Investigation of Electrochemical Properties of Carbon Nanofibers Prepared by CCVD Method

Carbon nanofibers, with diameters between 80 and 290 nm and specific area of 242 m²g^-1, have been prepared by the catalytic chemical vapor deposition method. After preparation, the powder was mixed with silicon oil in order to create a paste electrode. The electrochemical behavior of this type of electrode was investigated by cyclic voltammetry, using a solution of 10^-3 M ferrocenecarboxylic acid as mediator. The redox process is quasi-reversible, and it involves the transfer of electrons between Fe(II) and Fe(III).

The same mediator was used for the construction of a second-generation glucose biosensor. The mediator was co-immobilized with the enzyme in the carbon nanofibers paste. The sensor linearly responded to glucose, in the concentration range of 1.7 to 7 mM. A time of around 30 seconds was required to reach 95% of the maximum steady-state current.

Also, the oxidation of calf thymus DNA at the carbon nanofiber paste electrode was investigated by differential pulse voltammetry (DPV). A clear signal, due to guanine oxidation, was obtained in the case of single-stranded DNA.     

A non-enzymatic amperometric sensor for glucose based on cobalt oxide nanoparticles

A cobalt oxide nanoparticle-modified glassy carbon (CONM/GC) electrode was prepared by potential cycling in a pH-controlled solution containing tartrate. The electrocatalytic oxidation of glucose on CONM/GC electrode in alkaline solution was investigated and the kinetics was developed. In cyclic voltammograms, the peak current of the oxidation of low valence cobalt oxide in the presence of glucose is increased and it was followed by a decrease in the corresponding cathodic current. This suggested that glucose oxidation was being catalysed on the redox mediator with an electrocatalytic mechanism. Using cyclic voltammetry, chronoamperometry, steady-state polarisation measurements and impedance spectroscopy, the kinetic parameters of the glucose electrooxidation such as charge-transfer coefficient, the catalytic reaction rate constant and the diffusion coefficient were determined. Based on the results, an efficient enzyme-less sensing procedure for determination of glucose was developed. The resulting sensor exhibited excellent performance for the glucose determination and a sensitive and time-saving amperometric procedure was successfully applied for the quantification of glucose in both batch and flow systems. Glucose was determined with a linear range of 0.7–60?µM, a limit of detection of 0.15?µM and a sensitivity of 2515.35?µA?mM^?1?cm^?2 in batch system and with a linear range of 1.3–50?µM, a limit of detection of 0.14?µM and a sensitivity of 3240.25?µA?mM^?1?cm^?2 in the flow system.     

Coaxial electrospinning fabrication and electrochemical properties of LiFePO4/C/Ag composite hollow nanofibers

LiFePO₄/C/Ag composite hollow nanofibers were synthesized by calcination of the coaxial electrospun nanofibers with polyvinyl pyrrolidone (PVP) as core and [LiOH + Fe(NO₃)₃ + H₃PO₄]/PVP/AgNO₃ as shell. PVP was used as the electrospinning template and carbon source. During the calcination, LiFePO₄ precursor was transformed to LiFePO₄ while AgNO₃ and PVP were decomposed into silver and carbon. The morphology and properties of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, BET specific surface area analysis, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The results indicate that the mean diameter of as-prepared LiFePO₄/C/Ag composite hollow nanofibers is 154.5 ± 18.6 nm and the BET specific surface area is 119.14 m² g^?1. The addition of silver and carbon does not affect the structure of LiFePO₄, but improves its electrochemical performances. At the current density of 0.2 C, the initial discharge capacity of LiFePO₄/C/Ag hollow nanofibers electrode is 138.71 mAh g^?1, which is higher than that of LiFePO₄/C nanofibers electrode. The improved specific capacity may be attributed to increase electrode conductivity after the introduction of silver. The formation mechanism of the LiFePO₄/C/Ag composite hollow nanofibers was also proposed.     

