铁氰化钆修饰电极的固态电化学及电催化性能

制备了一种新的稀土铁氰化物——铁氰化钆(GdHCF), 并对其进行了表征. 元素分析、EDX和TGA结果表明, GdHCF的计量式为NaGdFe(CN)6•12H2O(在NaCl溶液中制备), 红外光谱结果显示GdHCF晶体中有两种形式的水分子存在, 一种是靠氢键结合的填隙水分子(5个), 一种是与Gd配位的配位水分子(7个)；XPS结果表明GdHCF中铁为+2价, 钆为+3价. 将GdHCF固定到石墨(SG)电极上(GdHCF/SG), 研究了它的固态电化学性能, 其循环伏安曲线上表现出一对良好且稳定的氧化还原峰, 式量电位E0′几乎不随扫速而变化(在10~300 mV•s−1范围内, E0′平均值为(197±3) mV)；并且E0′与支持电解质中阳离子(Na+)活度的对数(lgaNa+)之间呈线性关系, 斜率为54.1 mV, 这一特性关系可用于测定NaCl溶液中Na+的活度. 进一步研究的结果表明, GdHCF对神经递质多巴胺(DA)和抗坏血酸(AA)的电化学氧化均具有催化作用, 催化电流随DA(或AA)浓度的增加而增加.     

Electrochemical application of titanium dioxide nanoparticle/gold nanoparticle/multiwalled carbon nanotube nanocomposites for nonenzymatic detection of ascorbic acid

Titanium dioxide nanoparticle/gold nanoparticle/carbon nanotube (TiO₂/Au/CNT) nanocomposites were synthesized, and then characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDX). A TiO₂/Au/CNT nanocomposite-modified glassy carbon (GC) electrode was prepared using the drop coating method and was investigated using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), differential pulse voltammetry (DPV), and amperometric current–time response (I-T). The modified material is redox-active. The nonenzymatically detected amount of ascorbic acid (AA) on the TiO₂/Au/CNT electrode showed a linear relationship with the AA concentration, for concentrations from 0.01 to 0.08 μM; the sensitivity was 117,776.36 μA?·?cm^?2?·?(mM)^?1, and the detection limit was 0.01 μM (S/N?=?3). The results indicated that the TiO₂/Au/CNT nanocomposite-modified GC electrode exhibited high electrocatalytic activity toward AA. This paper describes materials consisting of a network of TiO₂, Au, and MWCNTs, and the investigation of their synergistic effects in the detection of AA.     

铁氰化钆修饰电极的制备及表征

应用电化学循环扫描法于玻碳电极表面沉积并形成铁氰化钆修饰电极(GdHCF/GC),扫描电镜(SEM)显示,有两种大小和外形明显不同的颗粒状GdHCF附着在电极表面.红外光谱表明,GdCHF的C≡N弯曲振动吸收峰出现在2062.5 cm-1处.循环伏安法测试表明,在0.2 mol/L NaC l溶液中,GdHCF/GC电极出现两对氧化还原峰,扫速为20 mV/s时,其氧化还原峰的式量电位分别为E0’(I)=192.5 mV和E0’(II)=338.5 mV.研究了不同支持电解质对GdHCF/GC电极电化学性能的影响,GdHCF对Na+离子有优先选择性.     

Electrochemical Properties of Th(IV)‐Hexacyanoferrate Sol‐Gel Carbon Composite Electrode: Electrocatalytic Oxidation of Dopamine and Ascorbic Acid

