰电极,用循环伏安法和线性扫描伏安法、计时电量法等研究多菌灵在修饰电极上的电化学行为.结果表明,多菌灵在MWNT-PAR修饰电极上是扩散控制的不可逆电氧化过程.实验测定了部分电极过程参数,并发现多菌灵氧化峰电流的一阶导数值与其浓度在5.0×10~(-6)～1.0×10~(-4) mol/L范围内呈线性关系,回归方程为:I_p ′(A)=-3.112×10~(-6)-1.198c(mol/L),R=-0.9953,其检出限为2.0×10~(-7) mol/L,回收率为99.0%～105.6%.     

Fe(CN)$\rm{ {_{6}^{4-}}}$‐Doped‐Glutaraldehyde‐Cross‐Linked Poly‐L‐Lysine Film Electrode. Part 1: Electrochemical Characterization and Its Electrocatalytic Activity Towards Oxidation of Ascorbic Acid

The present work describes preparation, characterization, and electrocatalytic behavior of a hexacyanoferrate‐doped‐glutaraldehyde‐cross‐linked poly‐L ‐lysine (PLL‐GA‐Fe(CN) film modified glassy carbon electrode. The modified electrode has been successfully prepared by electrostatically binding negatively charged Fe(CN) mediator into cross‐linked poly‐L ‐lysine cationic film. The dependence of the peak current of the modified electrode in pure supporting electrolyte (pH 6.8 phosphate buffer solution; PBS) shows that the charge transport in the film is fast and relatively unimpeded at lower scan rates. Cyclic voltammetry and rotating disk electrode (RDE) techniques are used to investigate the electrocatalytic activity of modified electrode towards oxidation of ascorbic acid. The rate constant (k), of catalytic reaction between electrogenerated Fe(CN) ions and ascorbic acid, obtained from RDE analysis was found to be 5.53×10⁵ cm³ mol^?1 s^?1. Finally, the PLL‐GA‐Fe(CN) film electrodes are successfully used for the individual estimation of ascorbic acid in the concentration range of physiological interest.     

Amperometric sensing of NADH and ethanol using a hybrid film electrode modified with electrochemically fabricated zirconia nanotubes and poly (acid fuchsin)

We report on a glassy carbon electrode (GCE) modified with a film of chitosin containing acid fuchsin (AF) adsorbed onto zirconia nanotubes. The mixture was polymerized by cyclic voltammetric scannings in the potential range from - 0.8?V to +1.3?V in buffer solution to produce a hybrid film electrode (nano-ZrO₂/PAF/GCE). The morphology of the hybrid film electrode surface was characterized by scanning electron microscopy. Its electrochemical properties were studied via electrochemical impedance spectroscopy. The electrochemical response of nicotinamide adenine dinucleotide (NADH) was investigated by differential pulse voltammetry and amperometry. The results indicated that the nano-ZrO₂/PAF/GCE possesses well synergistic catalytic activity towards NADH. Compared to an unmodified GCE, the oxidation overpotential is negatively shifted by 224?mV, and the oxidation current is significantly increased. Under optimal conditions, the amperometric response is linearly proportional to the concentration of NADH in the 1.0 – 100.0?μM concentration range. Ethanol also can be determined by amperometry if alcohol dehydrogenase and NADH are added to the sample. Two linear relationships between current and alcohol concentration were obtained. They cover the range from 0.03 to 1.0?mM, and from 1.0 to 12.0?mM.

Direct Electrochemistry and Electrocatalysis of the Hemoglobin Immobilized on Diazonium‐Functionalized Aligned Carbon Nanotubes Electrode

A simple and efficient electrochemical method is utilized to functionalize aligned carbon nanotubes (ACNTs) by the electrochemical reduction of 4‐carboxyphenyl diazonium salt. Thus hemoglobin (Hb) molecules were covalently immobilized on the diazonium‐ACNTs surface via carbodiimide chemistry. Direct electrochemistry and bioelectrocatalytic activity of the immobilized Hb were then investigated by cyclic voltammetry (CV) and amperometry techniques. It is showed that the Hb film on the diazonium‐ACNTs electrode had well‐defined redox peaks with a formal potential (E°) at ?312 mV (vs. Ag/AgCl), and the Hb‐ACNTs electrode displayed good electrocatalytic activity to H₂O₂ reduction. Owing to the high Hb covering on the ACNTs surface (Γ*=2.7×10^?9 mol cm^?2), the catalytic current were significantly improved when compared to the current measured at an Hb‐tangled carbon nanotubes electrode. The Hb‐ACNTs electrode exhibited high sensitivity, long‐term stability and wide concentration range from 40 μM to 3 mM for the amperometric detection of H₂O₂. The heterogeneous reaction rate constant (k_s) was 0.95±0.05 s^?1 and the apparent Michaelis–Menten constant (K was 0.15 mM.     

