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.     

Nanoscale azo pigment immobilized on carbon nanotubes via liquid phase reprecipitation approach

Nanoscale azo pigment immobilized on the outer shell of multiwalled carbon nanotubes (MWCNT–AZO) were prepared by modified liquid phase reprecipitation method, and the MWCNT–AZO hybrid was characterized by means of TEM, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV–VIS absorption. The photoconductivity of single-layered photoreceptors, where MWCNT–AZO served as the charge generation material (CGM), was studied by the xerographic photoinduced discharge method. The results indicated that the MWCNT–AZO nano hybrid showed broader and enhanced photosensitivity than MWCNT/bulk azo pigments (AZO) blend or the bulk AZO did, which was interpreted in terms of nanometer size effect of MWCNT–AZO hybrid and charge transfer from AZO nanoparticles to MWCNT.     

Fabrication of an electrochemical platform based on the self-assembly of graphene oxide-multiwall carbon nanotube nanocomposite and horseradish peroxidase: direct electrochemistry and electrocatalysis

A novel hybrid nanomaterial (GO-MWNTs) was explored based on the self-assembly of multiwall carbon nanotubes (MWNTs) and graphene oxide (GO). Compared with pristine MWNTs, such a nanocomposite could be well dispersed in aqueous solution and exhibit a negative charge. Driven by the electrostatic interaction, positively charged horseradish peroxidase (HRP) could then be immobilized onto GO-MWNTs at the surface of a glassy carbon (GC) electrode to form a HRP/GO-MWNT/GC electrode under mild conditions. TEM was used to characterize the morphology of the GO-MWNT nanocomposite. UV-vis and FTIR spectra suggested that HRP was immobilized onto the hybrid matrix without denaturation. Furthermore, the immobilized HRP showed enhanced direct electron transfer for the HRP-Fe(III)/Fe(II) redox center. Based on the direct electron transfer of the immobilized HRP, the HRP/GO-MWNT/GC electrode exhibited excellent electrocatalytic behavior to the reduction of H(2)O(2) and NaNO(2), respectively. Therefore, GO-MWNTs could provide a novel and efficient platform for the immobilization and biosensing of redox enzymes, and thus may find wide potential applications in the fabrication of biosensors, biomedical devices, and bioelectronics.     

Electrocatalytic reduction of chloramphenicol at multiwall carbon nanotube-modified electrodes

A multiwall carbon nanotube-modified glassy carbon (GC) electrode was employed for the investigation of chloramphenicol (CAP) reduction. Carbon nanotube coating can greatly lower the overpotential of the electrochemical reduction of CAP and promote the electrode reaction. CAP undergoes an irreversible reduction process in phosphate buffer by the modified electrode. The reduction peak current (Ip) was significantly increased. Effects of some important factors, including pH, scan rate, and amount of modifier, on the determination of CAP were investigated. In the range of 3 x 10(-7) to 1.2 x 10(-5) M, the reduction peak current (Ip) has a good linear relationship with the concentration of CAP. When the signal-to-noise ratio is 3, the detection limit is 4.5 x 10(-8) M. The relative standard deviation of 10 measurements for 3 x 10(-6) M CAP is 5.3%, suggesting an excellent reproducibility of the modified electrode. Interfering experiments show that the modified electrode has excellent selectivity for the detection of CAP. The modified electrode was used to determine CAP in eyedrops, and the recoveries were approximately 100%.     

Preparation,electrochemical behavior and electrocatalytic activity of chlorogenic acid multi-wall carbon nanotubes as a hydroxylamine sensor

