电化学石英晶体微天平研究重氮盐的电还原过程

采用压电电化学石英晶体微天平(EQCM)技术研究了硫酸重氮盐在裸金电极(Au)和多壁碳纳米管(MWCNTs)修饰金电极上的电还原行为,比较了2种电极上电沉积质量和稳定性。结果表明,相同循环伏安扫描条件下,重氮盐在金电极和MWCNTs/Au电极上的工作曲线还原峰电位相同,后者的初始峰电流低于前者,QCM数据显示重氮盐在MWCNTs/Au电极上沉积速度优于金电极,饱和沉积量是金电极上的3倍,表明碳纳米管催化了还原过程并增大了电极的表面积;在磷酸中性缓冲溶液中浸泡7 d后,重氮盐修饰后的MWCNTs/Au电极表面质量变化比金电极小0.28ng,表明修饰后的MWCNTs/Au电极略稳定。     

单宁酸在碳掺杂蒙脱土修饰电极上的电化学行为及测定

制备了碳掺杂蒙脱土修饰电极(C-MMT/GCE),采用循环伏安法研究了单宁酸在该修饰电极上的电化学行为。结果表明,该电极过程受吸附-扩散混合控制,转移电子数等于质子数n=m=1,电极有效面积A eff=0.092 cm2,扩散系数D=1.66×10-5cm2/s。单宁酸的氧化峰电流与其浓度在8.0×10-6~4.0×10-4mol/L呈线性关系,检出限为1.0×10-6mol/L,并测得单宁酸试样的回收率为97.6%~102.8%。该修饰电极具有良好的重现性。     

鞣酸在玻碳电极上的电化学行为与检测

本文采用循环伏安法研究了鞣酸在玻碳电极上的电化学行为,并讨论了电解质溶液、溶液pH、扫描速率等因素的影响。测定了电极反应的部分动力学参数。结果表明,该电极过程受吸附-扩散混合控制,反应转移的电子数与质子数相等即m=n=1,电极有效面积A=10.60mm~2,扩散系数D=4.315×10~(-5)cm~2·s~(-1)。其氧化峰电流在1.0×10~(-4)~2.0×10~(-6)mol·L~(-1)范围内呈线性关系,检测限为1.0×10~(-6)mol·L~(-1),加标回收率为98.92%~103.0%。     

多巴胺在石墨烯/多壁碳纳米管电极上的电化学行为

采用滴涂法在玻碳电极上修饰氧化石墨烯及多壁碳纳米管,通过电化学还原方法制备石墨烯/多壁碳纳米管复合材料及相应修饰电极(ERGO/MWCNTs/GCE)。运用循环伏安法研究多巴胺(DA)在修饰电极上的电化学行为。研究表明:与裸玻碳电极相比,多巴胺在修饰电极上氧化峰与还原峰电位差为70 m V,峰电流显著提高,表明该电极对多巴胺具有较好的催化氧化作用。高浓度抗坏血酸的存在不影响多巴胺的测定。在优化实验条件下,多巴胺在4.8×10~(-7)~1.1×10~(-5)mol/L和1.1×10~(-5)~2.93×10~(-4)mol/L范围内呈良好的线性关系,检出限为8.7×10~(-8)mol/L,RSD为4.3%。     

四环素在MWCNTs/GCE和Graphene/GCE上的电化学行为研究北大核心

电化学氧化技术在四环素类抗生素废水处理过程中存在氧化电位高,且电极发生严重腐蚀等现象,通过对电极进行修饰,以降低电极的过电势,增加电流响应,提高电极的选择性和灵敏度。本文采用滴涂法分别制备了多壁碳纳米管修饰电极(MWCNTs/GCE)和石墨烯修饰电极(Graphene/GCE),采用循环伏安法和交流阻抗法对修饰电极电化学性能进行了表征。结果表明修饰材料已经成功修饰在电极表面;通过对比四环素在两种修饰电极上的电化学行为,发现四环素在MWCNTs/GCE电极上的电化学响应信号明显,且氧化峰电位明显降低。     

