A Metal‐Free Approach Based on Graphene Oxide‐Modified Electrode for Monitoring the Photoelectrocatalytic Degradation of EDTA

A novel voltammetric method for the sensitive determination of ethylenediaminetetraacetic acid (EDTA) was developed based on a graphene oxide (GO) modified electrode. In acetate buffer solution, GO showed a voltammetric response composed of a sharp anodic peak and a weak cathodic peak. When EDTA was present in the solution, the voltammetric response of GO was suppressed. Under optimum conditions, the response of the GO‐modified electrode was inversely proportional to the concentration of EDTA from 6.0×10^?7 to 1.0×10^?4 mol/L. Using such a GO‐based voltammetry, the effective photoelectrocatalytic degradation of EDTA over a TiO₂ film electrode was evaluated and some influencing factors were investigated.     

CdSe/泡沫镍薄膜电极对结晶紫的光电催化降解

采用恒电位电沉积法,以泡沫镍为基底电极,制备了CdSe/泡沫镍薄膜电极,采用扫描电子显微镜、紫外可见漫反射光谱和能谱分析表征了CdSe薄膜的形貌及其组成。应用该电极研究结晶紫溶液在光电催化降解过程中的COD去除率。结果表明,以白炽灯(100 W,2只)为光源,采用电沉积30 min所得的CdSe/泡沫镍薄膜电极为工作电极,外加偏压为0.4 V(vs.SCE),0.01 mol/L NaCl为电解质,光电催化降解浓度为0.001 g/L的结晶紫溶液120 min,COD去除率达到84.3%。     

One‐Pot Synthesis of 4‐Substituted 3,4‐Dihydro‐3‐methoxyisocoumarins via Carboxylation of α‐Substituted 2‐Lithio‐β‐methoxystyrenes with Carbon Dioxide

A new type of isocoumarins (=1H‐isochromen‐1‐ones=1H‐2‐benzopyran‐1‐ones), 4‐substituted 3,4‐dihydro‐3‐methoxyisocoumarins 2 , can be obtained by a one‐pot process from α‐substituted 2‐bromo‐β‐methoxystyrenes 1 . Thus, lithium 2‐(1‐aryl(or methyl)‐2‐methoxyethenyl)benzoates are conveniently generated via the Br/Li exchange between 1 and BuLi, followed by the action of CO₂ on the resulting α‐substituted 2‐lithio‐β‐methoxystyrenes. Upon treating with concentrated HCl at room temperature, these lithium benzoates undergo lactonization to provide the desired 3,4‐dihydroisocoumarins 2 in relatively good yields.     

Electrochemical Polymerization of 3,4‐Ethylenedioxythiophene from Aqueous Solution Containing Hydroxypropyl‐β‐cyclodextrin and the Electrocatalytic Behavior of Modified Electrode Towards Oxidation of Sulfur Oxoanions and Nitrite

Poly(3,4‐ethylenedioxythiophene) (PEDOT) film was prepared on glassy carbon electrode from 0.1 M LiClO₄ aqueous solution containing 3,4‐ethylenedioxythiophene (EDOT) monomer and hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD), by multiple scan cyclic voltammetry. The effect of oxidation potentials on electropolymerization of EDOT was examined by chronoamperometry and cyclic voltammetric techniques. The results of potentiostatic experiments show that optimum potential range to obtain compact stable film was 0.9 to 1.05 V (vs. Ag/AgCl). At higher positive potential, i.e. above 1.05 V, polymer growth was hindered by passivation effect. The PEDOT film exhibited a strong absorption at 550 nm in the UV‐vis region and also a multicolor electrochromism in different buffer solutions (sky blue‐purple red). Cyclic voltammetric features of PEDOT‐coated electrode in pure supporting electrolyte suggested that charge transfer of the film resembles that of surface‐confined redox species. Finally, the electrocatalytic behavior of PEDOT‐modified electrode was tested towards oxidation of sulfur oxoanions and nitrite using cyclic voltammetry.     

Cetylpyridinium Chloride as a Regulator in Paper Separation of 2,4‐Dichlorophenol and 2,4,6‐Trichlorophenol in Water

2,4‐Dichlorophenol (2,4‐DCP) and 2,4,6‐trichlorophenol (2,4,6‐TCP) by the use of cetylpyridinium chloride (CPCl) as a regulator was studied for their separation by the paper capillary permeation adsorption (PCPA) separation technique. The effect of pH, the type of PCPA treatment, the concentration of cetylpyridinium chloride, and various inorganic salts on the separatability has been investigated. A nearly 100% separatability was obtained at pH values 5–11 and 5–11, respectively, for 2,4‐dichlorophenol and 2,4,6‐trichlorophenol when cetylpyridinium chloride was present. It was confirmed that 2,4‐dichlorophenol and 2,4,6‐trichlorophenol are separated by adsorption on the fiber surface as ion pairs at the pH. Addition of inorganic salts decreases the separatability.     

