A new strategy for determination of hydroxylamine and phenol in water and waste water samples using modified nanosensor

A carbon paste electrode modified with p-chloranil and carbon nanotubes was used for the sensitive and selective voltammetric determination of hydroxylamine (HX) and phenol (PL). The oxidation of HX at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperommetry, and electrochemical impedance spectroscopy. The values of the catalytic rate constant (k), and diffusion coefficient (D) for HX were calculated. Square wave voltammetric peaks current of HX and PL increased linearly with their concentrations at the ranges of 0.1–172.0 and 5.0–512.0 μmol L^?1, respectively. The detection limits for HX and PL were 0.08 and 2.0 μmol L^?1, respectively. The separation of the anodic peak potentials of HX and PL reached to 0.65 V, using square wave voltammetry. The proposed sensor was successfully applied for the determination of HX and PL in water and wastewater samples.     

An electrochemical nanocomposite modified carbon paste electrode as a sensor for simultaneous determination of hydrazine and phenol in water and wastewater samples

In this study, we report preparation of a high sensitive electrochemical sensor for determination of hydrazine in the presence of phenol in water and wastewater samples. In the first step, we describe synthesis and characterization of ZnO/CNTs nanocomposite with different methods such as transmission electron microscopy (TEM) and X-ray diffraction (XRD). In the second step, application of the synthesis nanocomposite describes the preparation of carbon paste electrode modified with n-(4-hydroxyphenyl)-3,5-dinitrobenzamide as a high sensitive and selective voltammetric sensor for determination of hydrazine and phenol in water and wastewater samples. The mediated oxidation of hydrazine at the modified electrode was investigated by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). Also, the values of catalytic rate constant (k) and diffusion coefficient (D) for hydrazine were calculated. Square wave voltammetry (SWV) of hydrazine at the modified electrode exhibited two linear dynamic ranges with a detection limit (3σ) of 8.0 nmol L^?1. SWV was used for simultaneous determination of hydrazine and phenol at the modified electrode and quantitation of hydrazine and phenol in some real samples by the standard addition method.     

Nylon 6,6 modified screen printed carbon electrodes as electrochemical sensors for rapid chlorothalonil determination in water samples using differential pulse cathodic stripping voltammetry

A newly developed electrochemical sensor for chlorothalonil based on nylon 6,6 film deposited onto screen printed electrode (SPE) with electrochemical modulation of pH at the electrode/solution interface was studied for the first time. Differential pulse cathodic stripping voltammetry (DPCSV) was used to carry out the electrochemical and analytical studies. Experimental parameters such as accumulation potential, initial potential, accumulation time and pH of Britton-Robinson buffer have been optimized. Chlorothalonil gave optimum analytical signal in a medium of 0.04?M Britton-Robinson buffer at pH 6.0. A well-defined reduction peak was observed, at E_p= ?0.851 and ?0.938?V vs. Ag/AgCl (3.0?M KCl) for both bare SPE and modified SPE, respectively. The peak currents of modified SPE were significantly increased as compared to bare SPE. At the modified SPE, a linear relationship between the peak current and chlorothalonil concentration was obtained in the range from 0.1 to 2.8?×?10^?6?M with a detection limit of 1.53?×?10^?8?M (S/N=?3). The practical applicability of the newly developed method has been demonstrated on analyses of real water samples. The newly developed sensor shows good reproducibility with RSD of 3.92%. The nylon 6,6 modified SPE showed itself as promising sensor with good selectivity for chlorothalonil determination.     