Electrochemical characteristics of an electrodeposited chlorogenic acid film on multi-wall carbon nanotubes glassy carbon electrode (CGA–MWCNT–GCE) and its role as a sensor for electrocatalytic oxidation of hydroxylamine are described. Cyclic voltammograms of the CGA–MWCNT–GCE indicate a pair of well-defined and nearly reversible redox couple with the surface confined characteristics at a wide pH range of 2.0–12.0. The charge transfer coefficient, α, and the charge transfer rate constant, k_s, of CGA adsorbed on MWCNT were calculated 0.48 and 44 ± 2 s^?1 respectively. The CGA–MWCNT–GCE shows a dramatic increase in the peak current and/or a decrease in the overvoltage of hydroxylamine electrooxidation in comparison with that seen at a CGA modified GCE, MWCNT modified GCE and activated GCE. The kinetic parameters of electron transfer coefficient, α, the heterogeneous electron transfer rate constant, k′, and exchange current, i₀, for oxidation of hydroxylamine at the modified electrode surface were determined using cyclic voltammetry. Four linear calibration ranges and high repeatability with relative standard deviation of 4.6%, for a series of four successive measurements in 17.7 μM hydroxylamine, are obtained at the CGA–MWCNT–GCE using an amperometric method. Finally, the modified electrode was successfully used for determination of spiked hydroxylamine in two water samples.     

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.     

Study of different carbon materials for amperometric enzyme biosensor development

Diamond-like carbon (DLC) electrodes which constitute a new research area in electrochemistry and glassy carbon (GC) electrodes were used as transducers for fabrication of glucose oxidase (GOD) biosensors. The amperometric signal of the enzyme electrode was due to the electro-oxidation of H₂O₂ generated in the enzyme layer. This work has shown that the detection limit of glucose on GOD/GC electrode is 20 μM while it is 50 μM on GOD/DLC electrode. The sensitivity of GOD/GC electrode decreases 4% after 8 days and we have good repeatability of measurements for GOD/DLC electrode in the same day.     

Synthesis and relevant electrochemical properties of 2-hydroxypropyltrimethyl ammonium chloride chitosan-grafted multiwalled carbon nanotubes

The 2-hydroxypropyltrimethyl ammonium chloride chitosan (HACC)-grafted multiwalled carbon nanotubes (MWCNTs) composite (HACC–MWCNTs) was prepared via covalently grafting HACC onto the surfaces of MWCNT. The properties and morphology of the resulting materials were monitored by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The results of FTIR and TGA indicated that the interaction between MWCNT and HACC was grafting through covalent links. TEM and SEM images confirmed MWCNT stained with an extra phase after the grafting process that was presumed to come from HACC. The dispersion of MWCNT in H₂O was improved after the grafting of HACC,which was in agreement with the positive charge of HACC–MWCNT at any pH value. The electrochemical properties of HACC–MWCNT were investigated by cyclic voltammetry (CV). The dramatic improvement in the electrostatic interactions between HACC–MWCNT/electrode and anionic complexes was distinguished from the response of chitosan-MWCNT/electrode and non-modified electrode. According to the experimental results, the HACC–MWCNT had a possibility to serve as a novel material for innovative anionic sensor.     

Amperometric determination of hydrogen peroxide by functionalized carbon nanotubes through EDC/NHS coupling chemistry

The electrochemistry of the redox mediator Toluidine blue (TB) which was covalently linked to the carboxyl group of the multiwalled carbon nanotubes (MWNTs) by coupling reactions, in which N-hydroxysuccinimide was used to assist 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride catalyzed amidation reaction is described. The results from cyclic voltammetry (CV) and amperometry suggested that the redox mediator is linked to the surface of the MWNTs and the nanotubes showed an obvious promotion for the direct electron-transfer between the redox mediator and the electrode. A couple of well-defined redox peak of TB was observed in a phosphate buffer solution (pH 7.0). The redox mediator immobilized to MWNTs exhibits remarkable electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). The analytical applicability of the modified electrode for the determination of hydrogen peroxide was examined. A linear response in the concentration range of 6.8 x 10(-7)-3.4 x 10(-2) M (r = 0.9958) was obtained with detection limit of 3.4 x 10(-7) M for the determination of hydrogen peroxide. The modified electrode has advantages of being highly stable, sensitive, ease of construction and use.     

