A Study of Preparation and Performance of a Dichlorvos Electrochemical Sensor Based on Molecularly Imprinted Technique

A new dichlorvos molecularly imprinted electrochemical sensor was prepared. The sensitive membrane sensor was fabricated by electro-polymerizing on an Au electrode surface using o-aminophenol as a monomer and dichlorvos as a template. The 5 mmol/L K₃[Fe(CN)₆] containing 0.1 mol/L KCl was used as the test background solution, while cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to study the properties of the senor. The changes of oxidation peak current versus dichlorvos concentration showed linearity in the range of 0.12–0.42 µmol/L (R ² = 0.9432) and 0.45–15 µmol/L (R ² = 0.9516) with a detection limit of 0.06 µmol/L (S/N = 3). Moreover, the selectivity and repeatability properties of the dichlorvos electrochemical sensor were examined. Results showed that the senor had excellent repeatability (RSD = 3.92%, n = 5), good selectivity to the dichlorvos in detection, and only a ten minute response time. Organophosphorus insecticides have some response signals in the detections.     

Determination of Oxytetracycline with a Gold Electrode Modified by Chitosan-Multiwalled Carbon Nanotube Multilayer Films and Gold Nanoparticles

A molecularly imprinted electrochemical sensor was fabricated based on a gold electrode modified by chitosan-multiwalled carbon nanotube composite (CS-MWCNTs) multilayer films and gold nanoparticles (AuNPs) for convenient and sensitive determination of oxytetracycline (OTC). The multilayer of CS-MWCNTs composites and AuNPs were used to augment electronic transmission and sensitivity. The molecularly imprinted polymers (MIPs) were synthesized using OTC as the template molecule and o-phenylenediamine (OPD) as the functional monomer. They were modified on a gold electrode by electropolymerization. The electrochemical behavior of OTC at the imprinted sensor was characterized by cyclic voltammetry (CV), scanning electron microscopy (SEM), and amperometry. The molecularly imprinted sensor showed high selectivity and excellent stability toward OTC. The linear range was from 3.0 × 10^?8 to 8.0 × 10^?5 mol/L, with a limit of detection (LOD) of 2.7 × 10^?8 mol/L (S/N = 3). The developed sensor showed good recovery in spiked samples analysis.     

Chalcopyrite and pyrite floatabilities in the presence of sodium sulfide and sodium metabisulfite in a high pyritic copper complex ore

One of the principal problems in flotation of copper complex ores is the presence of pyrite and copper-activated pyrite in moderately alkaline pHs. Misreported pyrite into copper concentrates dramatically declines copper grade and its recovery. In this study, the effect of sodium sulfide, sodium metabisulfite (SMBS), and their dosages (100, 200, 300, and 400 g/t) were investigated on chalcopyrite and pyrite floatabilities in a high pyritic copper sulfide ore. Furthermore, the role of particle size distribution (PSD) in three different levels (i.e., d₇₀, d₇₅, and d₈₀ of passing 75 µm) was evaluated by a series of batch flotation experiments. It was revealed that using 200 g/t SMBS provides not only the highest and the lowest chalcopyrite and pyrite recoveries, but also the maximum and minimum copper and iron grades. Pyrite recovery was sharply increased by the addition of sodium sulfide in light of sodium sulfide-induced collectorless flotation; however, it showed a very weak effect on chalcopyrite floatability. In addition, the highest and lowest chalcopyrite and pyrite recoveries were, respectively, identified when d₇₅ equaled to 70% 75 µm. In other words, for the high pyritic copper ore type, it is feasible to achieve the highest chalcopyrite recovery consuming the lowest grinding energy.     

A chemical, morphological, and electrochemical (XPS, SEM/EDX, CV, and EIS) analysis of electrochemically modified electrode surfaces of natural chalcopyrite (CuFeS2) and pyrite (FeS2) in alkaline solutions

Electrodic surfaces of natural chalcopyrite and natural pyrite minerals (El Teniente mine, Chile) have been studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy including microanalysis (SEM/EDX). For comparison, fractured and polished mineral surfaces were also studied by XPS. In both electrodes, the formation of Fe(III) species containing oxygen were detected and Cu(II) species containing oxygen were additionally detected for chalcopyrite at advanced oxidation states. The presence of Cu(II) species containing oxygen was not detected by XPS for the initial oxidation states of the chalcopyrite. For pyrite, the present results do not allow confirmation of the presence of polysulfurs such as have been previously proposed. In both minerals, the measurements of SEM and EDX show relevant alterations in the respective surfaces when different potential values were applied. The chalcopyrite surface shows the formation of protrusions with a high concentration of oxygen. The pyrite surface shows a layer of modified material with high oxygen content. The modifications detected by XPS, SEM, and EDX allowed the explanation of the complexity of the equivalent circuit used to simulate the experimental EIS data. At high oxidation states, both minerals showed a pseudoinductive loop in the equivalent circuit, which was due to the active electrodissolution of the minerals which takes place through a surface film previously formed.     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

