Preparation of carbon nanotubes supported platinum nanoparticles by an organic colloidal process for nonenzymatic glucose sensing

Multi-walled carbon nanotubes (MWNTs) supported platinum nanoparticles with narrow size distribution were prepared by an organic colloidal process with sodium citrate as the coordination reagent and stabilizer, and ethylene glycol as the reduction reagent. A nonenzymatic glucose sensor with high sensitivity based on the Pt/MWNTs electrode was demonstrated. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to investigate the size distributions and the crystal structure of Pt nanoparticles on the MWNTs. The TEM images show that the Pt nanoparticles with about 2–4 nm in diameter are well dispersed on the MWNTs. The Pt/MWNTs shows high electrocatalytic activity towards the oxidation of glucose in 0.1 M NaOH solution. At +0.5 V, the Pt/MWNTs nanocomposite electrode exhibits linearity in the range of 1 mM to 23 mM (R > 0.998) glucose with a response time of 11.6 s. The detection limit is 50 μM (S/N = 3). It was demonstrated that the Pt/MWNTs electrode with high electrocatalytic activity to glucose oxidation could find application in nonenzymatic detection of glucose.     

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.     

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.     

Electrodeposition of Platinum Nanoparticles on Multi-Walled Carbon Nanotubes for Electrocatalytic Oxidation of Methanol

Platinum (Pt) nanoparticles were deposited at the surface of well-aligned multi-walled carbon nanotubes (MWNTs) by potential cycling between +0.50 and −0.70 V at a scanning rate of 50 mV · s⁻¹ in 5 mM Na₂PtCl₆ solution containing 0.1 M NaCl. The electrocatalytic oxidation of methanol at the nanocomposites of Pt nanoparticles/nanotubes (Pt_nano/MWNTs) has been investigated using 0.2 M H₂SO₄ as supporting electrolyte. The effects of various parameters, such as Pt loading, concentration of methanol, medium temperature as well as the stability of Pt_nano/MWNTs electrode, have been studied. Compared to glassy carbon electrode, carbon nanotube electrode significantly enhances the catalytic efficiency of Pt nanoparticles for methanol oxidation. This improvement in performance is due not only to the high surface area and the fast electron transfer rate of nanotubes but also to the highly dispersed Pt nanoparticles as electrocatalysts at the tips and the sidewalls of nanotubes.     

Preparation of hybrid thin film modified carbon nanotubes on glassy carbon electrode and its electrocatalysis for oxygen reduction

A hybrid thin film containing Pt nanoparticles and [tetrakis(N-methylpyridyl)porphyrinato]cobalt (CoTMPyP) modified multi-walled carbon nanotubes (MWNTs) on a glassy carbon (GC) electrode surface was fabricated. This hybrid film electrode exhibited remarkable electrocatalytic activity for oxygen reduction and high stability with promising applications in fuel cells.     

Nanocomposite based on depositing platinum nanostructure onto carbon nanotubes through a one-pot, facile synthesis method for amperometric sensing

Platinum nanoparticles (Pt NPs) were deposited onto multi-walled carbon nanotubes (MWNTs) through direct chemical reduction without any other stabilizing agents. Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry were employed to characterize the morphology of the as-prepared nanocomposite (noted as Pt NPs-MWNTs) and further identify the Pt NPs on the surface of MWNTs. The nanocomposite demonstrated the ability to electrocatalyze the oxidation of hydrogen peroxide and substantially raises the response current. A sensitivity of 591.33 μA mM⁻¹ cm⁻² was obtained at Pt NPs-MWNTs modified electrode. Thus, we immobilized glucose oxidase (GOD) as a model enzyme on the nanocomposite-based electrode with a thin layer of Nafion to fabricate a glucose biosensor, which showed sensitive and fast response to glucose. The influence of the GOD loading was investigated and the biosensor with an enzyme loading concentration of 10 mg/mL shows optimal performance for glucose detection, that is, a detection limit of 3 μM and a response time of 3 s, respectively.     

Preparation of Multiwall Carbon Nanotubes-supported High Loading Platinum for Vehicular PEMFC Application

Multiwall carbon nanotube-supported Pt （Pt/MWNTs） catalysts with high dispersion and high loading of Pt were prepared by chemical reduction method and the loading of Pt got to 40 wt%. The average diameter of Pt nanoparticles on MWNTs was about 3.5 nm. When the hydrogen and air were used as reactant gases for PEMFC, Pt/MWNTs catalysts showed significantly higher performance than the Pt/XC-72 （carbon black） catalysts.     

