The electrochemical behavior of an enzyme biosensor electrode using an oxyfluorinated pitch-based carbon

A glucose sensor electrode was prepared by thermally treating a pitch-based carbon material. Oxyfluorination was used to modify the surface of the prepared carbon to induce the formation of hydrophilic functional groups. A glucose oxidase enzyme was effectively loaded onto the surface of the oxyfluorinated carbon and was more sensitive in glucose sensing because of the effects of the improved interfacial affinity between the electrode and the glucose oxidase. The introduced hydrophilic functional groups were examined using XPS analysis. In current–voltage measurements, a higher current was observed in the samples prepared with a higher oxygen content. In addition, a clear redox peak was observed in the surface modified samples. These results can be attributed to efficient electrical resistance measurement by easy electron transfer during glucose sensing. An efficient glucose sensor electrode was prepared using pitch-based carbon, which has beneficial electrical properties, and oxyfluorination, which improves the surface interface.     

A sensitive amperometric bromate sensor based on multi-walled carbon nanotubes/phosphomolybdic acid composite film

An amperometric sensor for bromate was developed based on multi-walled carbon nanotubes (MWNTs)/phosphomolybdic acid (PMo₁₂) composite film coated on a pyrolytic graphite (PG) electrode. MWNTs are dispersed in PMo₁₂ aqueous solution through spontaneous and strong chemisorption between carbon and polyoxometalate, which results in a homogeneous MWNTs/PMo₁₂ composite. Due to the unique electronic and electrocatalytic properties of MWNTs and PMo₁₂, the combination of MWNTs and PMo₁₂ results in a remarkable synergistic augmentation on the response current. The bromate sensor based on the PG/MWNTs/PMo₁₂ electrode has excellent characteristics, such as a detection limit of 0.5 μM, a sensitivity of 760.9 μA mM⁻¹ cm⁻², a response time less than 2 s and a linear range from 5 μM to 15 mM.     

In situ diagnosis of chemical species for the growth of carbon nanotubes in microwave plasma-enhanced chemical vapor deposition

A synthesis of multi-wall carbon nanotubes (MWNTs) by microwave plasma-enhanced chemical vapor deposition using CH₄/H₂/NH₃ gases on Ni/Cr-coated glass at low temperature, was investigated by optical emission spectroscopy (OES) and quadrupole mass spectroscopy (MS). It was observed that the MWNTs were grown within a very restrictive range of the gas compositions. Optical emission lines were observed primarily from atomic hydrogen H_α, molecular hydrogen, and CN radicals. The quadrupole mass spectrum also showed the formation of C₂H₂ and HCN. An addition of a small amount of NH₃ resulted in a decrease of C₂H₂, which could be used to estimate amounts of carbon sources present in the plasma for the growth of MWNTs, and increases of CN and H_α radicals acting as etching species of amorphous carbon. These results show that the etching species of amorphous carbon as well as the growth species are necessary and the ratio between two species have to be in appropriate condition for the synthesis of carbon nanotubes at low temperature. The optimum C₂H₂/H_α ratio in the gas mixture for the growth of MWNTs at low temperature was found to be 1:5 in this study.     

Characterization of a carbon composite electrode for an electrochemical immunosensor

A bioactive platform with a carbon composite electrode was developed for rapid detection of Escherichia coli O157:H7. The porous carbon composite electrode was prepared by a sol-gel method with a mixture of graphite powder and tetraethyl orthosilicate/ethanol. Escherichia coli O157:H7 antibodies were physically adsorbed onto the carbon composite electrode. Direct measurements by cyclic voltammetry and electrochemical impedance spectroscopy in the presence of [Fe(CN)₆]^3−/4− as a redox probe showed that the immobilization of antibodies onto the carbon composite electrode surface and the binding of Escherichia coli O157:H7 cells with antibodies systematically increased the electron-transfer resistance. Those results suggest that a sol-gel derived graphite composite electrode might be utilized as a label-free electrochemical immunosensor for diagnosis, biochemical research, food industry, and so on.     

多壁碳纳米管修饰玻碳电极测定药物野黄芩苷

采用超声波处理多壁碳纳米管,配成修饰液后滴涂于玻碳电极表面制作成多壁碳纳米管修饰玻碳电极（MWNTs/GCE）。以循环伏安法研究了野黄芩苷在修饰电极上的电化学行为,建立了一种电化学检测野黄芩苷的新方法。结果表明,在最佳条件下,野黄芩苷在4.0×10-6~1.0×10-4mol.L-1浓度范围内与峰电流呈良好的线性关系,相关系数r=0.9991。方法检出限为8.2×10-7mol.L-1（S/N=3）。连续测定4.0×10-5mol.L-1的野黄芩苷溶液,RSD为1.8%（n=11）。该方法已成功地应用于注射液和片剂中野黄芩苷的测定。     