A new sol‐gel carbon composite electrode using hexacyanoferrate (HCF)‐Th(IV) ion pair as a suitable modifier is fabricated in the present study. The Th(IV)‐HCF‐sol‐gel carbon composite electrode (THCF‐CCE) has been prepared by mixing methyl trimethoxysilan (MTMOS) sol‐gel precursor and carbon powder with ion pair and then to fix in a plastic tube. Cyclic voltammetry and chronoamperometry were employed to study the electrochemical and electrocatalytic properties of proposed electrode. The apparent charge transfer rate constant, k_s, and transfer coefficient, α, for electron transfer between ion‐pair and sol‐gel CPE were calculated as 3.10 ± 0.10 s^?1 and 0.52, respectively. The THCF‐CCE showed a significant electrocatalytic activity towards oxidation of ascorbic acid (AA) and dopamine (DA) in 0.1 M acidic phosphate buffer solutions (pH 3) containing KCl as a supporting electrolyte. The mean value of the diffusion coefficients for ascorbic acid and dopamine were found 4.12 × 10^?5 and 4.43 × 10^?5 (cm²s^?1), respectively. High stability, good reproducibility, rapid response, easy surface regeneration and fabrication are the important characteristics of the proposed sensor. The resulting peaks from the electrocatalytic oxidation of AA and DA were well resolved with good sensitivity. A linear response was observed for AA and DA in the concentration range of 1 × 10^?5 to 3 × 10^?3 M and 4 × 10^?6 to 2.2 × 10^?4 M, respectively.     

基于分子的六氰合铁酸钴纳米粒子：合成，表征及其电化学性质

采用直接混合法制得平均尺寸小于50 nm的六氰合铁酸钴纳米粒子，元素分析表明其计量学分子式为K_0.2Co_1.4[Fe(CN)₆]•xH₂O，红外光谱证明此物质是由铁磁性的Co^II_1.5[Fe^III(CN)₆]和反铁磁性的KCo^III[Fe^II(CN)₆]组成，并含有一定量的结晶水。用六氰合铁酸钴纳米粒子修饰的玻碳电极具有良好的稳定性和可逆的循环伏安行为，其电化学特征受溶液中配对阳离子种类和支持电解质浓度的影响。作为电极表面的媒介体，该薄膜对多巴胺的氧化还原具有电催化作用。     

Catalytic Oxidation of Dopamine at a Nickel Hexacyanoferrate Surface Modified Graphite Wax Composite Electrode Coated with Nafion

A chemically modified electrode was successfully fabricated by means of depositing a thin layer of nickel hexacyanoferrate (NiHCF) on an amine adsorbed graphite paraffin wax composite electrode using a new approach. The electrode was further coated with Nafion. The electrochemical characteristics of the modified electrode were studied using cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The modified electrode catalyzed dopamine (DA) oxidation in the concentration range of 1.5×10^?6 to 1.2×10^?3 M without the interference from ascorbic acid (AA). A detection limit of 4.9×10^?7 M was obtained for DA in the presence of AA with a correlation coefficient of 0.9972 based on S/N=3. Flow injection analysis was used for the determination of dopamine with excellent reproducible results. The analytical utility of the sensor was evaluated for detection of DA in urine.     

Simultaneous Detection of Dopamine and Uric Acid under Coexistence of Ascorbic Acid with DNA/Pt Nanocluster Modified Electrode

A novel biosensor by electrochemically codeposited Pt nanoclusters and DNA film was constructed and applied to detection of dopamine (DA) and uric acid (UA) in the presence of high concentration ascorbic acid (AA). Scanning electron microscopy and X‐ray photoelectron spectroscopy were used for characterization. This electrode was successfully used to resolve the overlapping voltammetric response of DA, UA and AA into three well‐defined peaks with a large anodic peak difference (ΔE_pa) of about 184 mV for DA and 324 mV for UA. The catalytic peak current obtained from differential pulse voltammetry was linearly dependent on the DA concentration from 1.1× 10^?7 to 3.8×10^?5 mol·L^?1 with a detection limit of 3.6×10^?8 mol·L^?1 (S/N=3) and on the UA concentration from 3.0×10^?7 to 5.7×10^?5 mol·L^?1 with a detection limit of 1.0×10^?7 mol·L^?1 with coexistence of 1.0×10^?3 mol·L^?1 AA. The modified electrode shows good sensitivity and selectivity.     

