Understanding the Physicoelectrochemical Properties of Carbon Nanotubes: Current State of the Art

Carbon nanotubes receive considerable attention in the area of electrochemistry not only due to their reported structural, mechanical or electronic properties but because they represent the world's smallest electrodes allowing electrochemistry to be performed where other electrode materials cannot penetrate. In this review, we overview recent developments in this area summarizing the fundamental advances in understanding the various factors and parameters that can significantly affect the electrochemical reactivity of carbon nanotubes, which is essential for their continual use and successful implementation in a plethora of areas and applications.     

Electrochemical Investigations of the Anticancer Drug Idarubicin Using Multiwalled Carbon Nanotubes Modified Glassy Carbon and Pyrolytic Graphite Electrodes

The effect of surface modifications on the electrochemical behavior of the anticancer drug idarubicin was studied at multiwalled carbon nanotubes modified glassy carbon and edge plane pyrolytic graphite electrodes. The surface morphology of the modified electrodes was characterized by scanning electron microscopy. The modified electrodes were constructed for the determination of idarubicin using adsorptive stripping differential pulse voltammetry. The experimental parameters such as supporting electrolyte, pH, accumulation time and potential, amount of carbon nanotubes for the sensitive assay of idarubicin were studied as details. Under the optimized conditions, idarubicin gave a linear response in the range 9.36×10^?8–1.87×10^?6 M for modified glassy carbon and 9.36×10^?8–9.36×10^?7 M for modified edge plane pyrolytic graphite electrodes. The detection limits were found as 1.87×10^?8 M and 3.75×10^?8 M based on modified glassy carbon and edge plane pyrolytic graphite electrodes, respectively. Interfering species such as ascorbic acid, dopamine, and aspirin showed no interference with the selective determination of idarubicin. The analyzing method was fully validated and successfully applied for the determination of idarubicin in its pharmaceutical dosage form. The possible oxidation mechanism of idarubicin was also discussed. The results revealed that the modified electrodes showed an obvious electrocatalytic activity toward the oxidation of idarubicin by a remarkable enhancement in the current response compared with bare electrodes.     

Electrochemical Sensors Based on Carbon Nanotubes

Carbon nanotubes are attractive new materials. It has been about a decade since carbon nanotubes were discovered. Carbon nanotubes have many outstanding properties and have many practical or potential applications. In this short review we introduce recent advances in carbon nanotubes as potential material for electrochemical sensors. The advantages of carbon nanotubes as sensors are discussed along with future prospects.     

基于碳纳米管的化学修饰电极及电化学生物传感器的研究进展

综述了碳纳米管的结构、合成、纯化、功能化、分散及基于碳纳米管的化学修饰电极和电化学生物传感器的研究进展。     

碳纳米管的电化学贮氢性能研究

研究了碳纳米管电极的电化学性能 ,其电化学储氢量达到 2 0 0mAh·g 1且具有高的电化学活性和良好的循环寿命 .采用循环伏安法研究了氢在碳纳米管电极上吸附 /氧化机理 .     

Exploration of Stable Sonoelectrocatalysis for the Electrochemical Reduction of Oxygen

A series of modified electrodes were prepared both via solvent evaporation and electrochemical cycling of azobenzene and derivatives and various quinones and assessed for their suitability as oxygen reduction electrocatalysts and sonoelectrocatalysts. Glassy carbon electrodes were modified via solvent evaporation with 1,2‐dihydroxyanthraquinone and 1,2‐diazonium‐9,10‐anthraquinone while edge plane and basal plane pyrolytic graphite electrodes were modified by the same procedure with 9,10‐phenanthraquinone. The stability of the attached moiety was accessed in each case under ultrasound. For comparison the same electrode substrates were modified with 9,10‐phenanthraquinone by electrochemical cycling and also exposed to ultrasound. The observed results suggest the use of the glassy carbon electrodes modified with azobenzene and derivatives via solvent evaporation as the optimal carbon based sonoelectrocatalysts for oxygen reduction in term of stability under insonation and high catalytic rate.     