阿昔洛韦在硼掺杂金刚石电极上的电化学行为及其与DNA相互作用的研究

利用硼掺杂金刚石(BDD)电极通过循环伏安法和微分脉冲伏安法研究了阿昔洛韦在0.10 mol/L磷酸盐缓冲溶液(pH 7.4)中的电化学行为及其与DNA的相互作用.与玻碳电极相比,阿昔洛韦在BDD电极上的循环伏安曲线在1.17 V处的氧化峰电流更大,背景电流较低.根据峰电位随溶液pH值和扫描速率的变化趋势考察了阿昔洛韦...     

Amperometric Detection of Dopamine in the Presence of Ascorbic Acid Using a Nafion Coated Glassy Carbon Electrode Modified with Catechin Hydrate as a Natural Antioxidant

Catechin hydrate (trans-3,3,4,5,7-penta-hydroxyflavone) is a derivative of catechol, and it is one of the natural antioxidant and anticarcinogenic compounds found in many fruits and agricultural foods. A new electrode was prepared by electrodeposition of a catechin-hydrate film on the surface of an activated glassy carbon electrode, followed by coating with nafion layer. Cyclic voltammetry was used for the deposition process, and the resulting modified electrode was found to retain the activity of the quinone/hydroquinone group anticipated for a surface-immobilized redox couple. The cyclic voltammograms of the modified electrode indicated that the surface-confined catechin-hydrate was strongly dependent on the solution pH. The electrochemical behaviour and stability of the modified electrode were studied by cyclic voltammetry. The apparent charge transfer rate constant (k _s ) and electron transfer coefficient () between the electrode surface and adsorbed catechin hydrate were calculated as 0.41 and 0.31s^z–1 0.31, respectively. The modified electrode exhibits an electrocatalytic effect on dopamine oxidation in the pH range of 2 to 7. The modified electrode was used for the electrocatalytic oxidation of dopamine in the presence of ascorbic acid and the elimination of the interference by ascorbic acid (AA) when present in a 200-fold concentration excess. A very large decrease (400mV) in the overpotential for the oxidation of dopamine and current increase were observed on the surface of the modified electrode. Dopamine was determined amperometrically at the modified electrode in the concentration range of 100nM to 0.1mM. The detection limit (signal to noise is 3) and sensitivity are 11nM and 16nA/µM, respectively. The modified electrode was employed to determine DA in biological mediums.     

Voltammetric study on the complex of thiram-copper(II) and its application

Based on the formation of tetramethylthiuram disulfide (thiram)-copper(II) complex by square-wave voltammetry on a glassy carbon electrode, a new method is proposed for determination of thiram. There is a good linear relationship between peak current and concentration of thiram in the range of  mol l⁻¹ (r=0.999). The method is applied to the determination of thiram residue in plant with satisfactory results, compared with results achieved by using HPLC. Two oxidation peaks and two reduction peaks are obtained by cyclic voltammetry on a glassy carbon electrode in 0.2 mol l⁻¹ HAc-NaAc (pH 4.0) solution containing thiram-copper(II) complex. The electrode reaction process is quasi-reversible with adsorptive characteristics. The mechanism of electrode reaction is discussed.     