Electrochemical study of the fungicide acibenzolar-s-methyl and its voltammetric determination in environmental samples

The electrochemical behavior of new generation fungicide acibenzolar-s-methyl (S-methyl 1,2,3-benzothiadiazole-7-carbothioate, ASM) on the hanging mercury drop electrode (HMDE) was investigated using square wave adsorptive stripping voltammetry. This method of determination is based on the irreversible reduction of ASM at the HMDE. The well-defined ASM peak was observed at ?0.4 V (vs. Ag/AgCl) in BR buffer at pH 2.2. The reduction peak current was proportional to concentration of ASM from 1.0 × 10^?8 to 6.0 × 10^?8 mol L^?1 with detection and quantification limit 3.0 × 10^?9 and 1.0 × 10^?8 mol L^?1, respectively. The applicability of the developed method for analysis of spiked samples of tap water, river water, and soil is illustrated. The effect of adsorption on the mercury electrode was studied in detail using the AC impedance method. Possible interferences with other common pesticides and heavy metal ions were examined. Clarification of the electrode mechanism was made using cyclic voltammetry (CV) technique.     

Electrochemical oxidation of sulfite ions in aqueous solutions

Gaseous pollutants that affect human health, destroy vegetation and damage materials and art treasures can be converted into harmless components by electrochemical reactions. Electrochemical gas purification methods can be applied basically in two steps. In the first step, gases to be removed are absorbed in an aqueous electrolyte. Then, in the second step, they can be converted into harmless components via electrochemical oxidation or electrochemical reduction. This study investigated the feasibility of electrochemical removal of sulfite ions arising from the absorption of sulfur dioxide in an aqueous electrolyte. The removal efficiency, current efficiency, and energy consumption were determined at different initial sulfite ion and electrolyte concentrations and applied currents. Furthermore, linear sweep voltammetry studies were performed using a graphite electrode in sulfuric acid. It has been concluded from all these experiments that sulfur dioxide can successfully be removed using an electrochemical method.     

Nanocellulosic fiber-modified carbon paste electrode for ultra trace determination of Cd (II) and Pb (II) in aqueous solution

In recent years, increasing awareness of the environmental impact of heavy metals has prompted a demand for monitoring and decontaminating industrial wastes prior to discharging into natural water bodies. This paper describes the preparation and electrochemical application of carbon paste electrode modified with nanocellulosic fibers for the determination of cadmium and lead in water samples using anodic stripping voltammetry. First, cadmium and lead were adsorbed on the carbon paste electrode surface at open circuit potential, followed by anodic stripping voltammetric scan from -1 to 0 V. Different factors affecting sensitivity and precision of the electrode, including accumulating solvent, pH of the accumulating solvent, accumulation time, supporting electrolyte, and scan rate were investigated. The proposed method was also applied to the determination of Cd (II) and Pb (II) in the presence of other interfering metal ions and cetyl trimethyl ammonium bromide, sodium dodecyl sulfate, and Triton X-100 as a representative of cationic, anionic, and neutral surfactants. Linear calibration curves were obtained in the concentration ranges of 150–650 μg?L^?1 and 80–300 μg?L^?1, respectively, for cadmium and lead at an accumulated time of 10 min with limits of detection 88 and 33 μg?L^?1. Optimized working conditions are defined as acetate buffer of pH?5 as accumulating solvent, hydrochloric acid as supporting electrolyte, and scan rate 50 mV/s. This technique does not use mercury and therefore has a positive environmental benefit. The method is reasonably sensitive and selective and has been successfully applied to the determination of trace amounts of Cd (II) and Pb (II) in water samples.     

Electroassisted methods for waste destruction: silver(II) and peroxydisulfate reagents in the electrochemically mediated oxidation of polyaromatic sulfonates

The electrochemical oxidation is a promising process for organic pollutants which are recalcitrant to biological degradation. The anodic oxidation of 1,5-naphthalenedisulfonic acid, hereafter NDS, was evaluated at a Pt anode using in situ generated Ag(II) cation or peroxydisulfate [S2O(8)(2-)] anion as mediators. Kinetics of the direct chemical oxidation of NDS in the presence of Na2S2O8, and the identification of some oxidation intermediates are also reported. An analysis of the results shows that Ag(II) is characterized by a high-reaction rates, while [S2O(8)(2-)] performs the oxidation of NDS in a complete way.     