Electrochemical Detection of 2‐Naphthol at a Glassy Carbon Electrode Modified with Tosflex Film

In this study, a Tosflex (a perfluoro‐anion‐exchange membrane) modified glassy carbon electrode has been used to detect 2‐naphthalenol (2‐naphthol) in aqueous solutions in order to demonstrate the electroanalytical application of Tosflex. 2‐naphthol polymerizes upon electrochemical oxidation at a glassy carbon electrode; however, the current related to this oxidation is too small for analytical purpose at low concentration level. A Tosflex polymer modified glassy carbon electrode (TFGCE) was found of having capability to improve the detection limit because 2‐naphthol molecules deprotonated in basic solutions to form 2‐naphtholate anions that were accumulated to TFGCE by the anion‐exchange characteristic of Tosflex. The accumulated 2‐naphtholate anions were determined with the following differential pulse voltammetry. With 3 minutes accumulation at +0.05 V, the dependence of oxidation current versus concentration was linear from 8×10^?7 M to 1×10^?5 M with a regression coefficient of 0.999 and a detection limit of 2×10^?7 M. Unlike many other anion‐exchange polymer modified electrodes, the TFGCE is stable at highly basic condition.     

A Novel L‐Cysteine Electrochemical Sensor Using Sulfonated Graphene‐poly(3,4‐Ethylenedioxythiophene) Composite Film Decorated with Gold Nanoparticles

By exploiting the electrostatic interaction between positively charged 3,4‐ethylenedioxythiophene cation radicals and negatively charged sulfonated graphene (SG) sheets, we prepared a poly(3,4‐ethylenedioxythiophene)‐sulfonated graphene (SG‐PEDOT) composite film by a one‐step electrochemical process. The composite was further decorated with gold nanoparticles (AuNPs) and employed as an electrode material for the detection of L ‐cysteine (Cys). The SG‐PEDOT composite film is shown to provide a rough surface for the electrodeposition of AuNPs and to improve substrate accessibility and interaction with Cys. Moreover, the AuNPs‐decorated composite exhibits better electrocatalytic performance than that of a SG‐PEDOT composite only. Under optimum experimental conditions, the amperometric current of the sensor is linearly related to the concentration of Cys in the 0.1 to 382 µM range, and the detection limit is 0.02 µM (at S/N=3). The modified electrode displays favorable selectivity, good stability and high reproducibility. The method was successfully applied to the detection of Cys in spiked human urine.     

Ta/Al-Fe2O3薄膜电极的制备及其光电催化降解亚甲基蓝性能

采用简单的涂滴法制备出新型的Al、Ta 共掺杂的三元铁氧化物(Ta/Al-Fe₂O₃)可见光响应型光催化薄膜. 运用X射线光电子能谱(XPS)和紫外-可见(UV-Vis)光谱等手段对其进行了表征, 考察了其光电化学性能, 并研究了复合电极光电催化降解亚甲基蓝(MB)废水的反应性能. 由表面谱学分析可知, Ta 和Al 成功掺入Fe₂O₃中, Ta 会改变催化剂表面Al 和O的化学环境. 在可见光照射下的光电催化(PEC)反应中, Ta/Al-Fe₂O₃降解MB的反应速率约为Al-Fe₂O₃的2 倍, 光电催化共作用的效果优于单纯光催化作用(PC)和电催化(EC)作用的效果.结果表明, Ta掺杂有利于提高Ta/Al-Fe₂O₃薄膜的光电催化活性.     

Electrochemical Oxidation and Sensitive Determination of Acetaminophen in Pharmaceuticals at Poly(3,4‐ethylenedioxythiophene)‐Modified Screen‐Printed Electrodes

The current study reports electrocatalytic oxidation of acetaminophen at screen‐printed electrode (SPE) modified with electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film. Cyclic voltammetric studies show that the SPE/PEDOT electrode lowers overpotentials and improves electrochemical behavior of acetaminophen (ACAP) in aqueous buffer solutions, compared to the bare SPE. Excellent analytical features are achieved, including high sensitivity, low detection limit and satisfactory dynamic range, by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and flow‐injection amperometry (FIA) under optimized conditions. The proposed methods obtain satisfactory results in detection of acetaminophen in two commercial tablets.     