The Electrocatalytic Properties of Arc‐MWCNTs and Associated ‘Carbon Onions’

For the first time we report on the electrochemical characteristics of nanometer sized polyhedral graphite onions dispersed amongst arc‐MWCNTs. These are formed during the electric arc discharge method of producing ultrapure MWCNTs (arc‐MWCNTs). The carbon onions are randomly dispersed amongst the arc‐MWCNTs which are produced with very little amorphous carbon deposits or other unwanted impurities and are formed as closed‐ended tubes. By comparison with commercially available open‐ended hollow‐tube multiwalled carbon nanotubes made using the chemical vapor deposition method (cvd‐MWCNTs), a glassy carbon electrode (GCE), an edge‐plane pyrolytic graphite electrode (eppg) and basal plane pyrolytic graphite (bppg) electrode, we can speculate that it is the edge‐plane‐like defect sites that are the electroactive sites responsible for the apparent ‘electrocatalysis’ seen with a wide range of analytes including: ferrocyanide, ruthenium hexaamine(III), nicotinamide adenosine dinucleotide (NADH), epinephrine, norepinephrine, cysteine, and glutathione. The arc‐MWCNTs themselves are produced as closed‐ended tubes with very few, if any, edge‐plane‐like defect sites evident in their HRTEM characterization. Therefore we speculate that it is the carbon onions dispersed amongst the arc‐MWCNTs which have incomplete graphite shells or a rolled‐up ‘Swiss‐roll’ structures that posses the edge‐plane‐like defect sites and are responsible for the observed voltammetric responses. Carbon onions are no more or no less ‘electrocatalytic’ than open‐ended MWCNTs which in turn are no more electrocatalytic than an eppg electrode. As the carbon onions are ubiquitous in MWCNTs formed using the arc‐discharge method the authors advise that caution should be taken before assigning any electrocatalytic behavior to the MWCNTs themselves as any observed electrocatalysis likely arises from the carbon onion impurities.     

Electrocatalytic Properties and Sensor Applications of Fullerenes and Carbon Nanotubes

The electrochemical behavior of fullerene and fullerene derivatives are reviewed with special reference to their catalytic and sensor applications. Recent work on carbon nanotubes, used as catalyst supports in heterogeneous catalysis and sensor development is also presented. An overview of recent progress in the area of fullerene electrochemistry is included. Several cases of electrocatalytic dehalogenation of alkyl halides, assisted by the electrode charge transfer to fullerenes, are discussed. Research work on the electrocatalysis of biomolecules, such as hemin, cytochrome c, DNA, coenzymes, glucose, ascorbic acid, dopamine, etc. have also been considered. Based on the studies of the interaction of fullerenes, fullerene derivatives, and carbon nanotubes with other molecules and biomolecules in particular, the possibilities for the preparation of electrochemical sensors and their application in electroanalytical chemistry are highlighted.     

Comparison of the Electrochemical Reactivity of Carbon Nanotubes Paste Electrodes with Different Types of Multiwalled Carbon Nanotubes

Carbon nanotubes (CNTs) are widely used in electrochemical studies. It is reported that CNTs with different source and dispersed in different agents [1] yield significant difference of electrochemical reactivity. Here we report on the electrochemical performance of CNTs paste electrodes (CNTPEs) prepared by multiwalled carbon nanotubes (MWNTs) with different diameters, lengths and functional groups. The resulting electrodes exhibit remarkable different electrochemical reactivity towards redox molecules such as NADH and K₃[Fe(CN)₆]. It is found that CNTPEs prepared by MWNTs with 20–30 nm diameter show highest catalysis to NADH oxidation, while CNTPEs prepared by MWNTs with carboxylate groups have best electron‐transfer rate (The peak‐peak separation (ΔE_p) is +0.108 V for MWNTs with carboxylate groups, +0.155 V for normal MWNTs, and +0.174 V for short MWNTs) but weak catalysis towards oxidation of NADH owing to the hydrophilicity of carboxylate groups. The electrochemical reactivity depends on the lengths of CNTs to some extent. The ‘long’ CNTs perform better in our study (The oxidation signals of NADH appear below +0.39 V for ‘long’ CNTs and above +0.46 V for the ‘short’ one totally). Readers may get some directions from this article while choose CNTs for electrochemical study.     