Solution blown aligned carbon nanofiber yarn as supercapacitor electrode

Carbon materials with various microtextures and wide availabilities represent very attractive electrode materials for supercapacitors. In this paper, a modified solution blowing process, using a pair of parallel rods as collector, was reported to fabricate carbon nanofiber yarn (CNFY) with polyacrylonitrile (PAN) as precursor polymer. The morphology and structure of the nanofibers were investigated. The PAN precursor and carbon nanofibers were well-aligned and their average diameter was 280 nm and 187 nm, respectively. The performance of CNFY as supercapacitor electrode was evaluated. The CNFY possessed high conductivity of 608.7 Scm^?1 and mass specific capacitance of 70 Fg^?1 at the current density of 500 mAg^?1, and the reduction of capacitance is 29.14 % of the initial value at the current density range from 0.5 to 8 Ag^?1. The superior performance of the CNFY electrode was attributed to the well-aligned structure and high electrical conductivity which afforded the potential application as a novel electrode for supercapacitors.     

Electrospinning fabrication and electrochemical properties of LiFePO4/C composite nanofibers

LiFePO₄/C composite nanofibers were synthesized by calcination of the [LiOH + Fe(NO₃)₃ + H₃PO₄]/PVP electrospun nanofibers. Polyvinyl pyrrolidone (PVP) was used as the electrospinning template and carbon source. During the calcination [LiOH + Fe(NO₃)₃ + H₃PO₄] were transformed to LiFePO₄ and PVP was decomposed into carbon. The morphology and properties of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area analysis, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The results indicate that the mean diameter of as-prepared LiFePO₄/C composite nanofibers is 179.08 ± 29.66 nm and the BET specific surface area is 66.59 m² g^?1. The addition of carbon does not affect the structure of LiFePO₄, but improves its electrochemical performances. At the current density of 0.2 C, the initial discharge capacity of LiFePO₄/C electrode is 133.6 mAh g^?1 and there is no obvious capacity fading after 100 cycles. The formation mechanism of the LiFePO₄/C composite nanofibers was also proposed.     

Characterization of enzyme immobilized carbon electrode using covalent-entrapment with polypyrrole

ABSTRACT

This study aimed to improve the enzyme immobilization of electrodes to increase electrical power and lifespan using glucose oxidase in a bioanode, laccase in a biocathode, and glucose as a fuel. Both of these enzymes were immobilized on a carbon paper through covalent entrapment. Electrodes were characterized using electrochemical measurements (cyclic voltammetry) and enzymatic biofuel cells. For continuous 16 h, the maximum power density achieved for a hydrophobic electrode was approximately 80 μW/cm² at 0.13 V. For a hydrophilic electrode, the yield was approximately 130 μW/cm² at 0.25 V, which was significantly higher than that for the hydrophobic electrode. The measurements were performed at a working temperature of 37°C with phosphate buffer solution of pH 7 as an electrolyte, and 10 mM glucose was added to the anode as a fuel. The hydrophilic electrode was superior to the hydrophobic electrode because of the covalent entrapment immobilization of glucose oxidase and laccase enzymes in enzymatic biofuel cells.     

Synthesis and lithium storage properties of interconnected fullerene-like carbon nanofibers encapsulated with tin nanoparticles

Interconnected fullerene-like carbon nanofibers encapsulated with tin nanoparticles (Sn@FLCNFs) were synthesized by a facile and scalable electrospinning method using fullerene-like carbon nanoparticles and PVP as carbon sources. SEM and TEM revealed that Sn nanoparticles have been uniformly embedded into the nanofibers. The self-supported Sn@FLCNFs could be directly used as an anode of lithium-ion battery without adding any polymer and binder; it showed a high initial coulombic efficiency. A reversible capacity as high as 846 mA h g^?1 remained after 100 cycles at a current density of 0.2 A g^?1. When the current density was raised to 1 A g^?1, the reversible capacity maintained 656 mA h g^?1 after 300 cycles. The excellent electrochemical performance can be attributed to the formation of the efficient Li-ions diffusion paths and highly conductive cross-linked network in the Sn@FLCNFs electrode, and the interconnected carbon framework can prevent the Sn nanoparticles from pulverization and re-aggregation during cycles.     