Chitosan Incorporating Cetyltrimethylammonium Bromide Modified Glassy Carbon Electrode for Simultaneous Determination of Ascorbic Acid and Dopamine

Simultaneous determination of a neurotransmitter, dopamine (DA), and ascorbic acid (AA) is achieved at neutral pH on a chitosan incorporating cetyltrimethylammonium bromide (CTAB) modified glassy carbon (GC) electrode. Differential pulse voltammetry (DPV) technique was used to investigate the electrochemical response of DA and AA at a glassy carbon electrode modified with chitosan incorporating CTAB. An optimum 6.0 mmol L^?1 of CTAB together with 0.5 wt% of chitosan was used to improve the resolution and the determination sensitivity. In 0.1 mol L^?1 aqueous phosphate buffer solution of pH 6.8, the chitosan‐CTAB modified electrode showed a good electrocatalytic response towards DA and AA. The anodic peak potential of DA shifted positively, while that of AA shifted negatively. Thus, the difference of the anodic peaks of DA and AA reached 0.23 V, which was enough to separate the two anodic peaks very well. The presented method herein could be applied to the direct simultaneous determination of DA and AA without prior treatment. The anodic peak currents (I_pa) of DPV are proportional to DA in the concentration range of 8 μM to 1000 μM, to that of AA 10 μM to 2000 μM, with correlation coefficients of 0.9930 and 0.9945, respectively. The linear range is much wider than previously reported.     

Direct Electrochemistry and Electrocatalysis of Hemoglobin Based on Nafion‐Room Temperature Ionic Liquids‐Multiwalled Carbon Nanotubes Composite Film

A robust and effective composite film combined the benefits of Nafion, room temperature ionic liquid (RTIL) and multi‐wall carbon nanotubes (MWNTs) was prepared. Hemoglobin (Hb) was successfully immobilized on glassy carbon electrode surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Hb were investigated in detail. A pair of well‐defined and quasi‐reversible redox peaks of Hb was obtained in 0.10 mol·L^?1 pH 7.0 phosphate buffer solution (PBS), indicating that the Nafion‐RTIL‐MWNTs film showed an obvious promotion for the direct electron transfer between Hb and the underlying electrode. The immobilized Hb exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0×10^?6 to 2.5×10^?4 mol·L^?1, with a detection limit of 8.0×10^?7 mol·L^?1 (S/N=3). The apparent Michaelis‐Menten constant (K_m^app) was calculated to be 0.34 mmol·L^?1. Moreover, the modified electrode displayed a good stability and reproducibility. Based on the composite film, a third‐generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Electrochemical properties of ordered mesoporous carbon and its electroanalytical application for selective determination of dopamine

The electrochemical properties of one novel carbon material, ordered mesoporous carbons (OMC), synthesized by templating SBA-15 mesoporous silica materials and the electrocatalytic behaviors of OMC modified electrode towards the oxidation of dopamine (DA) and ascorbic acid (AA) were studied. Cyclic voltammetry was used to evaluate the electrochemical behaviors of OMC in 5 mM K₃Fe(CN)₆/0.1 M KCl solution. OMC showed a faster electron transfer rate, as compared with glass carbon (GC) electrode. The higher electron transfer kinetics can be attributed to the existence of a large amount of edge plane defect sites in the OMC materials, which was verified by Raman spectroscopy. The cyclic voltammetric studies also showed the presence of oxygen-containing functional groups on the surface of OMC. Furthermore, the OMC modified electrode showed high electrocatalytic activities toward the oxidation of DA and AA, and resolved their voltammetric responses into two well-defined peaks with peak separation of ca. 0.210 V. The OMC modified electrode could be effectively used for the selective electrochemical determination of DA in the presence of AA.     