脉冲电沉积氧化石墨烯纳米带修饰电极测定盐酸四环素

以多壁碳纳米管为原料制备氧化石墨烯纳米带(GONRs),通过红外光谱、紫外-可见吸收光谱和拉曼光谱对其进行表征。将制备好的GONRs脉冲电沉积到玻碳电极(GCE)表面制备修饰电极(GONRs/GCE),研究了盐酸四环素(TC)在GONRs/GCE上的电化学行为。结果表明,与裸玻碳电极相比,GONRs/GCE对TC有更高的电催化活性。TC在GONRs/GCE上发生受吸附控制的不可逆氧化反应,且在pH 3.0的柠檬酸-柠檬酸钠缓冲溶液中氧化峰电流最高。优化条件下,TC的氧化峰电流与浓度线性相关,线性范围为4.0×10~(-7)～1.0×10~(-4) mol/L,最低检测限为2.0×10~(-7) mol/L(S/N=3)。将该电极用于河水样品中TC的检测,加标回收率为97.2%～104.1%。     

氧化苦参碱在纳米金与硫化铜石墨烯复合修饰碳糊电极上的电化学行为及电分析方法研究

本文研究了氧化苦参碱(MOT)在纳米金(AuNPs)和硫化铜石墨烯(CuS-Gr)复合修饰碳糊电极(AuNPs-CuS-Gr/CPE)上的电化学行为。实验结果表明,与CPE相比,AuNPs-CuS-Gr/CPE对氧化苦参碱具有明显的电催化效果,其氧化峰电流显著增加。同时用循环伏安法(CV)、计时电流法(CA)测定了MOT在AuNPs-CuS-Gr/CPE上的电极反应动力学参数,用微分脉冲伏安法(DPV)法测得MOT氧化峰电流与浓度的线性范围为8.0×10~(-4)~1.0×10~(-1) mol/L,检出限(LOD,S/N=3)为3.3×10~(-7) mol/L,同时应用于市售氧化苦参碱针剂的检测,RSD在0.40%~3.4%之间,回收率达98.4%~100.8%,检测结果符合电化学定量测定要求。     

机械球磨对碳纳米管电化学性能的影响

通过改变机械球磨时间制备了不同长度的多壁碳纳米管(MWNTs).透射电子显微镜(TEM)显示随着球磨时间的增加,碳纳米管的长度变短,管壁缺陷增多.利用循环伏安(CV)和交流阻抗(EIS)考察了球磨0、0.5、2、5 h MWNTs修饰电极在K3[Fe(CN)6]溶液中的电化学行为.CV显示球磨5 h碳纳米管修饰电极的氧化峰电流Ipa为18.53 μA,比没有球磨的碳纳米管修饰电极的氧化峰电流Ipa(12.50 μA)增大约50%.EIS谱图显示球磨后的MWNTs更能有效地促进Fe(CN)63-的扩散和电子转移,具有更高的电化学活性.     

碳糊电极阳极吸附伏安法测定双酚A

报道了用碳糊电极阳极吸附伏安法测定双酚A的方法。在Na2HPO4-NaH2PO4(pH 7.0)缓冲液中,双酚A在碳糊电极(CPE)上有一灵敏的吸附氧化峰,峰电位为0.63 V(vs.SCE)。该氧化峰的二阶导数峰电流与双酚A的浓度在2.0×10-8~8.0×10-6mol/L(富集90 s)范围内呈良好的线性关系,相关系数为0.9963,检出限为1.0×10-8mol/L(S/N=3,富集110 s),探讨了双酚A在碳糊电极上的伏安性质和电极反应机理,并且成功应用于聚碳酸酯塑料中双酚A含量的测定与其加入回收率实验。     

核黄素(VB2)在液体石蜡碳糊电极上的伏安特性及脉冲伏安法测定

以液体石腊碳糊电极为工作电极,在0.1 mol/L NaCl(pH=2.5)底液中研究VB2的伏安特性.VB2有一对氧化还原峰,峰电位为氧化峰(I)-110 mV/还原峰(Ⅱ)-160 mV,结果表明溶液中VB2的电极过程主要受VB2表面吸附控制.VB2溶液受光照后,增加一对光色素的氧化还原峰,其峰电位为氧化峰(Ⅳ)-220mV/还原峰(Ⅲ)-280 mV.采用微分脉冲伏安法进行VB2的定量分析,线性范围为1×10-5～6.0×10-8moL/L,检测下限为2.00×10-8moL/L.测定复合VB药片中的VB2,RSD为2.1%,回收率为96.8～104%,其结果与药典中标准方法测定结果一致.     