Direct electrochemical detection of glyphosate at carbon paste electrode and its determination in samples of milk,orange juice,and agricultural formulation

Abstract

This paper describes a simple, inexpensive, highly sensitive, selective, and efficient electrochemical method to determine glyphosate (GLY) in samples of milk, orange juice, and agricultural formulation. The oxidation reaction on the electrode surface was electrochemically characterised by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of GLY at carbon paste electrode revealed a non-reversible oxidation peak at +0.95 V versus Ag/AgCl, which was used for electrochemical detection of GLY. The operating parameters (pH, frequency, step potential, and amplitude) were optimised in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 4.40?×?10^?8–2.80?×?10^?6 mol L^?1, with a detection limit of 2?×?10^?9 mol L^?1. After calibration curve was plotted, the developed procedure was applied to determine GLY in previously contaminated samples: milk and orange juice, and in a commercial formulation, obtaining recovery values between 98.31% and 103.75%. These results show that the proposed method can be used for GLY quantification in different samples with high sensitivity, specificity, stability, and reproducibility.     

Evaluation of different electrochemical methods on the oxidation and degradation of Reactive Blue 4 in aqueous solution

The oxidation of a reactive dye, Reactive Blue 4, RB4, (C.I. 61205), widely used in the textile industries to color natural fibers, was studied by electrochemical techniques. The oxidation on glassy carbon electrode and reticulated vitreous carbon electrode occurs in only one step at 2.0 < pH < 12 involving a two-electron transfer to the amine group leading to the imide derivative. Dye solution was not decolorized effectively in this electrolysis process. Nevertheless, the oxidation of this dye on Ti/SnO2/SbO(x) (3% mol)/RuO2 (1% mol) electrode showed 100% of decolorization and 60% of total organic carbon removal in Na2SO4 0.2 M at pH 2.2 and potential of +2.4V. Experiments on degradation photoelectrocatalytic were also carried out for RB4 degradation in Na2SO4 0.1 M, pH 12, using a Ti/TiO2 photoanode biased at +1.0 V and UV light. After 1h of electrolysis the results indicated total color removal and 37% of mineralization.     

Effects of surface coatings on electrochemical properties and contaminant sorption of clay minerals

Surface charges play a major role in determining the interactions of contaminants with soils. The most important sources of soil charges are clay mineral colloids, whose electrochemical properties are usually modified by metal-oxides and organic matter in natural environments. In this study, effects of coatings of organic matter and Fe- and Al-oxides on a series of electrochemical properties and heavy metal sorption of three clay minerals (kaolinite, montmorillonite and illite) predominant in natural soils were investigated using batch techniques. The results indicate that the coatings increased the specific surface area of the clay minerals, except for the Al-oxide coated montmorillonite and organic matter coated 2:1 clay minerals. The sesquioxide coatings increased amount of positive charges but decreased negative charges. This causes great reduction of the negative potential on the clay surfaces, shift of the zero point of charge to a higher pH, and promotion of fluoride sorption due to presence of more OH- and OH2 on the oxide surfaces than on the clay surfaces. In contrast, the organic coating significantly increased the negativity of surface charges, and thus the zero point of charge and zeta-potential of the clays dropped down. The organic coating also induced a reduction of fluoride sorption on the clays. With respect to the sorption of lead and cadmium, the sesquioxide coatings produced insignificant effects. The experiments of lead/cadmium competitive sorption show that on both the oxide-coated surface and the original clay surface there exist different types of sites, each of which preferentially binds with a heavy metal.     

Evaluation of the electrochemical behavior of pentachlorophenol by cyclic voltammetry on carbon paste electrode modified by humic acids.

