Nanocomposites based on chromium oxide and carbon nanotubes for oxygen electrodes of power cells

Electrochemical method for production of nanostructured composites based on multiple-wall carbon nanotubes and an oxide chromium compound is suggested.     

Electrocatalytic properties of multiwalled carbon nanotubes-based nanocomposites for oxygen electrodes

Metals (platinum, nickel, and lead) and oxides (manganese dioxide and molybdenum, chromium, cobalt, and niobium oxides) were deposited onto multiwalled carbon nanotubes by chemical and electrochemical methods. The resulting nanocomposites were tested as oxygen electrode materials for electrochemical power sources with alkaline electrolytes. A correlation was revealed between the catalytic activity of oxygen electrodes manufactured from composites based on carbon nanotubes with catalyst deposited, on the one hand, and the coefficient a in the Tafel equation for the oxygen evolution reaction on this catalyst, on the other. A possibility of predicting and evaluating the catalytic properties of oxygen electrode materials for power sources was suggested.     

Electrochemical behavior of membranes of ion-selective electrodes based on complex oxides

Lead-selective film electrodes with solid contact with membranes on the basis of niobates and vanadates of compositions Sr_2.75Pb_0.25La(VO₄)₃, Ba_3.8Pb_0.2Nb₂O₉, Ba_3.5Pb_0.5Nb₂O₉, Pb₃NiNb₂O₉, and Pb₂Nb₂O₇ are constructed and studied. Basic electrochemical characteristics of ion-selective electrodes, such as linearity region and steepness of the electrode function, working pH interval, type of electrode function, and reproducibility are determined. The electrode with a membrane on the basis of Pb₃NiNb₂O₉ is tested and recommended as an indicator in the method of potentiostatic titration. The optimum titrant for assaying ions of lead(II) in solution is potassium chromate.     

Solid-state reference electrodes based on carbon nanotubes and polyacrylate membranes

A novel potentiometric solid-state reference electrode containing single-walled carbon nanotubes as the transducer layer between a polyacrylate membrane and the conductor is reported here. Single-walled carbon nanotubes act as an efficient transducer of the constant potentiometric signal originating from the reference membrane containing the Ag/AgCl/Cl⁻ ions system, and they are needed to obtain a stable reference potentiometric signal. Furthermore, we have taken advantage of the light insensitivity of single-walled carbon nanotubes to improve the analytical performance characteristics of previously reported solid-state reference electrodes. Four different polyacrylate polymers have been selected in order to identify the most efficient reservoir for the Ag/AgCl system. Finally, two different arrangements have been assessed: (1) a solid-state reference electrode using photo-polymerised n-butyl acrylate polymer and (2) a thermo-polymerised methyl methacrylate:n-butyl acrylate (1:10) polymer. The sensitivity to various salts, pH and light, as well as time of response and stability, has been tested: the best results were obtained using single-walled carbon nanotubes and photo-polymerised n-butyl acrylate polymer. Water transport plays an important role in the potentiometric performance of acrylate membranes, so a new screening test method has been developed to qualitatively assess the difference in water percolation between the polyacrylic membranes studied. The results presented here open the way for the true miniaturisation of potentiometric systems using the excellent properties of single-walled carbon nanotubes.     

Electrochemical study and flow injection analysis of paracetamol in pharmaceutical formulations based on screen-printed electrodes and carbon nanotubes