MWCNT modified carbon paste electrode for sensitive determination of nicotine

ABSTRACT

A new sensor for the determination of nicotine is proposed based on the reduction of Cu(II)–nicotine complex at MWCNT modified carbon paste electrode. In borate buffer (pH 7.0) the reduction peak of Cu(II)–nicotine complex was observed at ? 0.05 V (versus Ag/AgCl). The increment of peak current obtained by deducting the reduction peak current of the Cu(II)–nicotine complex was rectilinear with nicotine concentration in the range of 0.05–30.0 n g mL^?1, with a detection limit of 0.01 ng/mL^?1. The method was applied for the sensitive quantification of nicotine in real samples with the satisfactory results.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

Synthesis,characterization, and voltammetric hydrogen peroxide sensing on novel monometallic (Ag,Co/MWCNT) and bimetallic (AgCo/MWCNT) alloy nanoparticles

Multiwall carbon nanotube supported (MWCNT) Ag, Co, and Ag-Co alloy nanocatalysts were synthesized at varying metal loadings by borohydride reduction methods without stabilizers to obtain enhanced hydrogen peroxide sensitivity. The resulting materials were characterized employing Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). For electrochemical measurements carried out cyclic voltammetry (CV) and differential pulse voltammetry (DPV), glassy carbon electrode (GCE) was modified with Ag/MWCNT, Co/MWCNT, and Ag-Co/MWCNT alloy nanoparticles. Ag-Co/MWCNT/GCE exhibited the highest performance toward electrochemical oxidation of H₂O₂ in 0.1 M phosphate buffered solution (PBS). Furthermore, the sensitivity and the limit of detection values for Ag-Co/MWCNT/GCE were obtained as 57.14 µA cm^?2 mM^?1and 0.74 µM, respectively. However, the sensitivity values for Ag/MWCNT/GCE, and Co/MWCNT/GCE are 41.66 and 13.88 µA cm^?2 mM^?1, respectively. The LOD values were predicted as 1.84 µM for Ag/MWCNT/GCE and 3.3 µM for Co/MWCNT/GCE.

In addition, the interference experiment indicated that the Ag-Co/MWCNT alloy nanoparticles have good selectivity toward H₂O₂.     

Voltammetric sensor based on carbon paste electrode modified with molecular imprinted polymer for determination of sulfadiazine in milk and human serum

A new sensitive voltammetric sensor for determination of sulfadiazine is described. The developed sensor is based on carbon paste electrode modified with sulfadiazine imprinted polymer (MIP) as a recognition element. For comparison, a non-imprinted polymer (NIP) modified carbon paste electrode was prepared. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods were performed to study the binding event and electrochemical behavior of sulfadiazine at the modified carbon paste electrodes. The determination of sulfadiazine after its extraction onto the electrode surface was carried out by DPV at 0.92 V vs. Ag/AgCl owing to oxidation of sulfadiazine. Under the optimized operational conditions, the peak current obtained at the MIP modified carbon paste electrode was proportional to the sulfadiazine concentration within the range of 2.0 × 10^? 7–1.0 × 10^? 4 mol L^? 1 with a detection limit and sensitivity of 1.4 × 10^? 7 mol L^? 1 and 4.2 × 10⁵ μA L mol^? 1, respectively. The reproducibility of the developed sensor in terms of relative standard deviation was 2.6%. The sensor was successfully applied for determination of sulfadiazine in spiked cow milk and human serum samples with recovery values in the range of 96.7–100.9%.     

Electrochemical analysis of p-nitrophenol in acidic or alkaline medium using silver nanoparticle decorated multi-walled carbon nanotubes

Silver nanoparticle decorated multi-walled carbon nanotubes (Ag/MWCNT) were prepared by a simple chemical plating method. The Ag/MWCNT nanocomposite modified glassy carbon electrode (Ag/MWCNT/GC) was fabricated. Electrochemical behavior of p-nitrophenol at the Ag/MWCNT/GC was studied by cyclic voltammetry. The Ag/MWCNT/GC electrode shows good electrocatalytic activity for the reduction of p-nitrophenol. Voltammetric determination of p-nitrophenol was carried out. Under optimal experimental conditions, the reduction peak current of p-nitrophenol is linearly proportional to its concentration in a range from 3.0 × 10^?6 to 1.2 × 10^?4 mol L^?1 in acidic medium and 3.5 × 10^?5 to 1.4 × 10^?4 mol L^?1 in alkaline medium, respectively.     