Layer-by-layer construction of multi-walled carbon nanotubes, zinc oxide, and gold nanoparticles integrated composite electrode for nitrite detection

A novel composite electrode of Au/ZnO/MWCNTs/GC has been constructed for the electrochemical detection of nitrite, where ZnO thin film and Au nanoparticles are electrodeposited through layer-by-layer onto MWCNTs/GC substrate. The resulting electrode is characterized by scanning electron microscopy and energy-dispersed X-ray spectroscopy. Its electrocatalytic activity toward the electro-oxidation of nitrite has been examined and compared to various modified electrodes, including MWCNTs/GC, Au/ZnO/GC, Au/MWCNTs/GC, and ZnO/MWCNTs/GC via cyclic voltammetry. The electrodeposition time for ZnO and the Au loading amount together with the solution pH are investigated to achieve optimal conditions for the electrode fabrication and nitrite detection. Linear relationship between current response and nitrite concentration is observed in the range from 7.8 × 10⁻⁷ to 4.0 × 10⁻⁴ M and the limit of the detection is 4.0 × 10⁻⁷ M (S/N = 3). The influence of various anions and cations on the nitrite detection has been studied. The proposed method is also employed for the determination of nitrite in real samples.     

In situ fabricated iodine-adlayer assisted selective electrooxidation of uric acid in alkaline media

This work presents the electrooxidation of uric acid (UA) at an iodine-adlayer-modified gold, Au (I|Au (poly)) electrode in 0.1 M NaOH solution using cyclic voltammetric, amperometric and open-circuit potential measurement techniques. A tremendous enhancement of the electrode activity towards the electrooxidation of UA was achieved by virtue of the simple modification of the Au (poly) electrode surface with a neutral iodine-adlayer, fabricated in situ through the spontaneous oxidative chemisorption of iodide present in the sample solution. The cyclic voltammetric peak current increases remarkably for the oxidation of UA and the peak potential shifts by 365 mV to the negative direction of potential compared to the bare Au (poly) electrode. Oxidation of ascorbic acid (AA) at the I|Au (poly) electrode takes place at the same potential as that at the bare electrode, but the peak current intensity is almost twice at the bare Au (poly) electrode as compared to the modified one. In the mixture of the AA and UA, the cyclic voltammetric signals corresponding to the oxidations of AA and UA were resolved by 340 mV. The electrode response in the mixture was highly reproducible because of the inhibition of adsorption of oxidation products and UA.     

Electrochemical preparation of pyronin Y thin films on gold substrates

Cyclic voltammetry, chronoamperometry, UV‐vis absorption spectroscopy, fluorescence spectroscopy, FTIR spectroscopy, and AFM techniques have been employed to investigate pyronin Y thin films formed on Au(111) substrates by electrochemical oxidation of pyronin Y monomer. The medium used in the electropolymerization was an anhydrous acetonitrile solution containing 0.1M TBAClO₄ as supporting electrolyte. Anodic electropolymerization potential (1450 mV) of pyronin Y has been obtained from cyclic voltammetry data. Solid‐state electropolymerization of pyronin Y was performed by the potential‐controlled electrolysis technique. Chronoamperometry studies indicate that the adsorption of pyronin Y takes place in an instantaneous three‐dimensional nucleation and growth mechanism which is accompanied by random adsorption. UV‐vis absorption and fluorescence spectra of the electrolysis solution as a function of electrodeposition time show the adsorption of insoluble pyronin Y films on Au electrode surface. FTIR‐specular reflectance of a polymer coated Au electrode reveals that there is a possible C? C coupling in the formation of polymeric pyronin Y structure. A well ordered polymeric chain structure of pyronin Y on Au(111) has been observed from AFM data. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hydrothermal process synthesized electrocatalytic multi-walled carbon nanotubes-inserted gold composite microparticles toward ethanol oxidation reaction

Composite microparticles consisting of large gold (Au) particles embedded with multi-walled carbon nanotubes (MWCNTs), denoted as MWCNTs-Au, have been successfully prepared by a facile hydrothermal process of gold(III) chloride (AuCl₃) in a MWCNT aqueous solution. X-ray diffraction and scanning electron microscopy reveal that the obtained Au particles have an average diameter of about 500 nm and some MWCNTs are inserted into the Au particles. The MWCNTs-Au composites in the ethanol oxidation reaction (EOR) show quite different shape of cyclic voltammograms (CVs) toward EOR when compared to the previous CV reports on the pure Au substrate.     