Electrocatalysis and determination of uracil on polythionine/multiwall carbon nanotubes modified electrode

A new type of poly (thionine)/multiwall carbon nanotube/glassy carbon (PTH/MWNTs/GC) electrode was fabricated by electropolymerization thionine onto the surface of MWNTs modified GC electrode. The properties and behaviors of the modified electrode were characterized by scanning electron microscopy (SEM) and cyclic voltammetry (CV). The results show that the high sensitivity and selectivity are mainly caused by the unique carbon surface of the carbon nanotubes and the catalytic activity of thionine. The modified electrode exhibited excellent electrocatalytic behavior to the oxidation of uracil, and was firstly applied to determinate the concentration of uracil for the differential pulse voltammograms. Under the optimum conditions, linear calibration equation was obtained over the uracil concentration range from 1.0 × 10^?5 to 5.5 × 10^?2M with a correlation coefficient of 0.9978 and a detection limit 2.0 × 10^?7M (based on S/N = 3) was also gained. The good electrocatalytic response of uracil at PTH/MWNTs/GC electrode suggests that the PTH/MWNTs are an excellent platform for electrochemical biosensing. The modified electrode displays excellent repeatability, stability, and high sensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of P(AN‐co‐VA‐co‐DEMA) fibers coated with multiwalled carbon nanotubes by electrostatic interactions

P(AN‐co‐VA‐co‐DEMA) terpolymers were synthesized by aqueous precipitation copolymerization of acrylonitrile (AN), vinyl acetate (VA), and 2‐dimethylamino ethyl methacrylate (DEMA) with an Na₂S₂O₅–NaClO₃ redox initiating system and fibers from these terpolymers were thus prepared by a wet spinning method. Functionalized multiwalled carbon nanotube (F‐MWNT) networks were created on the surface of P(AN‐co‐VA‐co‐DEMA) fibers by a simple dipping method. The morphology and interfacial interactions of the obtained F‐MWNTs‐coated fibers were characterized by scanning electron microscope, Raman spectroscopy, and Fourier transform infrared spectroscopy. The results showed that F‐MWNTs were assembled on the fibers and the density of F‐MWNTs can be controlled by adjusting the F‐MWNTs content in the dipping solution. The assembly process was driven by electrostatic interactions between the negative charges on the nanotube sidewalls and the positive charges of the fibers. The F‐MWNTs‐coated fibers had a good conductivity. The volume resistivity of the fibers coated with 1.18 wt % F‐MWNTs reached 0.27 Ω·cm, while the original mechanical properties were preserved. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42545.     

Surface properties of oxyfluorinated PAN-based carbon fibers

In this study, the oxyfluorination of PAN-based carbon fibers was undertaken at room temperature using fluorine-oxygen mixtures, and the influence of oxyfluorination on properties such as wettability, surface polarity, surface free energy, conductivity and tensile strength was investigated. As the oxyfluorination time increased at a total pressure of 5 kPa, both the fluorine/carbon and oxygen/carbon ratios increased. The contribution of semicovalent C-F bond to F1s spectra is considerably decreased with increasing total pressure from 5 to 80 kPa, and at the same time, the contribution of covalent C-F bond is increased. As the total pressure of fluorine-oxygen mixtures increased, the contact angle of water significantly decreased and again increased to a similar value to that of as-received carbon fiber. A short oxyfluorination of carbon fibers considerably increased the wettability, that is, hydrophilicity.The electrical conductivity of oxyfluorinated carbon fiber is larger than that of the as-received fiber. This is because the surface region of carbon fiber is fluorinated. An increase in the tensile strength of about 18% after oxyfluorination is observed. The increase in tensile strength of oxyfluorinated carbon fibers can be understood as being due to a decrease in the diameter of the fiber.     

基于碳纳米管-离子液体复合电极的双酚A传感器研究

构建了一种基于碳纳米管-离子液体复合电极的双酚A（BPA）传感器。采用循环伏安法和线性扫描伏安法（LSV）研究了双酚A在该修饰电极上的电化学行为,并对实验条件进行了优化。在最佳条件下,BPA的氧化峰电流与其浓度在0.5-100μM范围内有良好的线性关系（r^2=0.9980）,检出限为0.1μM（S/N=3）。此方法能应用于湖水和塑料袋中BPA的测定,回收率在96.20%-105.20%之间。     

Morphology and mechanical and electrical properties of oriented PVA-VGCF and PVA-MWNT composites

The composites poly(vinyl alcohol) (PVA) and vapor growth carbon fiber (VGCFs) and multi wall carbon nanotubes (MWNTs) were prepared by gelation/crystallization from the mixture of dimethyl sulfoxide (DMSO) and water (H₂O). The composite films were elongated to 5-10-fold uniaxially. The mechanical properties of PVA composites were improved significantly by introduction of VGCFs and MWNTs and also by the orientation of fillers. Compared to VGCFs, MWNTs was more effective to improve the electric conductivity of the composites because of its network structure. The change in the electrical conductivity for the PVA/MWNT composites containing 5 wt% MWNT was independent of the draw ratio up to eight-fold indicating no disruption of the network formation. A certain high level of filler content was proved to be necessary for the promotion of both mechanical and electrical properties in oriented composite.     