银在浸出黄铜矿中的催化作用

本文研究了用Fe_2(SO_4)_3、MnO_2、FeCl_3、CuCl_2等浸出黄铜矿时Ag~ 的作用。Ag~ 在氯化物溶液中不起催化作用。但在酸性Fe_2(SO_4)_3及MnO_2溶液中可使反应速率常数提高200倍,文中导出了在Ag~ 催化作用下硫酸高铁浸出黄铜矿的动力学方程。确定了速率控制步骤是离子通过产物硫层的扩散过程,活化能为35.7kJ/mol。探讨了银催化浸出黄铜矿的反应机理。     

A Uric Acid Biosensor Based on Langmuir-Blodgett Film as an Enzyme-Immobilizing Matrix

A uric acid biosensor was fabricated by the Langmuir–Blodgett (LB) technique to immobilize the uricase on chitosan/Prussian blue (CS/PB) prefunctionalized indium-tin oxide (ITO) electrode. The effects of ionic strengths, acidity of subphase, and uricase amount on the film were studied. The electrochemical properties of the uricase/n-nonadecanoic acid (UOx/NA) LB film proved that CS/PB was a good electro-catalyst for the reduction of hydrogen peroxide produced by enzymatic reaction of UOx, and protein molecules retained their natural electro-catalytic activity. The linear range of uric acid detection was from 5 × 10^?6 mol/L to 1.15 × 10^?3 mol/L with a detection limit of 1.8 × 10^?7 mol/L.     

Electrochemical characterization of fine-grained blast furnace sludge after acid leaching using carbon paste electrode

The paper deals with the study of electrochemical properties of blast furnace sludge after acid leaching (BFSL) using modified carbon paste electrodes (CPEs) in acidic (1 M HCl) and alkaline (1 M NaOH) electrolyte. A polyamide holder with exchangeable tips was developed. The effect of their geometric parameters on the electrochemical response was monitored. The electrochemical characterization was performed by cyclic voltammetry (CV) at different scan rates. The hematite and magnetite served as comparative model modifiers. The identification of reaction products was performed using the RTG diffraction and SEM/EDX analyses. It was found that reduction reactions are suppressed at acidic pH. On the contrary, in an alkaline media, a significant peak corresponding to the electrode reduction of iron oxides based on the scheme Fe³⁺?→?Fe²⁺?→?Fe⁰ was identified in the BFSL reduction region. XRD and SEM analyses of the active surface of modified CPE showed the formation of nanostructured Fe. The results provide direction for the further use of BFSL.     

Determination of Guanidino Compounds in Serum by Micellar Electrokinetic Capillary Chromatography Using Benzoin as the Derivatizing Reagent

An analytical procedure has been evolved for the determination of seven guanidino compounds; guanidine (G), methylguanidine (MG), guanidinoacetic acid (GAA), guanidinopropionic acid (GPA), guanidinobutyric acid (GBA), arginine (Arg), and guanidinosuccinic acid (GSA) by micellar electrokinetic capillary chromatography (MEKC) within 6 min using benzoin as derivatizing reagent. Sodium dodecyl sulfate (SDS) was used as the micellar medium in a sodium tetraborate (0.1 M) buffer at pH 8.5. Uncoated fused silica capillary was used with an effective length of 39 cm and 75 μm id. Applied voltage was 25 kV and photo diode array detection was set at 228 nm. Linear calibrations obtained from 0.057 to 14.11 μmol/L and limits of detection (LOD) were within 0.019–0.03 μmol/L. The derivatization and separation was repeatable with relative standard deviation (RSD) within 1.9–3.8%. Serum of healthy volunteers and uremic patients was analyzed and amounts found in uremic patients were G 1.98–3.03, MG 1.21–1.79, GAA 3.67–6.09, GPA 1.17–1.37, GBA 1.29–1.46, Arg 9.49–19.17, and GSA 6.83–10.91 μmol/L with RSD (n = 4) within 1.3–4.5%. The amount of guanidino compounds was higher in uremic patients than in healthy volunteers.     