Nanostructure PtRu/MWNTs as anode catalysts prepared in a vacuum for direct methanol oxidation

Platinum and ruthenium nanoparticles that are uniformly dispersed on multiwalled carbon nanotubes (MWNTs) were synthesized by vacuum pyrolysis using Pt(acac)2 and Ru(acac)3 as the metal precursors. The resulting nanocomposites were characterized by transmission electron microscopy and X-ray diffraction. The Pt, Pt45Ru55, and Ru nanoparticles had mean diameters of 3.0 +/- 0.6, 2.7 +/- 0.6, and 2.5 +/- 0.4 nm and the same mole number as their metal precursors at 500 degrees C. The electrocatalytic activity of the Pt/MWNTs and PtRu/MWNTs was investigated at room temperature by cyclic voltammetry and chronoamperometry. All of the electrochemical results showed that the PtRu/MWNTs exhibited a high level of catalytic activity for methanol oxidation as a result of the large surface area of the supporting carbon nanotubes and the wide dispersion of the Pt and Ru nanoparticles. Compared with the Pt/MWNTs, the onset potential for methanol oxidation of the PtRu/MWNTs was significantly lower, and the ratio of the forward anodic peak current to the reverse anodic peak current during methanol oxidation was somewhat higher. The Pt45Ru55/MWNTs displayed the best electrocatalytic activity of all of the carbon-nanotube-supported Pt and PtRu catalysts.     

研究表面扩散的双电解池方法及其在铂钌二元金属电催化研究中的应用

本文介绍一种由各自质子交换膜(作为电解质),参比电极和对电极在同一个工作电极上建立两个空间分离的、可独立控制的双电解池系统.它能够由第1个恒电位仪控制的第1电解池的工作电极产生某种吸附中间物,该中间物通过表面扩散到达第2个电解池的工作电极后,在第2个恒电位仪的控制下得到电化学检验.应用这一装置测量了铂电极上欠电势沉积的含氧吸附物种的表面扩散系数,并研究模拟铂钌电极电氧化有机小分子产生的毒性中间物与表面含氧吸附物种的相互作用.在质子交换膜燃料电池的燃料极的工作电势下,没有发现钌表面产生的含氧吸附物种扩散到铂的表面.作者据此假设Pt Ru协同催化作用的实现可能是由于铂上毒性中间物的表面扩散速率非常慢,限制了向钌表面的溢流速率.只有当Pt Ru边界足够大,中间物在铂表面扩散途径非常短时才能形成足够的流速,并在钌表面被表面含氧物种氧化成CO2,使铂表面被重新活化.     

Nanostructured Pt functionlized multiwalled carbon nanotube based hydrogen sensor

Nanostructured Pt functionalized multiwalled carbon nanotubes (MWNTs) produced by catalytic chemical vapor deposition are good room-temperature hydrogen sensors. MWNTs have been synthesized by catalytic chemical vapor deposition of acetylene using a fixed-bed catalytic reactor over hydrides of Mm(0.2)Tb(0.8)CO2 obtained through hydrogen decrepitation technique. Purified and chemically treated MWNTs have been functionalized by Pt resulting in nanostructured dispersion of Pt on CNTs. Structural, morphological, and vibrational characterizations have been carried out using XRD, SEM, TEM, HRTEM, Raman spectroscopy, and FTIR spectroscopy, respectively. Dispersion of Pt on MWNTs was confirmed by elemental analysis using EDX. Systematic investigations of hydrogen sensing properties of Pt-MWNT ensembles have been carried out. The Pt-MWNTs thin films are stable after several cycles of adsorption and desorption. The change in electrical resistance due to hydrogen adsorption is reversible, with increases to saturation on exposure to hydrogen gas. The result demonstrates that the Pt-MWNTs are p-type semiconductor materials, and chemically treated MWNTs functionalized with Pt show the better hydrogen sensing response at room temperature.     