Glassy Carbon Electrodes Modified with Multiwall Carbon Nanotubes Dispersed in Polylysine

We report the analytical performance of glassy carbon electrodes (GCE) modified with a dispersion of multiwall carbon nanotubes (MWCNT) in polylysine (Plys) (GCE/MWCNT‐Plys). The resulting electrodes show an excellent electrocatalytic activity towards different bioanalytes like ascorbic acid, uric acid and hydrogen peroxide, with important decrease in their oxidation overvoltages. The dispersion of 1.0 mg/mL MWCNT in 1.0 mg/mL polylysine is highly stable, since after 2 weeks the sensitivity for hydrogen peroxide at GCE modified with this dispersion remained in a 90% of the original value. The MWCNT‐Plys layer immobilized on glassy carbon electrodes has been also used as a platform to build supramolecular architectures by self‐assembling of polyelectrolytes based on the polycationic nature of the polylysine used to disperse the nanotubes. The self‐assembling of glucose oxidase has allowed us to obtain a supramolecular multistructure for glucose biosensing. The influence of glucose oxidase concentration and adsorption time as well as the effect of using polylysine or MWCNT‐Plys as polycationic layers for further adsorption of GOx is also evaluated.     

Preparation and Characterization of Electrodes Modified with Pyrrole Surfactant,Multiwalled Carbon Nanotubes and Metallophthalocyanines for the Electrochemical Detection of Thiols

Our aim was to prepare hybrid electrodes active towards the electrooxidation of thiols by the co‐immobilization of native carbon nanotubes (CNTs) and cobalt phthalocyanine (CoPc) from aqueous solutions. This strategy was adopted to avoid the oxidation of CNTs that can induce a modification of their exceptional properties. To do so, a hydrosoluble pyrrole surfactant was used to get homogeneous aqueous dispersions of CNTs and CoPc and to trap both materials on the electrode via the electropolymerization of the pyrrole surfactant. The hybrid electrodes exhibit a good electrocatalytic activity towards the oxidation of L ‐cysteine and glutathione. Their performances in terms of limit of detection (0.01 mM) are compatible with the detection of these thiols in biological samples.     

Catalytic Induced Thermal Conversion of Amorphous Carbon into Single Walled Carbon Nanotubes

Single walled carbon nanotubes (SWNTs) have caught extensive attention in the field of material science and electronics. Their formation typically uses plasma arc or CVD techniques [1–3]. So far, formation of SWCNTs just by thermal conversion of amorphous, non graphitic carbon which is a nearly ubiquitous carbon source is challenging but has not been reported so far. We herein demonstrate the catalytic growth of SWNTs from an amorphous carbon source (activated charcoal powder, ‘Aktivkohle’) mediated by three different catalytically active metals; metallic nickel, nickel derived from bis(η⁵‐cyclopentadienyl)nickel (nickelocene) and yttrium formed in situ from yttrium oxide.     

Native and denatured forms of proteins can be discriminated at edge plane carbon electrodes

In an attempt to develop a label-free electrochemical method for detection of changes in protein structures based on oxidizability of tyrosine and tryptophan residues we tested different types of carbon electrodes. We found that using edge plane pyrolytic graphite electrode (EPGE) we can discriminate between native and denatured forms of human serum albumin (HSA) and of other proteins, such as bovine and chicken serum albumin, aldolase and concanavalin. Treatment of natively unfolded α-synuclein with 8 M urea resulted only in a small change in the tyrosine oxidation peak, in a good agreement with absence of highly ordered structure in this protein. Using square wave voltammetry with EPGE we were able to follow the course of HSA denaturation at different urea concentrations. The electrochemical denaturation curve agreed reasonably well with that based on intrinsic fluorescence of tyrosine and tryptophan. It can be expected that the electrochemical method will be applicable to a large number of proteins and may become useful in biomedicine and proteomics.     

In Situ Fabrication of Noble Metal Nanoparticles Modified Multiwalled Carbon Nanotubes and Related Electrocatalysis

Using multiwalled carbon nanotubes (MWNTs) as templates, noble metal (Au, Ag, Pt or Pd) nanoparticles (NPs) were fabricated in situ by electrochemistry with a diameter of 40–60 nm. Further, catalytic behaviors of these composite materials were investigated. Experiments showed that such carbon nanotubes decorated with Pd NPs modified glassy carbon electrodes exhibited higher electrocatalytic ability to some molecules such as evolution of hydrogen, reduction of oxygen and oxidation of ascorbic acid. Atomic force microscopy, X‐ray photoelectron spectroscopy and cyclic voltammetry were used to characterize the film formation and their properties.     