Acetaminophenol or paracetamol is one of the most commonly used analgesics in pharmaceutical formulations. Acetaminophen is electroactive and voltammetric mechanistic studies for the electrode processes of the acetaminophenol/N-acetyl-p-quinoneimine redox system are presented. Carbon nanotubes modified screen-printed electrodes with enhanced electron transfer properties are used for the study of the electrochemical-chemical oxidation mechanism of paracetamol at pH 2.0.Quantitative analysis of paracetamol by using its oxidation process (in a Britton-Robinson buffer solution pH 10.0) at +0.20 V (vs. an Ag pseudoreference electrode) on an untreated screen-printed carbon electrode (SPCE) was carried out. Thus, a cyclic voltammetric based reproducible determination of acetaminophen (R.S.D., 2.2%) in the range 2.5 × 10⁻⁶ M to 1 × 10⁻³ M, was obtained. However, when SPCEs are used as amperometric detectors coupled to a flow injection analysis (FIA) system, the detection limit achieved for paracetamol was 1 × 10⁻⁷ M, one order of magnitude lower than that obtained by voltammetric analysis. The repeatability of the amperometric detection with the same SPCE is 2% for 15 successive injections of 10⁻⁵ M acetaminophen and do not present any memory effect.Finally, the applicability of using screen-printed carbon electrodes for the electrochemical detection of paracetamol (i.e. for quality control analysis) was demonstrated by using two commercial pharmaceutical products.     

Preparation of nanocomposites of metals, metal oxides, and carbon nanotubes via self-assembly

Carbon nanotubes (CNTs)-based composites have attracted significant research interest in recent years, owing to their important applications in various technological fields. In this investigation, we describe a general approach to make CNTs-based nanocomposites via self-assembly. The method allows one to prepare binary composites as well as complex systems such as ternary or even quaternary composites where nanoparticles of active phases (e.g., metals and metal oxides) are used as primary building blocks. Six different kinds of binary, ternary, and quaternary nanocomposites, TiO2/CNTs, Co3O4/CNTs, Au/CNTs, Au/TiO2/CNTs, TiO2/Co3O4/CNTs, and Co/CoO/Co3O4/CNTs, have been reported herein in order to draw common features for various assembly schemes. To understand the interconnectivity between the active phases and CNTs, we have devised a range of experiments and examined the resultant samples with many instrumental techniques. On the basis of this work, we demonstrate that highly complex inorganic-organic nanohybrids with good controls in particle shape, size, and distribution can be fabricated from presynthesized nanobuilding units. Concerning their workability, we further show that self-assembled TiO2/CNTs are sufficiently robust and the electrochemical performance of TiO2 is significantly enhanced when it is used as a cathode material in Li-battery application.     

Electrochemical behaviour of oxygen reduction on polymer carbon electrodes in alkaline media

The preparation of polymer carbon electrocatalysts by the controlled pyrolysis of polyfurfuryl alcohol polymer is described. The potentiostatic method was used to study the electrochemical behaviour of the oxygen reduction reaction on the prepared catalyst electrodes in potassium hydroxide electrolyte. A pure polymer carbon electrode and a cobalt chloride doped polymer carbon electrode were shown to be active in oxygen reduction, but the electrode containing cobalt chloride seemed the most active. The main reaction product at the pure polymer electrode is hydrogen peroxide, involving two electrons, whereas at a poly(CoCl₂) electrode the reduction process reaches partly its ultimate state, and involves at most three electrons.     

Electrochemical determination of unithiol and lipoic acid at electrodes modified with carbon nanotubes

Conditions are found for the voltammetric determination of lipoic acid and unithiol at a glassy-carbon electrode modified with multiwalled carbon nanotubes. Possible mechanisms for the oxidation of lipoic acid and unithiol are proposed. As compared to an unmodified electrode, the use of the modified electrode allows the analyst to reduce overvoltage (ΔE = 0.1 V) and increase the oxidation current of lipoic acid. Unithiol is oxidized in the accessible range of potentials only at an electrode modified with carbon nanotubes. The determination limits for unithiol and lipoic acid are 4.1 × 10^?5 and 1.9 × 10^?5 M, respectively. Milligram amounts of these substances are determined in model solutions with RSD = 1–5%. Procedures for determining the active substances (lipoic acid and unithiol) in pharmaceuticals are proposed.     

Electrochemical behavior of some purine derivatives on carbon based electrodes

The electrochemical behaviour of three purine derivatives was investigated by cyclic voltammetry on different electrode materials: glassy carbon in native form and electrochemically activated, carbon paste electrode unmodified or modified with 1, 4-benzoquinone. The preliminary study obtained on solid electrodes was extended to graphite based planar screen-printed electrodes, unmodified and modified with multi-wall carbon nanotubes, or cobalt phthalocyanine.     