Electrocatalytic Oxidation of Dopamine by Ferrocene in Lipid Film Cast on a Glassy Carbon Electrode

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Four Gadolinium Coordination Compounds Derived from Various Tetrazole‐Containing Carboxylic Acids

Reactions of four different tetrazole‐containing carboxylic acids with GdCl₃ · 6H₂O, produced the coordination compounds, [Gd₄(pytza)₅(H₂O)₁₀(μ‐O) Cl] · 4H₂O · 2Cl ( 1 ) [pytza = 2‐(5‐(pyridine‐4‐yl)‐2H‐tetrazole‐2‐yl)acetato], [Gd(pztza)₂(H₂O)₆] · pztza · 3H₂O ( 2 ), [pztza = 2‐(5‐(pyrazin‐2‐yl)‐2H‐tetrazol‐2‐yl) acetato], [Gd(pmtza)₂(H₂O)₆]Cl · 2H₂O ( 3 ), [pmtza = 2‐(5‐(pyrimidyl‐2‐yl)‐2H‐tetrazol‐2‐yl) acetato], and Gd(tzpya)₂(H₂O)₅]Cl · 4H₂O ( 4 ) [tzpya = 2‐(4‐(5H‐tetrazol‐5‐yl)pyridin‐1(4H)‐yl) acetato]. The compounds were structurally characterized by elemental analysis, IR spectroscopy, and single‐crystal X‐ray diffraction. X‐ray diffraction analysis reveals that compound 1 displays a 2D single layered network and compounds 2 – 4 are mononuclear. Compounds 1 – 4 are self‐assembled to form 3D networks by hydrogen bonding interactions. Furthermore, the luminescent properties in the solid state at room temperature were investigated.     

Electrodeposition CaCO3 Nanoparticles‐chitosan Composite Film on Carbon Ionic Liquid Electrode as a Platform for Hemoglobin Electrochemical Biosensor

By one‐step co‐electrodeposition CaCO₃ nanoparticles‐chitosan composite film on carbon ionic liquid electrode (CILE), and then by spreading the composition of hemoglobin (Hb) and chitosan on the nanoCaCO₃‐chi/CILE, a Hb‐chi/nanoCaCO₃‐chi/CILE was fabricated and the direct electrochemistry and electrocatalysis of Hb at the electrode was investigated. The electrochemical impedance spectroscopy of the modified electrode showed the electron transfer resistance was 1166 Ω. Investigation results of cyclic voltammetrys showed a pair of well‐defined and quasireversible redox peak of Hb with the formal potentials of ‐0.295 V (vs. SCE) in 0.1 mol·L^‐1 pH 7.0 PBS; the response time of the reduction peak currents of Hb was lower than 3s; a linear range for determination of H₂O₂ was from 5.0 μmol·L^‐1 to 1.3 mmol·L^‐1 with a detection limit of 1.6 μmol·L^‐1 (S/N = 3) and a sensitivity of 0.16 A·M^‐1·cm^‐2; the electron transfer rate constant and the apparent Michaelis‐Menten constant of Hb were 1.98 s^‐1 and 0.81 mmol·L^‐1, respectively. As a result, the case of the one‐step co‐electrodeposition and the promising feature of biocomposite could serve as a versatile platform for the fabrication of electrochemical biosensors.     

Selective Electroanalysis of Ascorbic Acid Using a Nickel Hexacyanoferrate and Poly(3,4‐ethylenedioxythiophene) Hybrid Film Modified Electrode

The mixed‐valent nickel hexacyanoferrate (NiHCF) and poly(3,4‐ethylenedioxythiophene) (PEDOT) hybrid film (NiHCF‐PEDOT) was prepared on a glassy carbon electrode (GCE) by multiple scan cyclic voltammetry. The films were characterized using atomic force microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X‐ray diffraction, and electrochemical impedance spectroscopy (AC impedance). The advantages of these films were demonstrated for the detection of ascorbic acid (AA) using cyclic voltammetry and amperometric techniques. The electrocatalytic oxidation of AA at different electrode surfaces, such as the bare GCE, the NiHCF/GCE, and the NiHCF‐PEDOT/GCE modified electrodes, was determined in phosphate buffer solution (pH 7). The AA electrochemical sensor exhibited a linear response from 5×10⁻⁶ to 1.5×10⁻⁴ M (R²=0.9973) and from 1.55×10⁻⁴ to 3×10⁻⁴ M (R²=0.9983), detection limit=1×10⁻⁶ M, with a fast response time (3 s) for AA determination. In addition, the NiHCF‐PEDOT/GCE was advantageous in terms of its simple preparation, specificity, stability and reproducibility.     

