Electro-deposition of platinum nanoparticles on 4-mercaptobenzene-functionalized multi-walled carbon nanotubes

A new method to electro-deposit platinum nanoparticles on the surface of multi-walled carbon nanotubes (MWNTs) functionalized with 4-mercaptobenzene has been described. X-ray photoelectron spectroscopy results reveal that 4-mercaptobenzene was attached to the surface of MWNTs. Transmission electron microscope and X-ray diffraction analysis confirm that platinum nanoparticles were highly dispersed on the surface of MWNTs, and the average size of the platinum particle is 4.2 nm. The electrocatalytic properties of the Pt/MWNT composite electrode for methanol oxidation were investigated by cyclic voltammetry, and the results show that the fabricated composites exhibit high catalytic activity and good long-term stability. The study provides a feasible approach to fabricate Pt/MWNT composite electrode for direct methanol fuel cell.     

High Dispersion and Electrocatalytic Properties of Platinum on Functional Multi‐Walled Carbon Nanotubes

Platinum (Pt) nanoparticles were electrochemically dispersed on 4‐aminobenzene monolayer‐grafted multi‐walled carbon nanotubes (MWNTs) by a potential‐step method. The structure and nature of the resulting Pt‐MWNT composites were characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The electrocatalytic properties of Pt‐MWNT composites for methanol oxidation have been investigated by cyclic voltammetry (CV) and high electrocatalytic activity can be observed. This may be attributed to the small particle size, high dispersion of platinum particles and the particular properties of MWNT supports. The results imply that the Pt‐MWNT composites have good potential applications in direct methanol fuel cell (DMFC). Additionally, the long‐term cycling stability of platinum catalysts was also investigated.     

Self‐Assembly of Platinum Nanoparticle/Multiwalled Carbon Nanotube Multilayer Film on Au Substrate Electrode

A novel approach to assemble multilayer films of Pt nanoparticle/multiwalled carbon nanotube (MWNTs) composites on Au substrate has been developed for the purpose of improving the methanol oxidation efficiency by providing high catalytic surface area. MWNTs were firstly functionalized with 4‐mercaptobenzene and then assembled on an Au substrate electrode. Pt nanoparticles were fabricated and attached to the surface of the functionalized MWNTs subsequently. Thus a layer of Pt/MWNT composites were assembled on the Au substrate electrode. Repeating above process can assemble different layers of film of Pt/MWNTs composites on the Au electrode. Cyclic voltammetry shows that the Au electrode modified with two layers of film of Pt/MWNT composites exhibits high catalytic ability and long‐term stability for methanol oxidation. The layer‐by‐layer self‐assembly technique provides an efficient strategy to construct complex nanostructure for improving the methanol oxidation efficiency by providing high catalytic surface area.     

碳纳米管尺寸对电化学反应活性的影响

制备不同尺寸的多壁碳纳米管(MWNT)修饰电极,应用循环伏安法研究了相同管径、不同管长和相同管长、不同管径的多壁碳纳米管修饰电极在K3Fe(CN)6溶液中的电化学行为及其对尿酸、多巴胺等生物分子的电催化作用,以及尺寸效应对碳纳米管修饰电极电化学活性的影响规律.结果显示,在同一条件下,短管的MWNT比长管的更能有效促进K3Fe(CN)6的电子传递,更有利于对生物分子的电催化;管径对它的电化学行为及生物电催化活性影响较小,无明显规律.主要原因在于碳纳米管管端、管壁的不同电化学活性.     

Preparation and characterization of multi‐walled carbon nanotubes decorated with silver nanoparticles through ultraviolet irradiation reduction

A facile, green and efficient approach was applied to synthesize multi‐walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (MWNT‐Ag) for further potential application. Oxidized MWNTs were decorated with silver nanoparticles (Ag NPs) via a method combining ultraviolet irradiation‐induced reduction and conventional silver mirror reaction without any reducing agent. The obtained product was characterized using various methods. X‐ray diffraction proved that the Ag NPs were synthesized successfully. Moreover, Ag NPs with a diameter of 80 nm, attached onto MWNTs, could be clearly observed in field emission scanning electron microscopy images, which also confirmed Ag NPs. Energy‐dispersive spectroscopy and transmission electron microscopy also indicated the presence of Ag NPs. Furthermore, thermogravimetric analysis was used to measure the content of Ag NPs in MWNT‐Ag, the result indicating that the weight content of Ag NPs was up to 31.88%. UV–visible absorption spectroscopy was adopted to evaluate the dispersion property of MWNT‐Ag. The result illustrated that MWNT‐Ag had a good dispersibility and stability in water. Characterization was also carried out through Fourier transform infrared spectroscopy, Raman spectroscopy and dynamic light scattering analysis.     