Humic substances, or natural recalcitrant organic matter, have an important role in the environment for their plant nutritional functions or for their capability to control the mobility of xenobiotic substances, such as pesticides. To verify the electrochemical behavior of pentachlorophenol (PCP), cyclic voltammetry was used because of its versatility. The following two different electrodes were used: carbon paste electrode (CPE) and carbon paste electrode chemically modified with humic acid (HACMCPE). The results demonstrated that PCP was better accumulated at the HACMCPE electrode, as a consequence of a larger current signal than at the CPE electrode. Cyclic voltammograms showed oxidation steps of PCP itself and probable production of quinonelike compounds.     

Simultaneous decontamination of hexavalent chromium and methyl tert-butyl ether by UV/TiO2 process

Hexavalent chromium and methyl tert-butyl ether (MTBE) are two important environmental pollutants. Simultaneous decontamination of Cr(VI) and MTBE was studied by UV/TiO2 process. The influences of pH and the concentrations of pollutants on the kinetics of the photocatalytic reactions were evaluated. Dark adsorption tests showed that the acidic pH favored the adsorption of Cr(VI) while neutral pH favored the adsorption of MTBE. Under UV irradiation, Cr(VI) reduction was observed in Cr(VI)/TiO2 system, and MTBE oxidation was observed in MTBE/TiO2 system. The system containing Cr(VI) and MTBE by UV/TiO2 process demonstrated the synergistic effect between oxidation of MTBE and reduction of Cr(VI). The results demonstrated that two pollutants Cr(VI) and MTBE could be eliminated simultaneously by UV/TiO2 process. tert-Butyl formate, tert-butyl alcohol and acetone were identified as primary degradation products of MTBE by gas chromatography-mass spectrometry in the degradation of MTBE by UV/TiO2 process.     

Study on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos

In this paper, dichromate and dichlorvos are selected as the deputies of inorganic and organic pollutants, respectively, and TiO2/beads is used as a photocatalyst. The effects of various parameters, such as the amount of the photocatalyst, H2O2 concentration, metal ions, anions, pH value, and organic compounds on the photocatalytic reduction of dichromate and photocatalytic oxidation of dichlorvos are studied. From the studies, the differences of the parameters effect on the photocatalytic degradation of organic and inorganic pollutants are obtained. The results show that the optimum amount of the photocatalyst used is 6.0 g cm(-3) for the photocatalytic reactions. With the addition of a small amount of H2O2, the photocatalytic reduction of dichromate is inhibited while the photocatalytic oxidation of dichlorvos is accelerated. With the addition of trace amounts of Fe3+ or Cu2+, both the reactions are accelerated, and with the addition of Zn2+ and Na+, no obvious effects on the reactions are observed. Acidic solution is favorable for the photocatalytic reduction of dichromate; and acidic and alkaline solutions are favorable for the photocatalytic oxidation of dichlorvos. Adding SO4(2-), the photocatalytic oxidation is accelerated and adding Cl- the reaction is inhibited; and with the addition of trace amounts of SO4(2-), Cl- and NO3-, no obvious effects on the photocatalytic reduction of dichromate are observed. With the addition of methanol and toluene, the photocatalytic reduction of dichromate is accelerated, and the photocatalytic oxidation of dichlorvos is inhibited. The possible roles of the additives on the reactions are also discussed.     

电催化氧化技术处理制革综合废水

选择DSA电极中的钛基掺硼金钢石膜电极(Ti/BDD),用于制革综合废水的电催化氧化处理研究,考察了在不同的电流密度、电压、电解质、pH值和电解时间等因素对COD去除率和电流效率的影响。结果表明,控制电流密度为30mA/cm2,电压为8.0 V,电解质(NaCl)浓度为2.0 g/L,pH为4.0,电催化氧化处理2 h后,废水的COD和NH4+-N的去除率分别达到了83.6%和90.3%,BOD/COD为0.45,比能耗为35.34 kWh/kg COD,电流效率为37%。     

Assessment of the functionality of a pilot-scale reactor and its potential for electrochemical degradation of calmagite, a sulfonated azo-dye