Multiwalled Carbon Nanotubes Encased in Ruthenium Oxide Film as a Hybrid Material for Neurotransmitters Sensor

A hybrid film (MWCNTs‐RuO_x?nH₂O) which contains multiwalled carbon nanotubes (MWCNTs) along with the incorporation of ruthenium oxide (RuO_x?nH₂O) has been synthesized on glassy carbon electrode (GCE), gold (Au), indium tin oxide (ITO) and screen printed carbon electrode (SPCE) by potentiostatic methods. The presence of MWCNTs in the hybrid film enhances surface coverage concentration (Γ) of RuO_x?nH₂O to ≈2100%. The surface morphology of the hybrid film deposited on ITO has been studied using scanning electron microscopy and atomic force microscopy. These two techniques reveal that the RuO_x?nH₂O incorporated on MWCNTs. Electrochemical quartz crystal microbalance study too reveals the incorporation of MWCNTs and RuO_x?nH₂O. The MWCNTs‐RuO_x?nH₂O hybrid film exhibits promising enhanced electrocatalytic activity towards the biochemical compounds such as epinephrine and norepinephrine. The electrocatalytic responses of these analytes at RuO_x?nH₂O, MWCNTs and MWCNTs‐RuO_x?nH₂O hybrid films have been measured using cyclic voltammetry. The obtained sensitivity values from electrocatalysis studies of analytes for MWCNTs‐RuO_x?nH₂O hybrid film are higher than the RuO_x?nH₂O and MWCNTs films. Finally, the flow injection analysis has been used for the amperometric studies of analytes at MWCNTs‐RuO_x?nH₂O hybrid film modified SPCEs.     

Understanding the Electrochemical Reactivity of Bamboo Multiwalled Carbon Nanotubes: the Presence of Oxygenated Species at Tube Ends May not Increase Electron Transfer Kinetics

The result of acid washing multiwalled carbon bamboo nanotubes is explored with voltammetry and X‐ray Photoelectron Spectroscopy; it is found that the presence of oxygenated species formed as a result at the ends of the nanotubes does not measurably change the heterogeneous charge transfer kinetics.     

Analytical Potentialities of Carbon Nanotube/Silicone Rubber Composite Electrodes: Determination of Propranolol

A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone‐rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70 % (m/m) electrodes with linear dynamic ranges up to 7.0 µmol L^?1 by differential pulse and up to 5.4 µmol L^?1 by square wave voltammetry, with LODs of 0.12 and 0.078 µmol L^?1, respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.     

Simultaneous Determination of Uric Acid and Ascorbic Acid Using Edge Plane Pyrolytic Graphite Electrodes

Edge plane pyrolytic graphite electrodes have been applied for the determination of uric acid and ascorbic acid. The separate determination of uric acid was found to produce three linear ranges from 100 nM to 3400 μM with a detection limit of 30 nM found to be possible. Uric acid detection was also explored in the presence of 200 μM ascorbic acid where a detection limit of 52 nM was found to be possible. The detection of ascorbic acid in the presence of uric acid was also explored over three linear ranges of ascorbic acid with a limit of detection of 80 nM. Last the simultaneous determination of both uric acid and ascorbic acid is investigated over the range 100 nM to 1000 μM where detection limits of 50 nM and 120 nM were obtained respectively. Analysis of uric acid in a growth tissue medium was found to be successful, confirming the applicability of the methodology to real matrices. This protocol is shown to provide low detection limits, easy handling (no electrode modification), good voltammetric peak separation of uric acid and ascorbic acid and a wide linear dynamic range.     

Direct Oxidation of Ascorbic Acid at an Edge Plane Pyrolytic Graphite Electrode: A Comparison of the Electroanalytical Response with Other Carbon Electrodes

The direct electrochemical oxidation of ascorbic acid at an edge plane pyrolytic graphite electrode (EPPG) is investigated and compared with other common carbon‐based electrodes, specifically glassy carbon, boron doped diamond and basal plane pyrolytic graphite. It is found that the EPPG electrode shows a significantly higher degree of electrochemical reversibility than the other electrode substrates giving rise to an analytically optimized limit of detection and sensitivity of 7.1×10^?5 M and 0.065 A M^?1 respectively.