Electrochemical Preparation and Characterization of Neodymium Hexacyanoferrate and Its Application

A novel route for the fabrication of neodymium hexacyanoferrate (NdHCF) modified glassy carbon electrodes (GCE) was proposed. The morphological characterization of NdHCF was examined by scanning electron microscopy (SEM) and Fourier transform infrared spectra (FTIR). The performances of the NdHCF/GCE were characterized with cyclic voltammetry and differential pulse voltammograms (DPV). The modified electrode showed excellent electrocatalytic effect and high stability toward the electrochemical oxidation of dopamine (DA) in phosphate buffer solution (pH 5.5) with a diminution of the anodic overpotential of 155 mV. The anodic peak currents increased linearly with the concentration of DA from 5.0×10^?7 to 6.0×10^?4 M with a detection limit of 1.0×10^?8 M (S/N=3). The most important is that the modified electrode could be used for the determination of DA in the presence of an ascorbic acid concentration as large as 100‐fold that of DA. The proposed method was used to determine DA in DA‐hydrochloride injection and showed excellent sensitivity and recovery. The ease of fabrication, high stability, and low cost of the modified electrode are the promising features of the proposed sensor.     

Preparation, Electrochemical Behavior and Electrocatalytic Activity of a Copper Hexacyanoferrate Modified Ceramic Carbon Electrode

A copper hexacyanoferrate modified ceramic carbon electrode （CuHCF/CCE） had been prepared by two-step sol-gel technique and characterized using electrochemical methods. The resulting modified electrode showed a pair of well-defined surface waves in the potential range of 0.40 to 1.0 V with the formal potential of 0.682 V （vs. SCE） in 0.050 mol·dm^-3 HOAc-NaOAc buffer containing 0.30 mol·dm^-3 KCl. The charge transfer coefficient （a） and charge transfer rate constant （ks） for the modified electrode were calculated. The electrocatalytic activity of this modified electrode to hydrazine was also investigated, and chronoamperometry was exploited to conveniently determine the diffusion coefficient （D） of hydrazine in solution and the catalytic rate constant （kcat）. Finally, hydrazine was determined with amperometry using the resulting modified electrode. The calibration plot for hydrazine determination was linear in 3.0 × 10^-6--7.5 × 10^-4 mol·dm^-3 with the detection limit of 8.0 × 10^-7 molodm^-3. This modified electrode had some advantages over the modified film electrodes constructed by the conventional methods, such as renewable surface, good long-term stability, excellent catalytic activity and short response time to hydrazine.     

铁氰化锰修饰玻碳电极的制备及其电化学性能

A thin film of manganese hexacyanoferrate （MnHCF） was electrochemically formed on a glassy carbon （GC） electrode to prepare a chemically modified electrode （CME）. The mechanism of film formation of MnHCF and its growth process were investigated in detail by cyclic voltammetry. The results show that the stoichiometric composition of MnHCF is Mn^ⅢFe^Ⅲ（CN）6, an analogue of prussian yellow. There exist three clear-cut stages in the whole modification process and the last stage is indispensable to the fabrication of homogenized, stable MnHCF film and must last for an appropriate time. The surface morphology of MnHCF/GC electrode was characterized by scanning electron microscopy （SEM）, which further verified the effective deposition of MnHCF film on GC. The kinetic constants of MnHCF/GC electrode process were also evaluated. The resulting MnHCF film modified electrode presented good stability and high electrocatalytic activity toward the oxidation of H2O2, indicating that MnHCF film possesses function of catalase and can be expected for analytical purposes.     