Polyethylene thermal oxidative stabilisation in carbon nanotubes based nanocomposites

Multiwall carbon nanotubes (MWNT)/linear low density polyethylene (LLDPE) nanocomposites were studied in order to understand the stabilisation mechanism for their thermal and oxidative degradation. Thermogravimetry coupled with infrared evolved gas analysis and pyrolysis gas chromatography-mass spectrometry demonstrate that MWNT presence slightly delays thermal volatilisation (15-20 °C) without modification of thermal degradation mechanism. Whereas thermal oxidative degradation in air is delayed by about 100 °C independently from MWNT concentration in the range used here (0.5-3.0 wt.%). The stabilisation is due to formation of a thin protective film of MWNT/carbon char composite generated on the surface of the nanocomposites is shown by SEM and ATR FTIR of degradation residues. The film formation mechanism is discussed.     

Polymerization from the surface of single-walled carbon nanotubes - preparation and characterization of nanocomposites

Single-walled carbon nanotubes were functionalized along their sidewalls with phenol groups using the 1,3-dipolar cycloaddition reaction. These phenols could be further derivatized with 2-bromoisobutyryl bromide, resulting in the attachment of atom transfer radical polymerization initiators to the sidewalls of the nanotubes. These initiators were found to be active in the polymerization of methyl methacrylate and tert-butyl acrylate from the surface of the nanotubes. However, the polymerizations were not controlled, leading to the production of high molecular weight polymers with relatively large polydispersities. The resulting polymerized nanotubes were analyzed by IR, Raman spectroscopy, DSC, TEM, and AFM. The nanotubes functionalized with poly(methyl methacrylate) were found to be insoluble, while those functionalized with poly(tert-butyl acrylate) were soluble in a variety of organic solvents. The tert-butyl groups of these appended polymers could also be removed to produce nanotubes functionalized with poly(acrylic acid), resulting in structures that are soluble in aqueous solutions.     

Metallic single-walled carbon nanotubes for conductive nanocomposites

This article reports an unambiguous demonstration that bulk-separated metallic single-walled carbon nanotubes offer superior performance (consistently and substantially better than the as-produced nanotube sample) in conductive composites with poly(3-hexylthiophene) and also in transparent conductive coatings based on PEDOT:PSS. The results serve as a validation on the widely held view that the carbon nanotubes are competitive in various technologies currently dominated by conductive inorganic materials (such as indium tin oxide).     

基于碳纳米管/钯纳米粒子复合材料的电化学传感平台

在碳纳米管存在下合成了直径2~10nm的钯纳米粒子,利用全氟磺酸盐聚合物Nafion溶解碳纳米管/钯纳米粒子复合物,构建了检测H2O2的电化学传感平台.循环伏安法证实所合成的钯纳米粒子在复合材料中保持了其电化学活性,该纳米复合物对H2O2具有催化能力.将葡萄糖氧化酶固定在碳纳米管/钯纳米粒子复合物修饰的玻碳电极上,制备...     

多壁碳纳米管修饰电极上阿替洛尔电化学行为的研究及其测定

基于多壁碳纳米管修饰玻碳电极对阿替洛尔的催化作用,建立了测定阿替洛尔的电化学分析方法。多壁碳纳米管修饰玻碳电极与裸玻碳电极相比,显著提高了阿替洛尔的氧化峰电流,降低了氧化峰电位,提高了测定的灵敏度。该电极测定阿替洛尔的线性范围为4.9×10-6~6.3×10-4mol/L,检出限为2×10-6mol/L。对1.3×10-4mol/L阿替洛尔进行11次平行测定,相对标准偏差为4.4%。此法可用于阿替洛尔片剂中阿替洛尔的测定。     

Electrochemical DNA biosensors based on platinum nanoparticles combined carbon nanotubes