Modification of vertically aligned carbon nanotube arrays with palladium nanoparticles for electrocatalytic reduction of oxygen

A novel type of palladium nanoparticles-modified multiwalled carbon nanotubes composite-electrode with electrocatalytic activity for oxygen reduction is presented. The nanocomposite was prepared by magnetron sputtering deposition with Pd in Ar atmosphere on MWNTs, which were synthesized on Ta plates by chemical vapor deposition. Both scanning electron microscopy and transmission electron microscopy were employed to observe the surface morphology. The Pd nanoparticles, with diameters around 5 nm, are dispersed at the tips and on the sidewalls of the MWNTs. Voltammetry, amperometry and electrochemical impedance measurements were used to demonstrate the strong electrocatalytic activity of the nanocomposite in acid solution. Compared to the bare MWNT electrode, the PdNPs/MWNT nanocomposite shows a positive shift of the O₂ reduction current at onset potentials from +400 to +500 mV, a concurrent 1.5-fold increase in the O₂ reduction peak current with high stability. The successful preparation of PdNPs/MWNTs nanocomposite by magnetron sputtering deposition opens a new path for an efficient dispersion of promising nanoparticles for fuel cells and O₂ sensors.     

Influence of silver-decorated multi-walled carbon nanotubes on electrochemical performance of polyaniline-based electrodes

In this work, silver (Ag) nanoparticles were deposited on multi-walled carbon nanotubes (MWNTs) by chemical reduction while Ag-decorated MWNTs (Ag-MWNTs)/polyaniline (PANI) composites were prepared by oxidation polymerization. The effect of the Ag incorporated into the interface of the composites on the electrochemical performance of the MWNTs/PANI was investigated. It was found that highly dispersed Ag nanoparticles were deposited onto the MWNTs, and the Ag-MWNTs were successfully coated by PANI. According to cyclic voltammograms, the Ag-MWNTs/PANI exhibited significantly increased electrochemical performances compared to MWNTs/PANI and the highest specific capacitance obtained of MWNTs/PANI and 0.15 M Ag-MWNTs/PANI was 162 F/g and 205 F/g, respectively. This indicated that Ag nanoparticles that were deposited onto the MWNTs caused an enhanced electrochemical performance of the MWNTs/PANI due to their high electric conductivity, which resulted in an increase of the charge transfer between the MWNTs and PANI by a bridge effect.     

功能化碳纳米管表面高分散的钯纳米粒子在碱性溶液中的甲醇氧化行为

本工作中在水溶液体系中以芳烃重氮盐修饰的多壁碳纳米管(MWNT)为载体构筑了钯(Pd)纳米粒子碳纳米管复合结构。以MWNT的侧壁上C-C共价键接的氨基苯甲酸为沉积活化中心,制备了高分散高催化活性的钯(Pd)纳米粒子。结构成分和形貌分别用XRD和TEM表征。循环伏安(CV) 和交流阻抗的研究表明上述复合结构在碱性溶液中对甲醇的电催化氧化有很高的活性及稳定性。芳烃重氮盐修饰的MWNT是一种非常好的催化剂载体,而Pd-MWNT复合材料在燃料电池有着广泛的应用前景。     

Crystallization behavior of poly(ε‐caprolactone)/multiwalled carbon nanotube composites

Differential scanning calorimetry (DSC), polarized optical microscopy, and X‐ray diffraction methods were used to investigate the isothermal crystallization behavior and crystalline structure of poly(?‐caprolactone) (PCL)/multiwalled carbon nanotube (MWNT) composites. PCL/MWNT composites were prepared via the mixing of a PCL polymer solution with carboxylic groups containing multiwalled carbon nanotubes (c‐MWNTs). Both Raman and Fourier transform infrared spectra indicated that carboxylic acid groups formed at both ends and on the sidewalls of the MWNTs. A transmission electron microscopy micrograph showed that c‐MWNTs were well separated and uniformly distributed in the PCL matrix. DSC isothermal results revealed that introducing c‐MWNTs into the PCL structure caused strongly heterogeneous nucleation induced by a change in the crystal growth process. The activation energy of PCL drastically decreased with the presence of 0.25 wt % c‐MWNT in PCL/c‐MWNT composites and then increased with increasing MWNT content. The result indicated that the addition of c‐MWNT to PCL induced heterogeneous nucleation (lower total activation energy) at a lower c‐MWNT content and then reduced the transportation ability of polymer chains during crystallization processes at a higher MWNT content (higher total activation energy). A correlation between the crystallization kinetics, melting behavior, and crystalline structure of PCL/c‐MWNT composites was also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 598–606, 2006     