Optimization of Conditions for Preparation of Carbon Origin Solid Electrodes Modified with Carbon Nanotubes

A multi-walled carbon nanotubes (MWCNTs) were used for modification of two solid electrode types, glassy carbon electrode (GC), which is widely used for modification in electroanalysis, and, for the first time, paraffin impregnated graphite electrode (PIGE). The optimization of MWCNT/PIGE and MWCNT/GC electrodes was carried out by altering ultrasonication parameters (ultrasonication time, ultrasound generator performance, and dispersing agent). The preparation of modified electrodes was investigated. The most electrochemically sensitive MWCNT/GC electrode was prepared with nanotubes sonicated for 30 min and the most sensitive MWCNT/PIGE for 20 min, both using ethanol/water solution as dispersing agent and 500 W ultrasound generator performance. Both electrodes were successfully used for analysis of lead performed by DC voltammetry. Current responses were measured for the concentration of lead (II) in range from 1 × 10^?5 to 5 × 10^?5 mol dm^?3 for MWCNT/PIGE and also MWCNT/GC electrode.     

Enhanced non-enzymatic glucose sensing of Cu–BTC-derived porous copper@carbon agglomerate

Porous copper@carbon agglomerate (PCCA) is prepared by pyrolysis of Cu₃(BTC)₂·3H₂O (Cu–BTC, BTC = 1,3,5-benzenetricarboxylic acid) in 5% H₂–N₂ mixture atmosphere. The phase and morphology evolution are thoroughly examined by XRD, Raman, BET, TG, XPS, SEM and TEM, respectively. The results show that PCCA is formed at 400 °C and maintains the cubic morphology of the original Cu–BTC crystal. PCCA is composed by round-shaped copper nanoparticles that covered outside by thin layer of carbon. The non-enzymatic glucose sensing properties of PCCA-modified glassy carbon electrode (Cu/GCE) are characterized by cyclic voltammetry. The sensor shows high sensitivity of 614.3 µA mM^?1 to glucose oxidation and negligible responses toward interference from uric acid, ascorbic acid, dopamine and l-cysteine at the level of their physiological concentrations. The sensor also exhibits rapid response (< 6 s), wide linear range (up to 3.33 mM) and low detection limit (0.29 µM at signal/noise ratio (S/N) = 3). Finally, the good stability, reproducibility and repeatability to glucose detection make PCCA a promising catalyst for non-enzymatic glucose sensor.     

Accumulation and trace measurement of paraquat at kaolin-modified carbon paste electrode

The carbon paste electrode modified by kaolin (KCPE) has been utilized for the determination of pesticides with high sensitivity based on their redox behavior. The experiment is performed on the use of cyclic and square wave voltammetry. Experimental conditions were optimized by varying the accumulation time, kaolin loading and measuring solution pH. Square wave voltammetric response showed a linear calibration curve in the range from 3.9 × 10^? 9 to 9 × 10^? 5 mol L^? 1 with a detection limit of 2 × 10^? 10 mol L^? 1 at kaolin-modified carbon paste electrode. As a result, it was found that there was feasibility in the use of kaolin to improve the carbon paste electrode properties.     

Determination of Pb2+ ions by a modified carbon paste electrode based on multi-walled carbon nanotubes (MWCNTs) and nanosilica

A novel carbon paste ion selective electrode for determination of trace amount of lead was prepared. Multi-walled carbon nanotubes (MWCNTs) and nanosilica were used for improvement of a lead carbon paste sensor response. MWCNTs have a good conductivity which helps the transduction of the signal in carbon paste electrode. The electrode composition of 20 wt% paraffin oil, 57% graphite powder, 15% ionophore (thiram), 5% MWCNTs, and 3% nanosilica showed the stable potential response to Pb²⁺ ions with the Nernstian slope of 29.8 (±0.2) mV decade^?1 over a wide linear concentration range of 10^?7–10^?2 mol L^?1. The electrode has fast response time, and long term stability (more than 2 months). The proposed electrode was used to determine the concentration of lead ions in waste water and black tea samples.     