Oxidation of sulphide minerals--I: determination of ferrous and ferric iron in samples of pyrrhotite, pyrite and chalcopyrite

A method has been developed for determining small amounts of both ferrous and ferric iron in oxidized samples of pyrrhotite, pyrite and chalcopyrite. The oxidized iron is selectively dissolved in 10M phosphoric acid under reflux and can be determined with the accuracy generally accepted in chemical phase analysis.     

纳米多孔二氧化钛电极辅助光电化学降解乙酰氨基酚及伐昔洛韦

作为一类具有较高生物活性的物质,药物及个人护理品对环境的污染引起人们越来越多的关注.对乙酰氨基酚和伐昔洛韦是两种使用广泛的药物,由于其潜在的对人类健康和生态安全的威胁而逐渐成为研究热点.而电化学辅助光氧化技术因其具备能够高效处理难降解化学品的优点而得到广泛使用.本文合成了纳米多孔二氧化钛电极,研究了电化学还原处理对纳米多孔二氧化钛电极辅助光电化学降解对乙酰氨基酚和伐昔洛韦的影响.使用扫描电镜和色散谱技术对合成的纳米多孔二氧化钛电极的形态和元素组成进行了表征.循环伏安法、莫特-肖特基曲线、紫外-可见分光光度计和总有机碳分析仪被用来研究对乙酰氨基酚和伐昔洛韦的光电化学降解过程.结果显示,对乙酰氨基酚和伐昔洛韦的光化学降解和电化学降解过程非常缓慢,在研究的时间范围内其浓度未见明显变化,因此可以忽略不计.但是对乙酰氨基酚和伐昔洛韦的光电化学降解速度比较快,与未经处理的纳米多孔二氧化钛电极相比,经过电化学还原处理的电极可以使对乙酰氨基酚和伐昔洛韦的光电化学降解分别提高86.96%和53.12%.这可能是由于在电化学还原处理过程中生成了Ti3+, Ti2+和氧空位以及导电性的提高.还研究了温度对对乙酰氨基酚和伐昔洛韦光电化学降解的影响,随着温度升高,对乙酰氨基酚和伐昔洛韦的光电化学降解速率增大.     

Li_2CO_3添加剂对石墨电极性能的影响

运用电化学阻抗谱(EIS)和循环伏安法(CV)研究了在1mol/LLiPF6-EC(碳酸乙烯酯):DMC(碳酸二甲酯)电解液中添加Li2CO3对石墨电极性能的影响及机制.CV研究结果表明,在1mol/LLiPF6-EC:DMC电解液中添加Li2CO3能够有效抑制石墨电极首次充放电过程中碳酸乙烯酯(EC)的单电子还原过程,即还原分解产生乙烯和碳酸锂的过程,进而改善石墨电极的电化学循环性能.EIS研究结果表明,在添加Li2CO3的1mol/LLiPF6-EC:DMC电解液中,石墨电极表面的固体电解质相界面膜(SEI膜)具有较强的黏弹性,可以更好地适应锂离子嵌入过程中石墨颗粒体积的微小变化,从而使锂离子的嵌入过程更容易进行.     

A new sensor architecture based on carbon Printex 6L to the electrochemical determination of ranitidine

A glassy carbon electrode (GCE) modified with carbon Printex 6L (Printex6L/GCE) as a novel sensor is proposed. A morphological study was carried out using scanning electron microscopy, and an electrochemical characterization of the proposed electrode was performed by cyclic voltammetry (CV) using [Fe(CN)₆]^4? as a redox probe. With the incorporation of the carbon Printex 6L film onto the GCE surface, the [Fe(CN)₆]^4? analytical signal was substantially increased and the difference between the oxidation and reduction potentials (ΔE _p) decreased, a characteristic of the electrocatalytic effect. Furthermore, the use of carbon Printex 6L film resulted in an 84 % increase in the oxidation current and a 123 % increase in the reduction current. Faster charge transfer was observed at the proposed electrode/electrolyte interface during CV when compared with GCE. The Printex6L/GCE was tested for ranitidine (RNT) sensing and showed a decrease in the working potential and an increase in the analytical signal, when compared with GCE, again demonstrating an electrocatalytic effect. Under optimized experimental conditions, the developed square-wave adsorptive anodic stripping voltammetry (SWAdASV) method presented an analytical curve that was linear in RNT concentration range from 1.98 × 10^?6 to 2.88 × 10^?5 mol L^?1 with a detection limit of 2.44 × 10^?7 mol L^?1. The developed Printex6L/GCE was successfully applied to the determination of RNT concentrations in human body fluid samples (urine and serum).     