Some Properties of Sodium Dodecyl Sulfate Functionalized Multiwalled Carbon Nanotubes Electrode and Its Application on Detection of Dopamine in the Presence of Ascorbic Acid

A sodium dodecyl sulfate (SDS) functionalized multiwalled carbon nanotubes (MWNTs) electrode (SDS/MWNTs) was successfully constructed in this study. The electrochemical property of the SDS/MWNTs electrode has been characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Nyquist plots suggest that the immersion time of SDS affects the resistances of the MWNTs electrodes. The thickness of adsorbed SDS on MWNTs surface is estimated to be 1.23 nm, which is close to the value of SDS monolayer. CV results demonstrate a 5‐fold enhanced response for dopamine (DA) at the SDS/MWNTs electrode compared to the bare MWNTs one. DPV results illustrate that DA can be selectively determined in the presence of high concentration ascorbic acid (AA) with a linear range from 20 μM to 0.20 mM and a sensitivity of 0.024 μA μM^?1 at the SDS/MWNTs electrode.     

Spontaneous formation of platinum particles on electrodeposited palladium

Pt particles have been spontaneously formed on the electrochemically deposited Pd layer on ITO substrate. SEM reveals that the Pt particles spontaneously formed on the Pd surface are uniformly distributed. The as-prepared material (denotes as Pt–Pd/ITO) as electrode shows a higher activity for ethanol oxidation than that of Pd/ITO. The mechanism is tentatively explained as that the H dehydrogenated from ethanol on Pt can efficiently spillover to the underneath Pd, resulting in an enhanced kinetics. The rapid removal of H on the Pt active sites accelerates the further adsorption of ethanol and dehydrogenation (oxidation). This work demonstrates a strategic method to spontaneous prepare small particles on the reductive species-containing substrates. The metal ion with a higher standard potential than that of hydrogen is theoretically possible to be spontaneously reduced to metal on hydrogenated Pd.     

Hydrophobic adsorption of surfactants on water-soluble carbon nanotubes: A simple approach to improve sensitivity and antifouling capacity of carbon nanotubes-based electrochemical sensors

Water-soluble multi-walled carbon nanotubes (MWNTs) were prepared by the strong adsorption of Congo red (CR) on MWNTs. The CR-functionalized MWNTs (MWNTs–CR) had a high solubility, a high purity and a special property of strong rebundling when dried, capable of forming uniform and compact MWNTs films with a 3D network structure of nanosizes on a glassy carbon electrode (GCE). Compared with GCE, the electrochemical response of estradiol at a MWNTs–CR modified glassy carbon electrode (MWNTs–CR/GCE) was greatly enhanced, which was further amplified by the addition of trace cetyltrimethylammonium bromide (CTAB) in solution, along with the accomplishment of antifouling capacity of the modified electrode. The weak hydrophobic adsorption of surfactants on the hydrophobic and smooth surface of MWNTs was found to be the key for simultaneously improving the sensitivity and antifouling capacity of carbon nanotube-based electrochemical sensors by surfactants.     

An EC-FTIR study on the catalytic role of Pt in carbon corrosion

In this study, we investigate the role of Pt in the corrosion of carbon by Fourier-transformed infrared spectroscopy coupled in situ with electrochemical measurements. We confirm that the carbon corrosion rate is strongly enhanced in the presence of Pt and shed light on the reaction mechanisms at both anode and cathode potentials. It is shown that carbon surface oxide species (phenol, ether, carboxylic and carbonyl groups), formed at low electrode potential E < 0.60 V vs. RHE, spillover back from the carbon support to the Pt nanoparticles, where they are converted into CO and then slowly oxidized into CO₂. At higher electrode potential E > 0.60 V vs. RHE, oxygenated species resulting from water splitting on Pt facilitate the removal of these carbon surface oxides species yielding increased kinetics for carbon corrosion.     

Preparation and electrocatalytic activities of platinum nanoclusters deposited on modified multi-walled carbon nanotubes supports

Multi-walled carbon nanotubes (MWNTs) were modified by oxyfluorination treatment at several different temperatures of 20, 100, 200, and 300 °C. The changes of surface properties of oxyfluorinated MWNTs were investigated using X-ray photoelectron spectroscopy (XPS) method. As a result, it was found that surface fluorine contents were varied with changing an oxyfluorination temperature and showed a maximum value at 100 °C. By changing the treatment temperature in the process of oxyfluorination for carbon supports, the surface characteristics of MWNTs had been modified, resulting that the size and loading content of deposited Pt on the modified carbon supports could be changed. Consequently, Pt deposited MWNTs that were treated at 100 °C (Pt/100-MWNTs) showed the best electroactivity among samples. The enhanced electroactivity was dependent on the higher surface area of electrochemical reaction for metal catalyst, which was related to the particle size and the morphology of the deposited particle catalysts.     