Electrostatic layer-by-layer assembled carbon nanotube multilayer film and its electrocatalytic activity for O2 reduction

Multilayer films of shortened multiwalled carbon nanotubes (MWNTs) are homogeneously and stably assembled on glassy carbon electrodes with the layer-by-layer (LBL) method, based on electrostatic interaction of positively charged poly(diallyldimethylammonium chloride) and negatively charged and shortened MWNTs. The film assembly and electrochemical property as well as the electrocatalytic activity toward O2 reduction of the MWNT multilayer film are studied. Scanning electron microscopy, the quartz crystal microbalance technique, ultraviolet-visible-near-infrared spectroscopy, and cyclic voltammetry are used for characterization of film assembly. Experimental results revealed that film growth is uniform, almost with the same coverage of the MWNTs in each layer, and that the assembled MWNTs are mainly in the form of small bundles or single tubes on the electrodes. Electrochemical studies indicate that the LBL assembled MWNT films possess a remarkable electrocatalytic activity toward O2 reduction in alkaline media. This property, combined with the well-dispersed, porous and conductive features of the MWNT film illustrated with the LBL method, suggests the potential application of the MWNT film for constructing an efficient alkaline air electrode for energy conversions.     

多璧碳管/聚中性红修饰电极的制备及对鸟嘌呤和腺嘌呤的应用研究

结合纳米材料的电催化特性和中性红聚合物薄膜的分子识别能力, 以玻碳电极为基体制备了多壁碳管/聚中性红(MWNT/PNR)修饰电极, 并用表面扫描电镜和循环伏安法进行了表征. 实验表明, 该修饰电极对腺嘌呤(A)和鸟嘌呤(G)都表现出了良好的电催化性能. 在最佳条件下, 用示差脉冲伏安法对A和G进行了测定, 其氧化峰电流于A和G的浓度分别在0.01～4 μmol/L和0.01～8 μmol/L范围内呈良好的线性关系, 检测限均为5×10-9 mol/L (S/N=3). 该修饰电极可以用来同时测定DNA中的A和G.     

The roughened silver–palladium cathode for electrocatalytic reductive dechlorination of 2,4-Dichlorophenoxyacetic acid

The roughened silver–palladium (Pd/Ag(r)) electrode was fabricated by a convenient metallic replacement reaction, and its electrocatalytic property towards reductive dechlorination of 2,4-Dichlorophenoxyacetic acid (2,4-D) in basic aqueous solution have been evaluated. Experimental evidence is presented that Pd/Ag(r) exhibited powerful electrocatalytic activity for dechlorination of 2,4-D. In addition, a new dechlorination mechanism of 2,4-D was proposed, in which the formation of adsorbed 2,4-D on Ag is a key step.     

Electrocatalytic Oxidation of Glucose at Carbon Nanotubes Supported PtRu Nanoparticles and Its Detection

PtRu nanoparticles were supported on multiwall carbon nanotubes (MWNTs), which were further fabricated as an electrode for nonenzymatic glucose sensing. Transmission electron microscope and X‐ray diffraction patterns were used for characterization of the PtRu nanoparticles on MWNTs. Cyclic voltammetry and chronopotentiometry were applied to investigate the performance of the PtRu/MWNTs nanocomposite electrode for nonenzymatic oxidation of glucose. The PtRu/MWNTs electrode shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution and thus can be used to selectively detect glucose. Under the optimal potential (+0.55 V vs. Ag/AgCl), the biosensor effectively performs a selective electrochemical analysis of glucose in the presence of common interferents, such as ascorbic acid (AA), dopamine (DP) and uric acid (UA). Wide linear calibration ranging from 1 mM to 15 mM, high sensitivity of 28.26 μA cm^?2 mM^?1, low detection limit of 2.5×10^?5 M, and fast response time of 10 s were achieved for the detection of glucose at the PtRu/MWNTs electrode.     