Fabrication of high-performance supercapacitors based on hollow SnO2 microspheres

Hollow SnO₂ microspheres are prepared from resorcinol–formaldehyde gel and different tin compound precursors, including stannous sulfate (SnSO₄), stannous chloride dihydrate (SnCl₂·2H₂O), and stannic chloride pentahydrate (SnCl₄·5H₂O) via chemically induced self-assembly in hydrothermal environment. Morphological and structural characterizations of as-prepared hollow SnO₂ microspheres are carried out using scanning electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption method. Their electrochemical properties as the supercapacitor electrode materials for application are also investigated using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurement in 1 M H₂SO₄ electrolyte. There are redox peaks in CV curves and a large number of Faradic plateaus in GCD curves. At different scan rates, all the obtained samples have excellent electrochemical properties. The hollow SnO₂ microspheres obtained from SnSO₄ and SnCl₂·2H₂O as precursors show relatively lower specific capacitances of 395 and 347 F g^?1, respectively. However, the specific capacitance of SnO₂ from SnCl₄·5H₂O is up to 663 F g^?1. The high specific surface area and hollow structure of SnO₂ microspheres are due to facilitating the rapid transport of electrolyte ions and improving the electrochemical performance. It is expected that hollow SnO₂ microspheres are the promising redox supercapacitor materials.     

Electrochemical Behavior of Hydrogen Peroxide at a Glassy Carbon Electrode Modified with Nickel Hydroxide–Decorated Multiwalled Carbon Nanotubes

Abstract

The multiwalled carbon nanotube–nickel hydroxide composite film used to modify glassy carbon electrode was prepared and confirmed by transmission electron microscopy and cyclic voltammetry. The process and mechanism of film formation were discussed in detail. The electrode modified with the composite film exhibited good catalytic activity toward electrochemical oxidation of hydrogen peroxide in 0.1 mol/L sodium hydroxide solution. Various factors affecting the electrocatalytic activity of nickel hydroxide film were investigated. The anodic peak current increased with the increased concentration of hydrogen peroxide. The linear range for the determination of hydrogen peroxide was from 1.5 × 10^?6 mol/L to 2.5 × 10^?3 mol/L with the detection limit 6.1 × 10^?7 mol/L (S/N = 3). And the proposed method was applied to the determination of hydrogen peroxide in disinfector with higher sensitivity and lower detection limit.     

Electrochemical Determination of Phenylethanolamine A Based on Nafion/MWCNTs/AuNPs Modified Carbon Electrode

Phenylethanolamine A (PEA), a β‐agonist, was found to be illegally used as a growth promoter in pigs last year, causing Chinese government's great attention. Here, a sensitive electrochemical method was developed for detecting PEA by immobilization of gold nanoparticles (AuNPs), multiwalled carbon nanotubes (MWCNTs) and Nafion on the surface of a glassy carbon electrode (GCE). The Nafion/MWCNTs/AuNPs film was characterized by scanning electronic micrographs (SEM) and electrochemical impedance spectroscopy (EIS). The electrochemical behaviors of PEA at the modified GCE were investigated in detail. The synergetic effects of AuNPs, MWCNTs and Nafion amplify the electrochemical reduction signal of PEA, and result in high sensitivity for PEA determination. Under the optimal conditions, the electrochemical sensor shows a wide linear range of 0.01 to 10 (mol/L with a detection limit of 0.005 µmol/L. Moreover, the fabricated sensor presents high selectivity and long‐term stability, which paves a new way for simple, rapid, sensitive detection of PEA.     

Mercury meniscus on solid silver amalgam electrode as a sensitive electrochemical sensor for tetrachlorvinphos