Gold nanoparticles on a thiol-functionalized silica network for ascorbic acid electrochemical detection in presence of dopamine and uric acid

A simple preparation methodology able to stabilize gold nanoparticles and to obtain an electrode which detects ascorbic acid, uric acid, and dopamine by different techniques is presented. A 3-mercaptopropyl-functionalized silica network was synthesized using the sol–gel method. Gold nanoparticles (nAu) were immobilized on the material at synthesis by adding a sol of these previously prepared particles to the reaction mixture. The electrochemical behavior of the SiO₂/MPTS/Au carbon paste electrode was studied using cyclic voltammetry in the presence of a hexacyanoferrate probe molecule. The presence of nAu in the functionalized silica network changes the electrochemical characteristics of the material, favoring the electron transfer process of this complex ion. The SiO₂/MPTS/Au electrode was proven to be an efficient tool in the simultaneous determination of ascorbic acid (H₂AA), dopamine (DA), and uric acid (UA) using square wave voltammetry techniques. With the nAu on the electrode, an increase in the peak current related to the redox process of the H₂AA, DA, and UA was observed. The separations of the anodic peak potentials between DA/H₂AA and UA/H₂AA were 310 and 442?mV, respectively. The results obtained show that the SiO₂/MPTS/Au electrode can be used in the simultaneous determination of H₂AA, DA, and UA.     

Detection of Uric Acid in the Presence of Dopamine and High Concentration of Ascorbic Acid Using PDDA Modified Graphite Electrode

The properties of graphite electrode (Gr) modified with poly(diallyl dimethyl ammonium chloride) (PDDA) for the detection of uric acid (UA) in the presence of dopamine (DA) and high concentration of ascorbic acid (AA) have been investigated by cyclic voltammetry, differential pulse voltammetry and chronoamperometry. The polymer modified graphite electrode was prepared by a very simple method just by immersing the graphite electrode in PDDA solution for 20 minutes. The PDDA/Gr modified electrode displayed excellent electrocatalytic activity towards the oxidation of UA, DA and AA compared to that at the bare graphite electrode. The electrochemical oxidation signals of UA, DA and AA are well resolved into three distinct peaks with peak potential separations of 220 mV, 168 mV and 387 mV between AA‐DA, DA‐UA and AA‐UA respectively in cyclic voltammetry studies and the corresponding peak potential separations are 230 mV, 130 mV and 354 mV respectively in differential pulse voltammetry. The lowest detection limits obtained for UA, DA and AA were 1×10^?7 M, 2×10^?7 M and 800×10^?9 M respectively. The PDDA/Gr electrode efficiently eliminated the interference of DA and a high concentration of AA in the determination of UA with good selectivity, sensitivity and reproducibility. The modified electrode was also successfully applied for simultaneous determination of UA, DA and AA in their ternary mixture.     

Structural features of the crystalline iodide complexes of some rare-earth elements with carbamide and acetamide

New acetamide and carbamide complexes LnI₃ · 4Ur · 4H₂O (Ln = La, Eu, Dy, Ho, Y; Ur is carbamide) and LnI₃ · 4AA · 4H₂O (Ln = Nd, Eu, Dy, Ho, Y; AA is acetamide) are synthesized. The complexes are characterized by the data of chemical analysis, IR spectroscopy, and X-ray diffraction analysis. The ligands (water, carbamide, and acetamide molecules) are coordinated by the rare-earth element atoms through the oxygen atom, and the coordination polyhedron is a distorted square antiprism. The iodide ions are not coordinated and are located in the external sphere. The structural characteristics of the complexes are compared in the series [Ln(L)₄(H₂O)₄]I₃ (Ln = La, Nd, Eu, Gd, Dy, Ho, Er; L = AA, Ur).