Application of ionic liquid–TiO2 nanoparticle modified carbon paste electrode for the voltammetric determination of benserazide in biological samples

An ionic liquid–TiO₂ nanoparticle modified carbon paste electrode (IL–TiO₂/CPE) was used as a fast and sensitive tool for the investigation of the electrochemical oxidation of benserazide using voltammetry. This modified electrode has been fabricated using hydrophilic ionic liquid (n-hexyl-3-methylimidazolium hexafluoro phosphate) as a binder. The modified electrode offers a considerable improvement in voltammetric sensitivity toward benserazide, compared to the bare electrode. Using differential pulse voltammetry (DPV), the electrocatalytic oxidation peak current of benserazide shows a linear calibration curve in the range of 1.0–600 μmol L^? 1 benserazide. The limit of detection was equal to 0.4 μmol L^? 1. The relative standard deviation (RSD%) for eight successive assays of 10 μmol L^? 1 benserazide was 1.1%. Finally, the proposed method was successfully applied to the determination of benserazide in real samples such as blood serum and urine.     

Electrochemical properties of V2O5/carbon composite electrodes in aqueous solutions

The reaction mechanism of V₂O₅ xerogel and the electrode properties of V₂O₅/carbon composites in an aqueous electrolyte solution were examined to obtain high-performance electrodes for rechargeable proton batteries. Based on the results of the chemical analysis of the electrode, proton intercalation is suggested to be the dominant reaction mechanism. By using the relationship between the capacity and current density of a thin-film electrode consisting of V₂O₅ xerogel, the diffusion coefficient in the V₂O₅ xerogel was determined to be 8 ± 1 × 10^?11 cm² s^?1. The V₂O₅/carbon composite electrode was prepared by drying a homogeneous dispersion of carbon particles in the V₂O₅ sol. The composite electrodes showed a large capacity of 460 mAh g^?1 at a current density of 1 A g^?1 and maintained a relatively large capacity of 160 mAh g^?1 at 100 A g^?1. These properties were attributed to the homogeneous microstructure of the V₂O₅/carbon composites. The V₂O₅/carbon composite electrodes were thus revealed as high-performance electrodes with large capacities and excellent high-rate capabilities.     

Preparation of cerium oxide–MWCNTs nanocomposite bulk modified carbon ceramic electrode: a sensitive sensor for tamoxifen determination in human serum samples

In this study, cerium oxide and multi-walled carbon nanotubes nanocomposite were incorporated into the carbon ceramic electrode (CeO₂–MWCNTs/CCE) as a renewable electrode for the electrocatalytic purposes. To demonstrate capability of the fabricated electrode, determination of tamoxifen as an important anticancer drug with differential pulse voltammetry technique was evaluated in details. Linear range, limit of detection and sensitivity of the developed sensor were found to be 0.2–40 nM, 0.132 nM and 1.478 µA nM^?1 cm^?2, respectively. Ease of production, low cost and high electron transfer rate of the CeO₂–MWCNTs/CCE promises it as a novel electro-analytical tool for determination of important species in real samples.

     

Electrochemical sensor for selective determination of N-acetylcysteine in the presence of folic acid using a modified carbon nanotube paste electrode

In the present paper, a novel benzoylferrocene (BF) modified carbon nanotube paste electrode (BFCNPE) was prepared. The modified electrode was further used for the successful determination of N-acetylcysteine (NAC), and it showed an excellent electrocatalytic oxidation activity toward NAC with a lower overvoltage, pronounced current response, and good sensitivity. Under the optimized experimental conditions, the proposed electrochemical NAC sensor exhibited a linear calibration plot that ranged from 3.0 × 10^? 7 to 7.0 × 10^? 4 M with a detection limit of 9.0 × 10^? 8 M. Also, Square wave voltammetry (SWV) was used for simultaneous determination of NAC and folic acid (FA) at the modified electrode. Finally, the proposed method was applied to the determination of NAC in NAC tablets.