Simultaneous and Sensitive Detection of Cd(II) and Pb(II) Using a Novel Bismuth Film/Ordered Mesoporous Carbon‐molecular Wire Modified Graphite Carbon Paste Electrode

An electrochemical sensor for the simultaneous and sensitive detection of Cd(II) and Pb(II) is proposed on the basis of square‐wave anodic stripping voltammetry (SWASV) experiments using a novel bismuth film/ordered mesoporous carbon‐molecular wire modified graphite carbon paste electrode (Bi/OMC‐MW/GCPE). Ordered mesoporous carbon (OMC) and molecular wire (MW) (diphenylacetylene) were used as the modifier and binder, respectively. The Bi/OMC‐MW/GCPE was prepared with the addition of graphite powder, OMC and DPA at the ratio of 2 : 1 : 1. The electrochemical properties and morphology of the electrode were characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), SWASV and scanning electron microscopy (SEM). The parameters affecting the stripping current response were investigated and optimized. The experimental results show that the prepared electrode exhibited excellent electrochemical performance, good electrical conductivity and a high stripping voltammetric response. Under optimized conditions, a linear range was achieved over a concentration range from 1.0 to 70.0 μg/L for both Cd(II) and Pb(II) metal ions, with detection limits of 0.07 μg/L for Cd(II) and 0.08 μg/L for Pb(II) (S/N=3) with the deposition time 150 s. Moreover, the sensor exhibited improved sensitivity and reproducibility compared to traditional CPEs. The fabricated electrode was then successfully used to satisfactorily detect Cd(II) and Pb(II) in real soil samples.     

Selective detection and recovery of gold at tannin-immobilized non-conducting electrode

A tannin-immobilized glassy carbon electrode (TIGC) was prepared via electrochemical oxidation of the naturally occurring polyphenolic mimosa tannin, which generated a non-conducting polymeric film (NCPF) on the electrode surface. The fouling of the electrode surface by the electropolymerized film was evaluated by monitoring the electrode response of ferricyanide ions as a redox marker. The NCPF was permselective to HAuCl₄, and the electrochemical reduction of HAuCl₄ to metallic gold at the TIGC electrode was evaluated by recording the reduction current during cyclic voltammetry measurement. In the mixed electrolyte containing HAuCl₄ along with FeCl₃ and/or CuCl₂, the NCPF remained selective toward the electrochemical reduction of HAuCl₄ into the metallic state. The chemical reduction of HAuCl₄ into metallic gold was also observed when the NCPF was inserted into an acidic gold solution overnight. The adsorption capacity of Au(III) on tannin-immobilized carbon fiber was 29 ± 1.45 mg g⁻¹ at 60 °C. In the presence of excess Cu(II) and Fe(III), tannin-immobilized NCPF proved to be an excellent candidate for the selective detection and recovery of gold through both electrochemical and chemical processes.     

Electrocatalysis of Tryptophan at Multi-Walled Carbon Nanotube Modified Electrode

Acid-treated multi-walled carbon nanotubes (MWNTs) were immobilized on the surface of a glassy carbon electrode to form an MWNT-modified electrode. The electrocatalytic response of the modified electrode towards tryptophan (Trp) was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results demonstrated that the modified electrode exhibited a high degree of catalytic activity towards the oxidation of Trp. An oxidation peak was obtained in Trp solution at the MWNT-modified electrode. Compared with a bare electrode, the peak current had obviously increased, and the peak potential had shifted in a negative direction. However, under the same conditions, no response was observed for other amino acids. The oxidation peak currents were proportional linearly to the concentration of Trp, a property which could be utilized to detect Trp. The determination conditions, such as the concentration, the composition and the pH values of the supporting electrolyte, accumulation time, as well as scan rate etc. were optimized. Under the chosen conditions, the DPV peak current is linear to the concentration of Trp in the range of 2.5×10^–7 to 1.0×10^–4molL^–1, and the detection limit is 2.7×10^–8molL^–1. Moreover, the detection is free of interference from other amino acids. The modified electrode has been successfully applied to determine the concentration of Trp in composite amino acid injections, and it displays excellent repeatability and higher sensitivity.     

DNA/聚(3,4-乙烯基二氧噻吩)修饰电极的制备及其用于亚硝酸根的电化学行为及测定研究

采用恒电流和电沉积两步法制备了脱氧核糖核酸-聚(3,4-乙烯基二氧噻吩)(DNA-PEDOT)复合膜修饰玻碳电极。用电化学阻抗法(EIS)和循环伏安法(CV)表征了不同修饰电极的修饰可行性和表面的电子传递能力。结果表明,DNA可以牢固地结合在PEDOT膜上,并能改善PEDOT膜的性质。研究了NO2-在DNA-PEDOT修饰电极上的电化学行为,提出了一种新的检测NO2-的电化学方法。在0.1 mol/L pH7.0的磷酸盐缓冲溶液(PBS)中,NO2-在DNA-PEDOT修饰电极上于0.88 V左右出现1个较好的氧化峰,考察了该氧化峰的性质及其影响因素。示差脉冲伏安法(DPV)的结果表明,NO2-的DPV氧化峰电流与其浓度在0.3~1.0、1.0~20、20~100μmol/L 3个范围内呈良好的线性关系,检出限(S/N=3)为60 nmol/L,并考察了可能存在的干扰物质对测定的影响。结果显示,该复合膜修饰电极对NO2-的检测具有良好的稳定性和选择性。将其用于实际样品的检测,结果满意。     