Electrocatalytic oxidation of ascorbic acid using a single layer of gold nanoparticles immobilized on 1,6-hexanedithiol modified gold electrode

This paper describes the electrocatalytic oxidation of ascorbic acid (AA) in phosphate buffer solution by the immobilized citrate capped gold nanoparticles (AuNPs) on 1,6-hexanedithiol (HDT) modified Au electrode. X-ray photoelectron spectrum (XPS) of HDT suggests that it forms a monolayer on Au surface through one of the two SH groups and the other SH group is pointing away from the electrode surface. The free SH groups of HDT were used to covalently attach colloidal AuNPs. The covalent attachment of AuNPs on HDT monolayer was confirmed from the observed characteristic carboxylate ion stretching modes of citrate attached with AuNPs in the infra-red reflection absorption spectrum (IRRAS) in addition to a higher reductive desorption charges obtained for AuNPs immobilized on HDT modified Au (Au/HDT/AuNPs) electrode in 0.1 M KOH when compared to HDT modified Au (Au/HDT) electrode. The electron transfer reaction of [Fe(CN)₆]^4−/3− was markedly hindered at the HDT modified Au (Au/HDT) electrode while it was restored with a peak separation of 74 mV after the immobilization of AuNPs on Au/HDT (Au/HDT/AuNPs) electrode indicating a good electronic communication between the immobilized AuNPs and the underlying bulk Au electrode through a HDT monolayer. The Cottrell slope obtained from the potential-step chronoamperometric measurements for the reduction of ferricyanide at Au/HDT/AuNPs was higher than that of bare Au electrode indicating the increased effective surface area of AuNPs modified electrode. The Au/HDT/AuNPs electrode exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA) by enhancing the oxidation peak current to more than two times with a 210 mV negative shift in the oxidation potential when compared to a bare Au electrode. The standard heterogeneous electron transfer rate constant (k_s) calculated for AA oxidation at Au/HDT/AuNPs electrode was 5.4 × 10⁻³ cm s⁻¹. The oxidation peak of AA at Au/HDT/AuNPs electrode was highly stable upon repeated potential cycling. Linear calibration plot was obtained for AA over the concentration range of 1–110 μM with a correlation coefficient of 0.9950. The detection limit of AA was found to be 1 μM. The common physiological interferents such as glucose, oxalate ions and urea do not show any interference within the detection limit of AA. The selectivity of the AuNPs modified electrode was illustrated by the determination of AA in the presence of uric acid.     

A remarkable activity of glycerol electrooxidation on gold in alkaline medium

In this paper, the activity and stability of glycerol oxidation on Au electrode have been investigated by cyclic voltametry, chronoamperometry and chronopotentiometry methods in alkaline medium. The glycerol shows a remarkable activity and better performance than methanol, ethanol, n-propanol, isopropanol and ethylene glycol on the Au electrode in alkaline medium. The activity and stability of glycerol oxidation on the Au electrode are higher than that of glycerol oxidation on Pd electrode. The stability of glycerol oxidation on the Au electrode is higher than that of methanol and glycerol oxidation on Pt electrode. The results show that glycerol is an excellent fuel applied in direct alcohol fuel cells with Au as anode catalyst.     

Modification of well-aligned carbon nanotubes with dihexadecyl hydrogen phosphate: application to highly sensitive nanomolar detection of simvastatin

The first usage of dihexadecyl hydrogen phosphate (DHP)-modified highly oriented multi-walled carbon nanotube (MWCNTs) forests in a sensor configuration was developed to investigate the electrochemical oxidation and determination of simvastatin (SV) in pharmaceutical dosage forms. Synthesis of well-aligned MWCNTs on a conductive Ta substrate by catalytic vapor deposition technique using a common chemical, ethylenediamine, and without being plasma-aided was reported. The electrochemical behavior and oxidation of SV at the aligned MWCNTs/DHP/Ta electrode were discussed in detail through cyclic voltammetry and differential pulse voltammetry. This modified electrode showed considerably higher electrocatalytic activity for SV than bare Ta electrode or entangled MWCNTs powder electrode, due to presence of the alignment and mutual separation of CNTs. Under the optimal conditions, the A-MWCNTs/DHP/Ta-modified electrode showed a wide linear range from 0.01 to 1 μM with a detection limit of 0.01 nM demonstrating promising results for the future usage in clinical applications.     