纳米Fe3O4-还原氧化石墨烯复合修饰玻碳电极的制备及电化学检测多巴胺

通过电化学还原法制备纳米Fe₃O₄-还原氧化石墨烯复合修饰玻碳（Fe₃O₄-rGO/GCE）电极,用于多巴胺（DA）的检测。采用SEM、TEM和循环伏安对纳米Fe₃O₄-rGO复合材料进行表征。在pH为7.0的磷酸盐缓冲液（PBS）中,采用循环伏安法研究了DA在纳米Fe₃O₄-rGO/GC上的电化学行为。实验结果表明,较裸GC电极和rGO修饰（rGO/GC）电极,由于纳米Fe₃O₄与rGO的协同作用,纳米Fe₃O₄-rGO/GC显著增大了Fe₃O₄-rGO/GC复合材料电极电化学活性面积和氧化峰电流强度i_pa。DA的浓度在6.0×10^-8~2.0×10^-6 mol/L和2.0×10^-6~8.0×10^-5 mol/L范围内,与氧化峰电流强度i_pa呈良好的线性关系,检出限达4.0×10^-9 mol/L（信噪比S/N=3）。抗坏血酸和尿酸共存物几乎不干扰DA的测定,选择性高。Fe₃O₄-rGO/GC修饰电极用于盐酸DA注射液中的DA含量测定,获得结果较好,回收率为97.1%~103.9%。     

Fabrication and electrocatalysis of self-assembly directed gold nanoparticles anchored carbon nanotubes modified electrode

A self-assembly directed approach was adopted to modify glassy carbon electrode (GC) with gold nanoparticles incorporation and the electrocatalytic performance of self-assembly modified electrode, GC/SA-Au-ME was critically evaluated for the oxidation of ascorbic acid (AA). The modification involves the dispersion of multi-wall carbon nanotube (MWNT) and an inclusion complex, beta-cyclodextrin-4-aminothiophenol on the surface of GC electrode in the presence of cetyltrimethylammonium bromide (CTAB). Gold nanoparticles were deposited into the self-assembled sites to fabricate the modified electrode, GC/SA-Au-ME. Another electrode (GC-Au-ME) was fabricated under similar conditions in the absence of CTAB. The electrocatalytic activity of the modified electrodes (GC/SA-Au-ME and GC-Au-ME) towards the oxidation of AA was critically compared. Cyclic voltammetry, chronoamperometry, and double potential chronoamperometry were used to evaluate the characteristics of the modified electrodes. The self-assembled electrode (GC/SA-Au-ME) shows excellent electrocatalytic activity over the other electrode, GC-Au-ME. Augmented current response, faster electron transfer kinetics (with a rate constant for electron transfer process as 3.25 x 10(4) cm3 mol(-1) s(-1)), linear range of response for the analyte (1-50 mM with an extended detection limit to 1 microM), better sensitivity, and selectivity were witnessed for the self-assembly directed modified electrode.     

Electrocatalytic detection of NADH and glycerol by NAD(+)-modified carbon electrodes

The electrochemical oxidation of the adenine moiety in NAD+ and other adenine nucleotides at carbon paste electrodes gives rise to redox-active products which strongly adsorb on the electrode surface. Carbon paste electrodes modified with the oxidation products of NAD+ show excellent electrocatalytic activity toward NADH oxidation, reducing its overpotential by about 400 mV. The rate constant for the catalytic oxidation of NADH, determined by rotating disk electrode measurements and extrapolation to zero concentration of NADH, was found to be 2.5 x 10(5) M-1 s-1. The catalytic oxidation current allows the amperometric detection of NADH at an applied potential of +50 mV (Ag/AgCl) with a detection limit of 4.0 x 10(-7) M and linear response up to 1.0 x 10(-5) M NADH. These modified electrodes can be used as amperometric transducers in the design of biosensors based on coupled dehydrogenase enzymes and, in fact, we have designed an amperometric biosensor for glycerol based on the glycerol dehydrogenase (GlDH) system. The enzyme GlDH and its cofactor NAD+ were co-immobilized in a carbon paste electrode using an electropolymerized layer of nonconducting poly(o-phenylenediamine) (PPD). After partial oxidation of the immobilized NAD+, the modified electrode allows the amperometric detection of the NADH enzymatically obtained at applied potential above 0 V (Ag/AgCl). The resulting biosensor shows a fast and linear response to glycerol within the concentration range of 1.0 x 10(-6)-1.0 x 10(-4) M with a detection limit of 4.3 x 10(-7) M. The amperometric response remains stable for at least 3 days. The biosensor was applied to the determination of glycerol in a plant-extract syrup, with results in good agreement with those for the standard spectrophotometric method.     