Carbon black nanoparticles film electrode prepared by using substrate-induced deposition approach

A new type of carbon film electrode, composed of a thin layer of tightly packed carbon black (CB) nanoparticles deposited onto a gelatin-covered indium tin oxide/glass support using the surface-induced deposition (SID) approach, is presented. Some parameters of the novel SID method were optimized and the surface image and functionalization of the investigated carbon black film electrode (CBFE) was inspected by employing scanning electron microscopy and infrared spectroscopy. A cyclic voltammetry (CV) study was conducted in which the electron-transfer kinetics and CBFE interfacial characteristics were evaluated employing several selected reference redox systems, such as [Ru(NH₃)₆]^3+/2+, [Fe(CN)₆]^3−/4− and Fe^3+/2+ in aqueous, and ferrocene/ferrocenium in acetonitrile media. CV recordings were also performed in order to compare the electrochemical behavior of the CBFE with that of some well-known and established bare carbon-based electrodes. In order to confirm the validity of the CB film preparation method, the electroanalytical performance of the proposed CBFE was examined by carrying out linear sweep voltammetry of ascorbic acid (AA), anodic stripping square-wave voltammetry of Cu(II) in acidic medium, and amperometric measurements of hydrogen peroxide under flow injection conditions. The sensing characteristics of the novel carbon film electrode, demonstrated in this preliminary study, comprise: (i) a wide working potential window ranging from +1.0 to −1.3 V (depending on the solution pH), (ii) a wide applicable pH range (at least from 2 to 12), (iii) low voltammetric background (<5 μA cm⁻²), (iv) a satisfactory linear voltammetric and amperometric response (r² > 0.99) to various analytes, (v) good reproducibility (for example, r.s.d. of 2% in amperometric detection of H₂O₂ and r.s.d. of 8.5% for electrode-to-electrode CV runs), and (vi) stable and fast current response (at least 100 CV runs with negligible change in CV response). The main advantages of the proposed CBFE originate from the unique CB film formation procedure that enables fast, simple, inexpensive and non-toxic CBFE preparation, which can find application in advanced electrochemical devices and is suitable for mass production.     

Study on the Indirect Electrochemical Detection of Ammonium Ion with In Situ Electrogenerated Hypobromous Acid

The electrochemical oxidation of bromide in the presence of ammonium ion (NH ) was studied by cyclic voltammetry and UV‐vis spectroscopy. The experimental results suggested that the anodically generated bromine (Br₂) would be hydrolyzed to hypobromous acid (HBrO) at the pH range of 5–7 and was further disproportionate to hypobromite anion (BrO^?) when pH was larger than 7. Both HBrO and BrO^? were confirmed to be participated in the following homogeneous chemical reaction with the coexisted ammonium ion. However, HBrO is electroactive whereas BrO^‐ is electroinactive at carbon electrode. Based upon the reaction of HBrO with NH , an indirect electrochemical method was proposed for determination of NH with dual‐electrode configuration in phosphate buffer solution (pH 7), where HBrO was produced at a generator electrode and the excess HBrO was subsequently detected at a collector electrode after a reaction with NH in a batch solution or in a micro flow injection analytical (micro‐FIA) system by using an interdigitated array (IDA) Pt microelectrode and a carbon film ring‐disk electrode (CFRDE), respectively. The decreasing of reduction current at the collector electrode was proportional to the concentration NH in both systems, with the detection limit below 3.0 μM. This approach shows the advantage of highly selectivity even in presence of a large amount of coexisted cations, and was successfully applied for the determination of NH in environmental water samples.     