Determination of the specific capacitance of conducting polymer/nanotubes composite electrodes using different cell configurations

Composite materials containing 20 wt.% of multiwalled carbon nanotubes (MWNTs) and 80 wt.% of chemically formed conducting polymers (ECP) as polyaniline (PANI) and polypyrrole (PPy) have been prepared and used for supercapacitor electrodes. The well conducting properties of MWNTs and their available mesoporosity allow a good charge propagation in the composites. Moreover, due to the good resiliency of MWNTs, an excellent stability of the supercapacitor electrodes is observed. It has been shown that the capacitance values for the composites strongly depend on the cell construction. In the case of three electrode cells, extremely high values can be found from 250 to 1100 F/g, however in the two electrode cell much smaller specific capacitance values of 190 F/g for PPy/MWNTs and 360 F/g for PANI/MWNTs have been measured. It highlights the fact that only two-electrode cells allow a good estimation of materials performance in electrochemical capacitors. The applied voltage was found to be the key factor influencing the specific capacitance of nanocomposites. For operating each electrode in its optimal potential range, asymmetric capacitors have been built with PPy/MWNTs as negative and PANI/MWNTs as positive electrodes giving capacitance values of 320 F/g per electrode material.     

The effect of electrolytic oxidation on the electrochemical properties of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWNTs) were electrochemically oxidized by a constant-potential electrolysis method and then investigated in detail using scanning electron microscope, transmission electron microscope, FT-IR, electrical impedance spectroscopy, and cyclic voltammetry. The FT-IR spectra showed that the amount of hydroxyl generated on the surface of MWNTs increased with increasing the electrochemical oxidation time of MWNTs. The CV results, being conducted in nitrobenzene solution, showed that the nitrobenzene reduction current increased with the increase in oxidation time of the MWNTs within the first 60 min of electrolysis. An electrical equivalent circuit model for electrical impedance spectroscopy was further established to analyze the surface capacitance and resistance of the MWNTs, and the model results showed that the capacitance of the oxidized MWNTs increased greatly while the charge transfer resistance decreased, suggesting electrochemical oxidized MWNTs modified pyrolytic carbon electrode being an effective electrochemical sensor for nitrobenzene determination.     

Effective electrochemically controlled process for perchlorate removal using poly(aniline‐co‐o‐aminophenol)/multiwalled carbon nanotubes

The study on perchlorate removal from simulated wastewater was carried out using a conducting copolymer poly(aniline‐co‐o‐aminophenol) (PANOA) polymerized on multiwalled carbon nanotubes (MWNTs)‐modified glassy carbon (GC) electrode. The cyclic voltammograms demonstrated that the PANOA/MWNTs GC electrode in a NaCl solution containing NaClO₄ had a good redox activity, reversibility, and stability in a wide range of pHs tested (from pH <1 to 9.0). The ratio of ClO/Cl^? in PANOA/MWNTs was up to 80.8%, which was 10.0% in the solution, indicating that PANOA/MWNTs had a relatively high affinity to perchlorate. The result of X‐ray photoelectron spectroscopy revealed a fact that Cl^? ions can be strongly adsorbed on MWNTs, which resulted in an improvement in the electrical activity of PANOA and perchlorate removal. Therefore, it is possible to develop a green process for removing perchlorate from wastewater using PANOA/MWNTs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Direct Oxyfluorination of Hydrocarbons on Metal Fluorides

A critical overview of the recent literature data and of our results on the oxyfluorination of C–H to C–F bond with metal fluorides is presented. Some important aspects that require further investigation, in order to obtain a better understanding of the reaction mechanism and to develop a general approach to catalysts design are discussed. In particular, the oxyfluorination of ethene, utilizing different metal fluorides, in pulse and continuous reactors, was studied. Obtained results indicated that the presence of mixed fluorides with a fluoroperovskite structure, such as AgCuF₃, led to improved reactant conversion and higher selectivity to vinyl fluoride, in comparison to the single metal fluorides. CO₂ is formed from secondary parallel reaction upon ethene oxidation, because of the presence of metal oxides in the catalysts. The difficulties met in the regeneration of the Ag° formed during oxyfluorination, addressed the search for new metal fluorides as starting materials for the synthesis of perovskite-like materials. Still, among the prepared mixtures only in the case of AgCuF₃ the formation of perovskite-like materials was evidenced by means of XRD; such behaviour is explained by means of the Goldschmidt factor t.     