Platinum nanoparticles were used in combination with multi-walled carbon nanotubes (MWCNTs) for fabricating sensitivity-enhanced electrochemical DNA biosensor. Multi-walled carbon nanotubes and platinum nanoparticles were dispersed in Nafion, which were used to fabricate the modification of the glassy carbon electrode (GCE) surface. Oligonucleotides with amino groups at the 5′ end were covalently linked onto carboxylic groups of MWCNTs on the electrode. The hybridization events were monitored by differential pulse voltammetry (DPV) measurement of the intercalated daunomycin. Due to the ability of carbon nanotubes to promote electron-transfer reactions, the high catalytic activities of platinum nanoparticles for chemical reactions, the sensitivity of presented electrochemical DNA biosensors was remarkably improved. The detection limit of the method for target DNA was 1.0 × 10⁻¹¹ mol l⁻¹.     

Electrochemical determination of chromium(VI) using metallic nanoparticle-modified carbon screen-printed electrodes

Carbon screen-printed electrodes (CSPEs) modified with metal nanoparticles present an interesting alternative in the determination of chromium(VI) by differential pulse voltammetry (DPV).Metallic silver and gold nanoparticle deposits have been obtained by electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized silver and gold nanoparticles are deposited in aggregated form.The detection limit for the analytical procedures developed in this work were 8.5 × 10⁻⁷ and 4.0 × 10⁻⁷ M for silver and gold nanoparticle-modifed CSPE, respectively.In terms of reproducibility, the precision of the above-mentioned method was calculated at 6.7% in %R.S.D. values for silver and 3.21% for gold nanoparticle CSPE.     

Electrochemical preparation of luminescent graphene quantum dots from multiwalled carbon nanotubes

Green luminescent, graphene quantum dots (GQDs) with a uniform size of 3, 5, and 8.2(±0.3)?nm in diameter were prepared electrochemically from MWCNTs in propylene carbonate by using LiClO(4) at 90?°C, whereas similar particles of 23(±2)?nm were obtained at 30?°C under identical conditions. Both these sets of GQDs displayed a remarkable quantum efficiency of 6.3 and 5.1?%, respectively. This method offers a novel strategy to synthesise size-tunable GQDs as evidenced by multiple characterisation techniques like transmission and scanning electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction (XRD). Photoluminescence of these GQDs can be tailored by size variation through a systematic change in key process parameters, like diameter of carbon nanotube, electric field, concentration of supporting electrolyte and temperature. GQDs are promising candidates for a variety of applications, such as biomarkers, nanoelectronic devices and chemosensors due to their unique features, like high photostability, biocompatibility, nontoxicity and tunable solubility in water.     

Electrochemical reduction of oxygen on double-walled carbon nanotube modified glassy carbon electrodes in acid and alkaline solutions

The oxygen reduction reaction has been investigated on double-walled carbon nanotube (DWCNT) modified glassy carbon (GC) electrodes in acid and alkaline media using the rotating disk electrode (RDE) method. The surface morphology and composition of DWCNT samples was examined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Aqueous suspensions of DWCNTs were prepared using Nafion and non-ionic surfactant Triton X-100 as dispersing agents. The RDE results indicated that the DWCNT modified GC electrodes are active catalysts for oxygen reduction in alkaline solution. In acid media DWCNT/GC electrodes possess poor electrocatalytic properties for O₂ reduction which indicates lack of metal catalyst impurities in the DWCNT material studied. The oxygen reduction behaviour of DWCNTs was similar to that of multi-walled carbon nanotubes (MWCNTs) observed in our previous studies.     

Electrochemical sensing platform based on the carbon nanotubes/redox mediators-biopolymer system

A new electrochemical sensing platform was developed that relied on synergy between carbon nanotubes (CNT) and redox mediators that were co-immobilized in the biopolymer chitosan (CHIT). To demonstrate the concept, the redox mediator Toluidine Blue O (TBO) and CNT were integrated in CHIT and used for the determination of a reduced form of nicotinamide adenine dinucleotide (NADH). As compared to CHIT-TBO, the CHIT-TBO/CNT films displayed large amplification of a current due to the TBO-mediated oxidation of NADH at -0.10 V. This was discussed in terms of the TBO/CNT synergy that resulted in the improved charge propagation through the CHIT-TBO/CNT matrix.