Poly(L‐lactide) crystallization induced by multiwall carbon nanotubes at very low loading

Poly(L ‐lactide) (PLLA)/multiwall carbon nanotube (MWNT) composites were prepared by the solvent‐ultrasonic‐casting method. Only very low concentrations of MWNTs (<0.08 wt %) were added in the composites. Isothermal and nonisothermal crystalline measurements were carried out on PLLA/MWNT composites to investigate the effect of MWNTs on PLLA crystalline behavior. DSC results showed that the incorporation of MWNTs significantly shortened the crystalline induction time and increased the final crystallinity of the composite, which indicated MWNTs have a strong nucleation effect on PLLA even at very low concentrations. The nonisothermal crystallization measurements showed that the MWNTs greatly speed up crystallization during cooling. From isothermal crystallization results, both PLLA and PLLA/MWNT composites samples closely followed a relationship based on Lauritzen‐Hoffman theory, with the regime II to III transition shifting to lower temperature with increasing MWNT concentration. A double melting peak appeared in both nonisothermal and isothermal measurements. The conditions under which it appeared were found to closely depend on the regime II‐III transition temperature obtained from Lauritzen‐Hoffman theory. From the magnitude and position of melting peaks, it is proposed that the double melting peak is caused by a disorder‐order crystal phase transition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2341–2352, 2009     

Characterization and electrical properties of polypyrrole/multiwalled carbon nanotube composites synthesized by in situ chemical oxidative polymerization

This study describes the preparation of polypyrrole (PPy)/multiwalled carbon nanotube (MWNT) composites by in situ chemical oxidative polymerization. Various ratios of MWNTs, which served as hard templates, were first dispersed in aqueous solutions with the surfactant cetyltrimethylammonium bromide to form micelle/MWNT templates and overcome the difficulty of MWNTs dispersing into insoluble solutions of pyrrole monomer, and PPy was then synthesized via in situ chemical oxidative polymerization on the surface of the templates. Raman spectroscopy, Fourier transform infrared (FTIR), field‐emission scanning electron microscopy (FESEM), and high‐resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the fabricated composites. Structural analysis using FESEM and HRTEM showed that the PPy/MWNT composites were core (MWNT)–shell (PPy) tubular structures. Raman and FTIR spectra of the composites were almost identical to those of PPy, supporting the idea that MWNTs served as the core in the formation of a coaxial nanostructure for the composites. The conductivities of these PPy/MWNT composites were about 150% higher than those of PPy without MWNTs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1413–1418, 2006     

Myoglobin on multi-walled carbon nanotubes modified electrode: direct electrochemistry and electrocatalysis

Electrochemical behavior of myoglobin (Myb) incorporated on multi-walled carbon nanotubes (MWNTs) modified GC electrode is investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The results indicate that Myb can be strongly adsorbed on the surface of the MWNT-modified electrode to form an approximate monolayer film. MWNTs can greatly promote the redox of horse heart Myb, on which a pair of well-defined and nearly reversible CV peaks for Myb Fe(III)/Fe(II) redox couple were obtained in pH 7.0 buffers. The formal potential of Myb on MWNT modified electrode shifts linearly with pH with a slope of −56.4 mV/pH, showing that the electron transfer is accompanied by single proton transportation. The high efficiency of the Myb/MWNT modified electrode towards the catalytic electro-reduction of nitric oxide has been observed. Potential application of Myb/MWNT modified electrode as biosensors to monitor NO is proposed.     

Direct Electrochemistry of Multi‐Copper Oxidases at Carbon Nanotubes Noncovalently Functionalized with Cellulose Derivatives