A novel material based on cupric(II) oxide/macroporous carbon and its enhanced electrochemical property

A novel material based on cupric(II) oxide/macroporous carbon nanocomposites (CuO/MPC) has been prepared through a simple hydrothermal process. In the process of synthesis, the incorporation of MPC leads to a well-dispersed CuO nanoneedles on the surface of MPC. The new composite material combined the unique property of CuO and MPC, showed improved electrochemical activity towards H₂O₂ reduction and glucose oxidation. Based on the improved electrochemical property of CuO/MPC modified electrode, it can be used as sensor for the determination of H₂O₂ and glucose. In addition, the CuO/MPC modified electrode displayed good stability and antifouling features towards glucose oxidation. These results also indicate that CuO/MPC nanocomposites have of wide application foreground.     

Modified glassy carbon electrode with Nafion/MWNTs as a sensitive voltammetric sensor for the determination of paeonol in pharmaceutical and biological samples

A simple, highly sensitive method was reported for directly voltammetric determination of paeonol in drug samples and human biological samples. Nafion/multi-wall carbon nanotubes’ (MWNTs) composite film was coated on the glassy carbon electrode. The adsorptive voltammetric behavior of paeonol on the Nafion/MWNTs-modified electrode was investigated using cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). The results indicated that the Nafion/MWNTs-modified electrode could remarkably enhance electrocatalytic activity toward the oxidation of paeonol, and showed an excellent resistance capability toward the electrode passivation. A highly sensitive voltammetric sensor was developed for the detection of paeonol in pharmaceutical and biological samples. Under the optimum conditions, the anodic peak current was proportional to paeonol concentration in the range of 6.0 × 10⁻⁷–6.0 × 10⁻⁵ M with a detection limit of 4.0 × 10⁻⁷ M. Some kinetic parameters were determined, and multi-step mechanism for oxidation of paeonol was proposed.     

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.     

Fe2+掺杂秸秆黑炭电极的制备及对水中Zn2+的吸附

将玉米秸秆无氧炭化,以葡萄糖为粘合剂掺杂Fe2+水热制备秸秆炭电极,表征了其结构和形貌,考察了电压、时间、pH值对Fe2+炭化电极吸附模拟废水中Zn2+的影响. 结果表明,玉米秸秆与FeSO4×7H2O按质量比1:1所制电极疏松多孔、鼓泡均匀. 在电压14 V、pH值8.0、吸附150 min的条件下,对Zn2+的去除率达88.2%.     

Synthesis of nano-phase ZrC by carbothermal reduction using a ZrO2–carbon nano-composite

Carbothermal reduction of Zr-sucrose gels powders into nano-phase ZrC, or ZrC-Zr(C,O) core-shell powders, via a composite of 2–4 nm sized ZrO₂ and amorphous carbon, is described. Samples with 1.7–20 sucrose-carbon:Zr ratio gels heated to 1495 °C at 10 °Cmin^?1, with 3 and 30 min hold time were studied in detail using; TG, XRD, SEM, TEM, STEM-EDX, and XPS with Ar⁺-ion etching. After 1495 °C, 3 min, the samples with 12-20C:Zr ratios yielded weakly agglomerated 30 to 40 nm sized ZrC particles, surrounded by a dense 5 nm thick shell of Zr(C,O). With 5C:Zr significant amounts of ZrO₂ was present after heating at 1495 °C for 3 min, while after 30 min annealing, ZrC particles without residual amorphous carbon was obtained. Minor amounts of zirconia was found in most samples, which in similarity with the 5 nm Zr(C,O) shell, is believed to stem from post synthesis oxidation.     

Electrochemical poly(1,3-phenylenediamine) synthesis as enzyme immobilization media

Electrochemical polymerization of the 1,3-phenylenediamine in the presence of glucose oxidase with KCl aqueous electrolyte at a potential of 0.800 V versus Ag–AgCl produces adherent poly(1,3-phenylenediamine) containing enzyme (glucose oxidase) film on a platinum electrode. Polymeric sensor prepared in this one-step procedure can be used to determine hydrogen peroxide formed as the result of the enzymatic reaction between glucose and glucose oxidase in the presence of O₂. The amperometric responses of the resultant enzyme electrode to glucose were rapid, reaching steady-state values within 4–5 s, and there was a linear relationship between glucose concentration and obtained current up to 6 mM. Polymeric sensor was stable for more 3 months. The glucose selectivity of enzyme electrode was determined in the presence of some interfering substances, such as lactose, sucrose, urea, uric acid, paracetamol, and ascorbic acid. Also, the effects of buffer concentration, storage conditions, and temperature on the steady-state amperometric responses were studied. Moreover, the Arrhenius activation energy for the enzymatic reaction was calculated. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:145–152, 1998