Simultaneous detection of ascorbate and uric acid using a selectively catalytic surface

The direct and selective detection of ascorbate at conventional carbon or metal electrodes is difficult due to its large overpotential and fouling by oxidation products. Electrode modification by electrochemical reduction of diazonium salts of different aryl derivatives is useful for catalytic, analytical and biotechnological applications. A monolayer of o-aminophenol (o-AP) was grafted on a glassy carbon electrode (GCE) via the electrochemical reduction of its in situ prepared diazonium salts in aqueous solution. The o-aminophenol confined surface was characterized by cyclic voltammetry. The grafted film demonstrated an excellent electrocatalytic activity towards the oxidation of ascorbate in phosphate buffer of pH 7.0 shifting the overpotential from +462 to +263 mV versus Ag/AgCl. Cyclic voltammetry and d.c. amperometric measurements were carried out for the quantitative determination of ascorbate and uric acid. The catalytic oxidation peak current was linearly dependent on the ascorbate concentration and a linear calibration curve was obtained using d.c. amperometry in the range of 2-20 μM of ascorbate with a correlation coefficient 0.9998, and limit of detection 0.3 μM. The effect of H₂O₂ on the electrocatalytic oxidation of ascorbate at o-aminophenol modified GC electrode has been studied, the half-life time and rate constant was estimated as 270 s, and 2.57 × 10⁻³ s⁻¹, respectively. The catalytically selective electrode was applied to the simultaneous detection of ascorbate and uric acid, and used for their determination in real urine samples. This o-AP/GCE showed high stability with time, and was used as a simple and precise amperometric sensor for the selective determination of ascorbate.     

纳米金/双氢氧化物膜修饰电极制备及对肾上腺素的测定

研究了纳米金/双氢氧化物膜修饰玻碳电极(AuNPs/LDHs/GCE)的制备,通过循环伏安法、扫描电镜和电化学阻抗对修饰电极进行了表征;详细讨论了电极的性能,找出了制备该修饰电极的实验条件,并将此电极用于生物体系中肾上腺素(Adrenaline,AD)的电化学测定.在选定的实验条件下,修饰电极在磷酸盐缓冲溶液(pH=7.0)中进行循环伏安扫描时,氧化峰电流和肾上腺素浓度在9.0×10-8～1.0×10-4mol/L范围内呈良好的线性关系,相关系数为0.9982,其检出限(S/N=3)可达3.1×10-8 mol/L.据此建立了一种新的测定肾上腺素的分析方法,可用于实际样品的检测.     

葡萄糖在碳纳米管/纳米TiO2膜载Pt复合电极上的电催化氧化

用电化学循环伏安法和计时电位法研究了葡萄糖在碳纳米管／纳米TiO2膜载Pt(CNT／nano-TiO2／Pt)复合电极上的电催化氧化,结果表明,在碱性介质中CNT／nano-TiO2／Pt复合电极对葡萄糖的电氧化具有高催化活性,葡萄糖氧化峰电流密度高达13mA／cm^2,比铂电极上的增大一倍;复合电极性能稳定,抗中毒能力强,不易发生氧化振荡,是葡萄糖燃料电池和葡萄糖传感器的高活性催化电极。     

Electrochemical Preparation of Poly(acriflavine) Film‐Modified Electrode and Its Electrolcatalytic Properties Towards NADH,Nitrite and Sulfur Oxoanions

Electrochemical polymerization of acriflavine (AF) was carried out onto glassy carbon electrodes (GCE) from the aqueous buffer solution containing 1.5×10^?3 M AF monomer (pH 3.5) which produced a thin electrochemically active film. This is noted as poly(AF) film modified electrodes (PAF/GCE). This modified electrode was shown a stable reversible redox couple centered at +0.22 V in pH 3.5 buffer solutions. PAF/GCE was found to be more stable in acidic solutions and its formal potential was found to be pH dependent with a slope close to ?60 mV/pH. The electrochemical deposition kinetics of poly(AF) onto gold coated quartz crystal was studied by using electrochemical quartz crystal microbalance (EQCM) combined with cyclic voltammetry (CV). PAF/GCE was found be good mediator for electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) in pH 5 buffer solutions. The electrocatalytic oxidation of SO and electrocatalytic reduction of NO , SO and S₂O were carried out at PAF/GCE electrode in acidic aqueous solutions. The electrocatalytic oxidation of NADH was also investigated by using amperometric method.