Development of a Creatinine Sensor Based on a Molecularly Imprinted Polymer‐Modified Sol‐Gel Film on Graphite Electrode

An electrochemical creatinine sensor based on a molecularly imprinted polymer (MIP)‐modified sol‐gel film on graphite electrode was developed. The surface coating of MIP over sol‐gel was advantageous to obtain a porous film with outwardly exposed MIP cavities for unhindered selective rebinding of creatinine from aqueous and biological samples. A fast differential pulse, cathodic stripping voltammetric response of creatinine can be obtained after being preanodized the sensor in neutral medium containing appropriate amount of creatinine at +1.8 V versus SCE for 120 s. A linear response over creatinine concentration in the range of 1.23 to 100 μg mL^?1 was exhibited with a detection limit of 0.37 μg mL^?1 (S/N=3).     

Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.     

Highly Sensitive and Selective Determination of Dopamine Based on Graphite Nanosheet‐Nafion Composite Film Modified Electrode

A graphite nanosheet (GNS)‐Nafion modified glassy carbon (GC) electrode was prepared and used for highly sensitive and selective determination of dopamine (DA). The GNS‐Nafion/GC electrode displayed excellent electrocatalytic activities towards DA and ascorbic acid (AA). The selective determination of DA was carried out successfully in the presence of AA by differential pulse voltammetry. High sensitivity (3.695 μA μM^?1) and low detection limit (0.02 μM, S/N=3) for the DA detection were obtained. These good properties can be attributed to a large amount of edge plane defects presented on GNSs and the charge‐exclusion and concentration features of Nafion.     

Graphite Micropowder Modified with 4‐Amino‐2,6‐diphenylphenol Supported on Basal Plane Pyrolytic Graphite Electrodes: Micro Sensing Platforms for the Indirect Electrochemical Detection of Δ9‐Tetrahydrocannabinol in Saliva

Graphite micropowder has been modified with 4‐amino‐2,6‐diphenylphenol immobilized onto a basal plane pyrolytic graphite electrode and explored for the indirect electrochemical sensing of Δ⁹‐tetrahydrocannabinol in artificial saliva. The protocol is based on the electrochemical formation of quinoneimine which specifically reacts with Δ⁹‐tetrahydrocannabinol resulting in the loss of the quinoneimine which can be monitored via voltammetry. It is demonstrated that Δ⁹‐tetrahydrocannabinol can be detected in artificial saliva over the micromolar range. Such a protocol may find application in screening for drug abuse.     

TiO2‐modified Carbon Paste Electrode as a Sensor for the Assay of Weak Organic Acids/Bases and Complex Matrix Samples

The construction, general performance characteristics and analytical application of a titanium dioxide–modified carbon paste electrode sensitive to hydrogen ions, based on incorporation of titanium dioxide in a carbon paste matrix, is described. The proposed electrochemical sensor exhibits a linear response in the pH range from 2 to 10, at 25 °C, with a sub‐Nernstian slope. The value of a slope is in a direct correlation with the electrode composition – the optimum content of a titanium dioxide in carbon paste is 30 %. Titanium dioxide‐modified carbon paste electrode shows fast response time and reproducibility, confirmed by different compounds determination in both, individual and complex material, namely, in synthetic and real samples. Besides, the electrode shows high selectivity in the presence of the alkali and the alkaline earth ions as Na⁺, K⁺, Ca²⁺ or Mg²⁺. The standard deviation of the investigated acids (acetic, oxalic, 5‐sulfosalicylic, p‐toluensulfonic acid, and amino acid‐glycine) and bases (N,N′‐diphenylguanidine and collidine) is less than 1.3 %. The obtained data are compared with those obtained by using a conventional glass pH‐electrode under the same experimental conditions and indicate a high correlation between them.     

Electrochemical Oxidation of ds‐DNA on Polypyrrole Nanofiber Modified Pencil Graphite Electrode

Preparation of a polypyrrole nanofiber (PPyNF) modified pencil graphite (PG) electrode and its usage in the electrochemical DNA biosensors was investigated. The electrodes (PPyNF/PG1 and PPyNF/PG2) were prepared from a solution containing 0.1 M pyrrole, 0.1 M Na₂CO₃ and 0.1 M LiCIO₄ by using potentiostatic and potentiodynamic methods. PPyNF/PG2 electrodes which were prepared by potentiostatic procedure showed higher responses for the oxidation of ds‐DNA than the PPyNF/PG1 electrodes prepared by potentiodynamic methods. Immobilization of the ds‐DNA on PG and PPyNF/PG surfaces was performed at a constant potential, +0.5 V, for 300 s in 0.5 M ABS (pH 4.8) containing 15 μg mL^?1 ds‐DNA and 20 mM LiCIO₄. The oxidation peak potentials of the ds‐DNA bases, guanine and adenine, were shifted to more cathodic values by using PPyNF/PG electrodes. The oxidation signal of the guanine base of ds‐DNA was decreased in the presence of methylene blue.     