多壁纳米碳管电极电吸附脱盐性能的研究

利用透射电镜(TEM)和X射线衍射(XRD)对多壁纳米碳管形貌和晶型结构进行分析,发现多壁纳米碳管管径分布范围窄,其层间距大于高定向石墨,且随着管径的增大逐渐减小;利用多壁纳米碳管对氮气吸附实验分析其表面结构,发现其比表面积和孔容随管径的增大而减小,所形成的空隙绝大部分为中孔;将多壁纳米碳管处理后,压制成电极,组装成电吸附脱盐器,研究纳米碳管管径对电极电容和脱盐性能的影响,结果表明多壁纳米碳管管径越小,电极比电容越高,脱盐能力越强,随着中孔比表面积增大电极比电容和电极单位脱盐量均呈线性增加。     

Facile deposition of polyvinylpyrrolidone-grafted multi-walled carbon nanotube on glassy carbon electrode and its application in the sensing of biomolecules

Polyvinylpyrrolidone-grafted multi-walled carbon nanotube (PVP/MWCNT) was deposited on carboxylated glassy carbon electrode (GCE) from acidic water via the electrostatic force between the positively charged PVP/MWCNTs and negatively charged GCE. It was found out that PVP/MWCNT-modified GCE (PVP/MWCNT/GCE) exhibited great catalytic capability for the oxidation of dopamine (DA), uric acid (UA), tyrosine (Tyr) and nitrite) by enhancing their oxidation currents and lowering their overpotentials. For PVP/MWCNT/GCE, the linear calibration plots for DA, UA, Tyr and nitrite were obtained over the range of 0.1–50 μM, 1–500 μM, 1–200 μM and 1–500 μM with detection limits of 0.04 μM, 0.17 μM, 0.26 μM and 0.30 μM, respectively. In addition, satisfactory results were obtained by applying PVP/MWCNT/GCE in the determination of DA, UA, Tyr and nitrite in human serum samples with standard addition method.     

Direct determination of oxalic acid by a bare platinum electrode contrasting a platinum nanoparticles-modified glassy carbon electrode

A bare platinum disk electrode without further decoration was directly used to determine oxalic acid (OA), showing good linear ranges of 0.57–104.01 μM and 104.01–228.75 μM with a low detection limit of 0.38 μM (S/N = 3). In contrast, platinum nanoparticles (PtNPs) dispersed on a glassy carbon electrode were successfully achieved by an one-step electrochemical deposition method, possessing relatively wider linear detection ranges of 1.14–342.80 μM and 342.80–548.92 μM for OA with a lower detection limit of 0.28 μM (S/N = 3). Both the proposed electrochemical sensors exhibit great reproducibility, stability and selectivity. In particular, they have been applied to the determination of OA in real spinach samples, showing excellent analytical performance.     

Electrochemical biosensing platforms using platinum nanoparticles and carbon nanotubes

Platinum nanoparticles with a diameter of 2-3 nm were prepared and used in combination with single-wall carbon nanotubes (SWCNTs) for fabricating electrochemical sensors with remarkably improved sensitivity toward hydrogen peroxide. Nafion, a perfluorosulfonated polymer, was used to solubilize SWCNTs and also displayed strong interactions with Pt nanoparticles to form a network that connected Pt nanoparticles to the electrode surface. TEM and AFM micrographs illustrated the deposition of Pt nanoparticles on carbon nanotubes whereas cyclic voltammetry confirmed an electrical contact through SWCNTs between Pt nanoparticles and the glassy carbon (GC) or carbon fiber backing. With glucose oxidase (GOx) as an enzyme model, we constructed a GC or carbon fiber microelectrode-based biosensor that responds even more sensitively to glucose than the GC/GOx electrode modified by Pt nanoparticles or CNTs alone. The response time and detection limit (S/N = 3) of this biosensor was determined to be 3 s and 0.5 microM, respectively.     