The in-house prepared mercury meniscus modified solid silver amalgam electrode (m-AgSAE) was successfully applied for the detection of organophosphate pesticide tetrachlorvinphos in pH 7 buffer solution. The electrochemical performance of m-AgSAE for the reduction of tetrachlorvinphos was evaluated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and square wave voltammetry (SWV), respectively. The surface morphology of solid silver electrode (AgE), as-amalgamated solid silver amalgam electrode (AgSAE), and polished solid silver amalgam electrode (p-AgSAE) was examined by field emission scanning electron microscopy (FESEM). Among the applied techniques, DPV and SWV analysis showed a remarkable increase in the reduction peak current and provided a simple, fast, and sensitive method for the determination of tetrachlorvinphos. The electrochemical impedance spectroscopy (EIS) was used to correlate the electrocatalytic activity of AgSAE, p-AgSAE and m-AgSAE with their interfacial charge transport capabilities. Under the optimized experimental conditions, the DPV and SWV responses were linear over the 1–9 μM and 10–50 μM concentration ranges with a detection limit of 0.06 μM for DPV and 0.04 for SWV. The estimation of tetrachlorvinphos in the ground and waste water samples with the proposed method was in good agreement with that of the added amount. The proposed electrochemical method not only extends the application of non-toxic m-AgSAE, but also offers new possibilities for fast and sensitive analysis of tetrachlorvinphos and its structural analogs in environmental samples.     

Electrochemical determination of picric acid based on platinum nanoparticles–reduced graphene oxide composite

Platinum nanoparticles–reduced graphene oxide composite-modified glassy carbon electrode (PtNPs–rGO/GCE) was developed as a simple, selective and sensitive electrochemical sensor for determination of picric acid (PA). Cyclic voltammogram (CV) of PA showed three well-defined irreversible reduction peaks at the potentials of ?0.43, ?0.57 and ?0.66 V versus Ag/AgCl. In this work, the interference effect of other nitrophenol compounds (NPhCs) was significantly reduced by appropriate adjusting of pH. Square wave voltammetry was used for quantification of PA in the range of 5–500 µM (1.15–115 mg L^?1) with practical detection limit of 1 µM (0.23 mg L^?1). The proposed sensor was successfully applied for the determination of PA in two natural water samples.     

Effect of storage time on the pressure oxidation enthalpy of pyrite

The information on heat of oxidation?Creduction reactions is important for the heat balance and optimization of the autoclave design in the hydrometallurgical industry in ore processing. Pyrite (FeS₂) is a gangue mineral that presents with nickel-containing pentlandite, and copper-containing chalcopyrite minerals. The presence of pyrite impacts to the overall heat of leaching process. This study has been performed on a differential scanning calorimeter (DSC80, Setaram) with a commercial mixing cell to study the thermal behaviour of pure pyrite FeS₂ (Valdenegrillos, Spain) mineral particles during oxidative pressure leaching at 150?°C and partial oxygen pressure of 3.4?MPa. A calorimetric method for determining the enthalpy of leaching of sulphide minerals at high temperatures and oxygen pressures has been used to evaluate the enthalpies of oxidation of freshly ground pyrite and pyrite stored for a year in contact with air (stored pyrite) under conditions relevant to pressure oxidation operations. Ground pyrite stored over time has long since been known to result in greater heat evolution during oxidative leaching. A likely mechanism for this phenomenon was uncovered: formation of ferrous sulphate and sulphuric acid during storage in contact with air influencing greater heat evolution at the outset of the reaction. Two mass loss steps on TG curve of stored pyrite, attributed to the elimination of atmospheric moisture and H₂O molecule from FeSO₄·H₂O, is absent on TG curve of freshly ground pyrite.     

Poly(aminohippuric acid)–sodium dodecyl sulfate/functionalized graphene oxide nanocomposite for amplified electrochemical sensing of gallic acid

Gallic acid (GA), as a main phenolic acid, has been considered the main player on the human health, including the effects of reduction of cholesterol, depression of hypertension, anti-oxidation, anti-microbial, protection against cardiovascular disease and cancer. This study describes the development, electrochemical characterization and utilization of a novel functionalized graphene oxide/poly(p-aminohippuric acid)–sodium dodecyl sulfate nanocomposite modified glassy carbon electrode (APTS@GO/PPAH-SDS/GCE) for the electrocatalytic determination of GA. The synthesized nanocomposite was characterized by different techniques such as Fourier-transform infrared spectroscopy, thermo-gravimetric analysis and transmission electron microscopy. The electrochemical oxidation of GA was investigated by cyclic voltammetry, differential pulse voltammetry and amperometry. The modified electrode showed a potent and persistent electron mediating behavior followed by well-defined oxidation peak of GA and the linear range of 0.006–2000 µmol L^?1 with a detection limit of 1.7 nmol L^?1 for GA (S/N?=?3) using amperometric method. Also, it was successfully used for the GA determination in the black tea and tab water as real samples. Additionally, this electrode exhibited good stability and reproducibility. The results imply that the APTS@GO/PPAH-SDS nanocomposite might be a promising candidate for practical applications in GA electrochemical detection.