Electrochemical Determination of the Herbicide Bentazone Using a Carbon Nanotube β‐Cyclodextrin Modified Electrode

An electrochemical sensor has been developed for the determination of the herbicide bentazone, based on a GC electrode modified by a combination of multiwalled carbon nanotubes (MWCNT) with β‐cyclodextrin (β‐CD) incorporated in a polyaniline film. The results indicate that the β‐CD/MWCNT modified GC electrode exhibits efficient electrocatalytic oxidation of bentazone with high sensitivity and stability. A cyclic voltammetric method to determine bentazone in phosphate buffer solution at pH 6.0, was developed, without any previous extraction, clean‐up, or derivatization steps, in the range of 10–80 µmol L^?1, with a detection limit of 1.6 µmol L^?1 in water. The results were compared with those obtained by an established HPLC technique. No statistically significant differences being found between both methods.     

Decomposition and Detection of Hydrogen Peroxide Using δ‐MnO2 Thin Film Electrode with Self‐Healing Property

A thin film of δ‐type MnO₂ grown cathodically has been investigated with respect to the ability toward anodic decomposition of H₂O₂ and durability. With polarization at less positive potentials than +0.4 V vs. Ag/AgCl, the film was dissolved exclusively as a result of reduction of Mn⁴⁺ sites in the oxide by H₂O₂ to soluble Mn²⁺. At +0.9 V, MnO₂ remained unchanged and decomposed H₂O₂ in solution. At +0.8 V, the film was once dissolved in the initial stage; however, it was self‐healed via reoxidation of the liberated Mn²⁺ ions. Amperometric flow‐injection analysis of H₂O₂ was carried out with the δ‐MnO₂ film.     

Determination of Uric Acid in the Presence of Ascorbic Acid Using Poly(3,4‐ethylenedioxythiophene)‐Modified Electrodes

A poly(3,4‐ethylenedioxythiophene) (PEDOT) modified glassy carbon electrode (GCE) was used to determine uric acid in the presence of ascorbic acid at physiological pH facilitating a peak potential separation of ascorbic acid and uric acid oxidation (ca. 365 mV), which is the largest value reported so far in the literature. Also, an analytical protocol involving differential pulse voltammetry has been developed using a microchip electrode for the determination of uric acid in the concentration range of 1 to 20 μM in presence of excess of ascorbic acid.     

Enhancement of Antibacterial Capability of Cotton Textiles Coated with TiO2–SiO2/Chitosan Using Hydrophobization

Since textiles have a porous and hydrophilic structure, they are ideal substrates for the settlement and growth of pathogenic bacteria. Therefore, fabrication of hydrophobic textiles to reduce their humidity has the potential to inhibit the growth of bacteria. On this basis, we report here an improvement of the antibacterial capability of textiles coated with TiO₂–SiO₂/chitosan using hydrophobization. Synthesis of TiO₂–SiO₂ clusters with chitosan was carried out using the sol–gel technique. In addition, hydrophobization of the textiles using hexadecyltrimethoxysilane (HDTMS) was carried out using a dip‐spin coating method. In addition, their characteristics were examined using X‐ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectra (UV‐DRS), Fourier transform infrared (FTIR), water contact angle, and antibacterial activity. XRD, SEM, UV‐DRS, FTIR, and water contact angle confirmed the physical and chemical properties of the modified textiles. In summary, the present work shows that the hydrophobization of textiles using HDTMS can enhance the antibacterial capability of cotton textiles.     

Selective Electrochemical Determination of Paracetamol Using Nanostructured Film of Functionalized Thiadiazole Modified Electrode

This paper describes the selective electrochemical determination of paracetamol (PA) in the presence of important interferent, ascorbic acid (AA) using an ultrathin electropolymerized film of 5‐amino‐1,3,4‐thiadiazole‐2‐thiol (p‐ATT) modified glassy carbon (GC) electrode in 0.20 M phosphate buffer solution (pH 7.20). Bare GC electrode failed to resolve the voltammetric signals of AA and PA in a mixture. On the other hand, the p‐ATT modified electrode not only separated the voltammetric signals of AA and PA but also enhanced their peak currents. We achieved the lowest detection limit of 0.34 nM (S/N=3) for PA at p‐ATT modified electrode.