Metallic nanoparticle-carbon nanotube composites for electrochemical determination of explosive nitroaromatic compounds

Metal nanoparticles (Pt, Au, or Cu) together with multiwalled and single-walled carbon nanotubes (MWCNT and SWCNT) solubilized in Nafion have been used to form nanocomposites for electrochemical detection of trinitrotoluene (TNT) and several other nitroaromatics. Electrochemical and surface characterization by cyclic voltammetry, AFM, TEM, SEM, and Raman spectroscopy confirmed the presence of metal nanoparticles on CNTs. Among various combinations tested, the most synergistic signal effect was observed for the nanocomposite modified glassy carbon electrode (GC) containing Cu nanoparticles and SWCNT solubilized in Nafion. This combination provided the best sensitivity for detecting TNT and other nitroaromatic compounds. Adsorptive stripping voltammetry for TNT resulted in a detection limit of 1 ppb, with linearity up to 3 orders of magnitude. Selectivity toward the number and position of the nitro groups in different nitroaromatics was very reproducible and distinct. Reproducibility of the TNT signal was within 7% (n = 8) from one electrode preparation to another, and the response signal was stable (+/-3.8% at 95% confidence interval) for 40 repeated analyses with 10 min of preconditioning. The Cu-SWCNT-modified GC electrode was demonstrated for analysis of TNT in tap water, river water, and contaminated soil.     

氮掺杂多孔碳负载铜钴纳米复合材料的制备及其电催化性能EI北大核心CSCD

先以ZIF-8作为前驱体采用简单的高温炭化法制备出氮掺杂多孔碳纳米多面体(NPC),再通过一步化学还原法将铜和钴颗粒负载到多孔碳上,成功制备出Cu@Co/NPC纳米复合材料。运用X射线粉末衍射仪、透射电子显微镜和X射线光电子能谱等手段对复合材料进行表征,将该复合材料修饰到玻碳电极表面上,研究其对肼的电化学响应。结果表明,Cu@Co/NPC纳米复合材料发挥出协同作用,从而对肼展现出比单一组分修饰电极更优异的电催化作用。在优化的实验条件下,复合材料修饰电极与肼的浓度在5~1850μmol/L范围内呈良好的线性关系,检测限达0.08μmol/L。此外,该复合材料修饰电极测定肼的稳定性、重现性以及选择性均较好,已被成功用于环境水样中肼的检测,结果令人满意。     

MWCNTs/Cu(OH)2 nanoparticles/IL nanocomposite modified glassy carbon electrode as a voltammetric sensor for determination of the non-steroidal anti-inflammatory drug diclofenac

This paper describes the development and utilization of a new nanocomposite consisting of Cu(OH)₂ nanoparticles, hydrophobic ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆) and multiwalled carbon nanotubes for glassy carbon electrode modification. The nanocomposite was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM) along with energy-dispersive X-ray spectroscopy (EDX). The modified electrode was used for electrochemical characterization of diclofenac. Using differential pulse voltammetry, the prepared sensor showed good sensitivity and selectivity with low overpotential for the determination of diclofenac in the range from 0.18 to 119 μM, with a detection limit of 0.04 μM. Electrochemical studies suggested that the MWCNTs/Cu(OH)₂ nanoparticles/IL nanocomposite modified electrode provided a synergistic augmentation on the voltammetric behavior of electrochemical oxidation of diclofenac, which was indicated by the improvement of anodic peak current.     

Optimization and characterization of a flow injection electrochemical system for pentachlorophenol assay

A flow injection (FI) electrochemical detection system has been developed and optimized for the determination of pentachlorophenol (PCP) in contaminated soil. PCP was oxidized to tetrachloro-1,4-benzoquinone (1,4-TCBQ) with a high yield using bis(trifluoroacetoxy)iodobenzene in 0.1 M tartaric acid, pH 2.0, at ambient temperature. Upon rapid reaction with immobilized glucose oxidase, the detection and amplification scheme was completed as the reduced form of 1,4-TCBQ or tetrachloro-1,4-hydroquinone was reoxidized to 1,4-TCBQ at the surface of the glassy carbon electrode (+ 0.40 V vs Ag/AgCl). Rapid electron exchange between the enzyme and its glucose substrate provided a non-rate-limiting current toward the electrode. The FI electrochemical system was linear up to 1 μM oxidized PCP with a detection limit of 10 nM and exhibited a reproducibility of ±0.6% over 165 repeated analyses during 14 h of continuous operation. When applied to PCP-contaminated soil samples, the results obtained from the FI electrochemical system compared well with those of the HPLC standard method.