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.     

Electrochemical Reduction of Oxygen on Multi-walled Carbon Nanotubes Electrode in Alkaline Solution

The multi-walled carbon nanotubes (MWNTs) electrode was constructed using polytetrafluoroethylene as binder, and the electrochemical reductive behavior of oxygen in alkaline solution was first examined on this electrode. Compared with other carbon materials, MWNTs show higher electrocatalytic activity, and the reversibility of O2 reduction reaction is greatly improved. The experiments reveal that the electrochemical reduction of O2 to HO2 is controlled by adsorption. The preliminary results illustrate the potential application of MWNTs in fuel cells.     

Amperometric Biosensors for Glucose Based on Layer‐by‐Layer Assembled Functionalized Carbon Nanotube and Poly (Neutral Red) Multilayer Film

Abstract

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer‐by‐layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron‐transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long‐term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR‐modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite‐modified GC electrode is more than three‐fold greater than that of the MWNTs modified GC electrode, and nine‐fold greater than that of the PNR‐modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference‐free determination of glucose has been realized at ?0.2 V vs. SCE with a linear range from 50 µM to 10 mM and response time <10s. The detection limit was 10 µM glucose (S/N=3).     

Self-assembly of bilayer lipid membrane at multiwalled carbon nanotubes towards the development of photo-switched functional device

Bilayer lipid membrane (BLM) was self-assembled on a uniquely fabricated hydrophilic surface, containing N atoms from the carbon source of ethylene amine, of the multi-walled carbon nanotubes (MWNTs) to form the BLM/MWNTs nanocomposites. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and photoelectric experiments were taken to study the properties of the BLM/MWNTs nanocomposites. The thickness of the BLM, which was calculated from the CV data obtained at BLM/MWNTs electrode, turned out to be 4.38 nm, suggesting that the lipid self-assembled at the nanotubes surface was consistent with a bilayer structure. C₆₀-incorporated BLM could also be self-assembled at the nanotubes surface (C₆₀-BLM/MWNTs). The formation of BLM on the MWNTs surface blocked the diffusion of [Fe(CN)₆]^3/4− redox ions across BLM to the MWNTs electrode as no redox current was observed by CV measurement, whereas the incorporation of the electron mediator, C_60, resumed a pair of redox peaks at C₆₀-BLMs/MWNTs electrode. Moreover, the incorporation of C₆₀ led to a four order of magnitude reduction of the resistance of C₆₀-BLM/MWNTs (369.3 Ω) than that of BLM/MWNTs (3.238 × 10⁶ Ω). MWNTs electrode exhibited an intrinsic cathodic photocurrent (166 μA cm⁻²) while BLM/MWNTs electrode blocked photocurrent response of the MWNTs. Interestingly, C₆₀-BLM/MWNTs electrode resumed partial photoelectric properties (photo current: 65 μA cm⁻²) due to the electron mediation effect of C₆₀ incorporated into the lipid membrane. As a result, the novel self-assembled BLM/MWNTs nanocomposites provided a simple yet useful model to study the C₆₀-mediated photoelectric properties of the BLM/MWNTs which may be applicable to develop new biosensors and molecular devices.     

The fabrication of a colloidal gold-carbon nanotubes composite film on a gold electrode and its application for the determination of cytochrome c

Colloid Au (Au_nano) with a diameter of about 20 nm was prepared and used in combination with the multi-wall carbon nanotubes (MWNTs) to modify a gold electrode. Dihexadecylphosphate (DHP) dispersed in Au_nano aqueous solution was used to solubilize MWNTs. Deposition of Au_nano on MWNTs was realized as illustrated by TEM micrographs. The DHP formed a network that connected Au_nano and MWNTs to the gold electrode surface. The Au_nano–MWNTs–DHP composite film on the gold electrode surface was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammmetry (CV). The composite film modified gold electrode was used to detect cytochrome c and a pair of well-defined redox waves was obtained. It was found that the composite film promoted the redox of horse heart cytochrome c and its effect was developed for the determination of cytochrome c.