This study describes the direct electron transfer of multi‐copper oxidases, i.e., laccase (from Trametes versicolor) and bilirubin oxidase (BOD, from Myrothecium verrucaria) at multiwalled carbon nanotubes (MWNTs) noncovalently functionalized with biopolymers of cellulose derivatives, i.e., hydroxyethyl cellulose (HEC), methyl cellulose (MC), and carboxymethyl cellulose (CMC). The functionalization of the MWNTs with the cellulose derivatives is found to substantially solubilize the MWNTs into aqueous media and to avoid their aggregation on electrode surface. Under anaerobic conditions, the redox properties of laccase and BOD are difficult to be defined with cyclic voltammetry at either laccase/MWNT‐modified or BOD/MWNT‐modified electrodes. The direct electron transfer properties of laccase and BOD are thus studied in terms of the bioelectrocatalytic activities of the laccase/MWNT‐modified and BOD/MWNT‐modified electrodes toward the reduction of oxygen and found to be facilitated at the functionalized MWNTs. The possible application of the laccase‐catalyzed O₂ reduction at the laccase/MWNT‐modified electrode is illustrated by constructing a CNT‐based ascorbate/O₂ biofuel cell with the MWNT‐modified electrode as the anode for the oxidation of ascorbate biofuel.     

Synthesis of Hexagonal Co3O4 and Ag/Co3O4 Composite Nanosheets and their Electrocatalytic Performances

Sheet-like precursors of Co₃O₄ and Ag/Co₃O₄ composites with different Ag contents were synthesized with assistance of triethylamine via a hydrothermal process. The final samples were fabricated by calcing each precursor at 400 °C. The as-prepared samples were identified and characterized by thermogravimetric analysis and differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, and field emission scanning electron microscopy, respectively. The Co₃O₄ and Ag/Co₃O₄ composite samples were used as electrocatalysts modified on a glassy carbon electrode for p-nitrophenol reduction in a basic solution. The electrocatalytic results indicated that all the samples showed enhanced electrocatalytic performance for p-nitrophenol by comparing a bare glass carbon electrode, and p-nitrophenol could be reduced by Co₃O₄ at a high peak current but a rather higher peak potential but be reduced effectively by Ag/Co₃O₄ composites at lower potential. Ag/Co₃O₄ composites with 4 % Ag displayed the highest electrocatalytic activity.     

Preparation,structure, and property of polyoxymethylene/carbon nanotubes thermal conducive composites

Polyoxymethylene (POM)/multiwalled carbon nanotubes (MWNTs) nanocomposites were prepared through a simple solution‐evaporation method assisted by ultrasonic irradiation. To enhance the dispersion of MWNTs in POM, MWNTs were chemically functionalized with PEG‐substituted amine (MWNT‐g‐PEG), which exhibited strong affinity with POM due to their similar molecular structure. The thermal conductivity and the mechanical properties of the composites were investigated, which showed that the thermal conductive properties of POM were improved remarkably in the presence of MWNTs, whereas reduced by using MWNT‐g‐PEG due to the heat transport barrier of the grafted‐PEG‐substituted amine chain. A nonlinear increase of the thermal conductivity was observed with increasing MWNTs content, and the Maxwell‐Eucken model and the Agari model were used for theoretical evaluation. The relatively high effective length factor of the composite predicted with mixture equation indicated that there were few entangles of MWNTs for the samples of MWNT‐g‐PEG in the composites. The mechanical strength of the composites can be improved remarkably by using suitable content of such functionalized MWNTs, and with the increase of the aliphatic chain length of PEG‐substituted amine, the toughness of the composites can be enhanced. Transmission electron microscope result indicated that MWNT‐g‐PEG exhibited strong affinity with POM and a good dispersion of MWNTs was achieved in POM matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 905–912, 2010     

Nonenzymatic electrochemical glucose sensor based on MnO2/MWNTs nanocomposite

In this communication, an amperometric glucose biosensor based on MnO₂/MWNTs electrode was reported. MnO₂ was homogeneously coated on vertically aligned MWNTs by electrodeposition. The MnO₂/MWNTs electrode displayed high electrocatalytic activity towards the oxidation of glucose in alkaline solution, showing about 0.30 V negative shift in peak potential with oxidation starting at ca. −0.20 V (vs. 3 M KCl–Ag/AgCl) as compared with bare MWNTs electrode. At an applied potential of +0.30 V, the MnO₂/MWNTs electrode gives a linear dependence (R = 0.995) in the glucose concentration up to 28 mM with a sensitivity of 33.19 μA mM⁻¹. Meanwhile, the MnO₂/MWNTs electrode is also highly resistant toward poisoning by chloride ions. In addition, interference from the oxidation of common interfering species such as ascorbic acid, dopamine, and uric acid is effectively avoided. The MnO₂/MWNTs electrode allows highly sensitive, low-potential, stable, and fast amperometric sensing of glucose, which is promising for the development of nonenzymatic glucose sensor.