The role of multiwalled carbon nanotubes in enhancing the catalytic activity of cobalt tetraaminophthalocyanine for oxidation of conjugated dyes

Multiwalled carbon nanotubes (MWCNTs) used to support a metallophthalocyanine catalyst (CoTAPc-MWCNTs) were prepared using covalent immobilization of cobalt tetraaminophthalocyanine (CoTAPc) on them, and characterized by X-ray photoelectron spectroscopy, attenuated total reflection Fourier transform infrared spectra and thermogravimetric analysis. The oxidative decoloration of rhodamine 6G (Rh6G) in the presence of CoTAPc-MWCNTs and H₂O₂ was investigated by examination of UV-Vis absorption spectra. The results showed that Rh6G was oxidized efficiently in the CoTAPc-MWCNTs/H₂O₂ system. The introduction of MWCNTs resulted in a marked enhanced catalytic activity that CoTAPc does not have. Electron paramagnetic resonance spin-trap experiments indicated that CoTAPc-MWCNTs have a novel non-radical pathway, which is different from common CoTAPc catalytic systems. Furthermore, the result of online electrochemical measurement in the CoTAPc-MWCNTs/H₂O₂ system suggested that MWCNTs might participate directly in the electron transfer process in the catalytic oxidation of this conjugated dye. In this catalytic system, MWCNTs provide strong adsorption to conjugated Rh6G due to their special sp²-hybridized surface, and are able to rapidly oxidize the conjugated dye by a special electron transfer pathway.     

Adsorption of asparagine on the gold electrode and air/solution interface

The adsorption of asparagine (Asn) on a gold electrode from 0.1 M LiClO₄ aqueous solutions was investigated. The experimental data obtained from ac impedance measurements were analyzed to determine the dependence of adsorption parameters, i.e. the standard Gibbs energy of adsorption (ΔG⁰), maximal value of surface excess concentration (Γ_max) of Asn and parameter of interactions in the adsorbed layer (A) on the electrode potential. The relatively large value of Gibbs energy of adsorption (∼ −47 kJ mol⁻¹) gives the evidence of a very strong adsorption of Asn at the polycrystalline Au electrode. The comparison of the adsorption behavior of Asn at the air/solution and the Au/solution interfaces points out to the significant electronic interactions of adsorbate molecules with the Au electrode, since the adsorption of Asn on a free surface (from the same solutions) is very week. The analysis of the electrochemical data as well as the infrared reflection absorption spectroscopy (IRAS) results reveal that Asn molecules are anchored to the Au surface through oxygen atoms of the carboxylate group COO⁻ and through the amide carbonyl group.     

Electrooxidation of methanol and ethylene glycol on gold and on gold modified with an electrodeposited polyNiTSPc film

The electrooxidation of methanol and ethylene glycol on Au and on polynickeltetrasulphophthalocyanine-modified gold (polyNiTSPc/Au/Q) electrodes in a pH 11 carbonate/hydrogen carbonate buffer electrolyte was studied by cyclic voltammetry (CV) and with an electrochemical quartz crystal microbalance (EQCM). Au shows negligible activity for methanol oxidation, in agreement with the fact that methanol does not adsorb on Au, since it does not affect the potential at which the mass increase due to Au oxidation starts. On the contrary, ethylene glycol (EG) is electrooxidized on Au at a significant rate, probably because it adsorbs rather strongly on Au, as evidenced by the positive shift by 0.35 V of the mass increase attending Au monolayer oxidation. The polyNiTSPc-modified Au electrodes are hydrophobic, as inferred from the disappearance of the large mass decrease in the double-layer region typical of the bare Au electrode, a decrease which is due to the desorption of the water molecules adsorbed at the negative potential limit. On the polyNiTSPc/Au/Q electrodes the current at the positive potential limit (at which only Ni(III) exists) of methanol oxidation, and the peak current of EG oxidation (at a potential at which only Ni(II) exists), show a Langmuir dependence on the concentration, which indicates that in both cases the reactive species are adsorbed, and that their oxidation rate is much lower than the adsorption rate. As is well known, the oxidation of Ni(II) to Ni(III) in the polyNiTSPc film is accompanied by a large mass decrease, due mostly to the expulsion of water from the film by the hydrophobic Ni(III). This mass decrease is independent of the scan rate, but in the presence of methanol or ethylene glycol it increases with increasing scan rate, which indicates that the oxidation of the alcohols involves a chemical reaction of the alcohols with Ni(III) ions, the extent of which decreases with increasing rate. Consequently, the amount of the hydrophobic Ni(III) will increase, and so will the mass loss. The mass decrease of Ni(II) oxidation decreases with increasing concentration of methanol or ethylene glycol, which again shows that there is a chemical reaction between the alcohols and Ni(III) ions, since the concentration of the latter would decrease with increasing alcohol concentration.