Electrochemical degradation (ECD) is a promising technology for in situ remediation of diversely contaminated environmental matrices by application of a low level electric potential gradient. This investigation, prompted by successful bench-scale ECD of trichloroethylene, involved development, parametric characterization and evaluation of a pilot-scale electrochemical reactor for degradation of calmagite, a sulfonated azo-dye used as a model contaminant. The reactor has two chambers filled with granulated graphite for electrodes. The system has electrical potential, current, conductivity, pH, temperature, water-level and flow sensors for automated monitoring. The reactor supports outdoor and fail-safe venting, argon purging, temperature regulation and auto-shutdown for safety. Treatment involves recirculating the contaminated solution through the electrode beds at small flow velocities mimicking low fluid-flux in groundwater and submarine sediments. The first phase of the investigation involved testing of the reactor components, its parametric probes and the automated data acquisition system for performance as designed. The results showed hydraulic stability, consistent pH behavior, marginal temperature rise (<5 degrees C) and overall safe and predictable performance under diverse conditions. Near complete removal of calmagite was seen at 3-10V of applied voltage in 8-10h. The effects of voltage and strength of electrolyte on degradation kinetics have been presented. Further, it was observed from the absorption spectra that as calmagite degrades over time, new peaks appear. These peaks were associated with degradation products identified using electrospray ionization mass spectrometry. A reaction mechanism for ECD of calmagite has also been proposed.     

电化学催化降解水中有机污染物的研究进展

电化学法催化降解废水中的有机污染物已引起广泛兴趣。在电极的作用下 ,电化学反应和化学催化作用结合 ,可导致有机分子的电催化降解。选用合适的电极材料可以加速电化学反应速率 ,有助于有机物的电化学转化。本文讨论了提高电催化降解速率的方法 ,指出了在该领域的研究中存在的问题和发展方向     

Voltammetric detection of trifluralin in tap water,fruit juice,and vegetable extracts in the presence of surfactants

This study describes a novel electrochemical method to determine the herbicide trifluralin in samples of water, fruit juice, and vegetable extracts in the presence of surfactants, using a glassy carbon electrode (GCE). In acidic media, trifluralin was irreversible on the glassy carbon electrode surface at ?0.5 V vs. Ag/AgCl. Surfactant presence on the electrode–solution interface modified current intensities and shifted the reduction peak potential of trifluralin. Different types of surfactant and their concentrations were investigated. The anionic surfactant significantly enhanced the peak current intensity of trifluralin. Under optimal analytical conditions, an analytical curve was obtained in the concentration range of 0.48–32.20 µM. The limits of detection and quantification were estimated at 0.031 and 0.104 µM, respectively. The method was successfully applied to quantify trifluralin in samples of water, orange and tomato juice, and green pepper, carrot, and onion extracts, with recovery rates of 97.9–102.1%. The results were in good agreement with those obtained using high-performance liquid chromatography, indicating that the proposed electrochemical method can be employed to quantify trifluralin in various types foods, with sensitivity, specificity, selectivity and reproducibility.     

组合阳极联合气体扩散阴极电催化降解苯胺

采用气体扩散电极为阴极,钛基氧化物（Ti／SnO2-Sb2O5-IrO2）和金属铁构成组合阳极,构建了新型电化学氧化体系用于降解有机污染物。利用该氧化体系,在不同实验条件下考察了苯胺降解的效果与降解过程的相关规律。结果表明,阴极电位、铁阳极通电时间以及苯胺初始浓度均显著影响苯胺的降解效果。当阴极电位为-0．7V,pH3．0,铁阳极通电时间20min时,电化学处理200mg／L苯胺480min,TOC的去除效率达到80．4％,矿化电流效率（MCE）为8．6％,显示了该氧化体系具有良好的有机物降解能力。此外,苯胺降解过程中氨氮和硝态氮浓度的变化表明,苯胺分子中的氮主要转化为NH4和NO3^-。     

响应曲面法优化电化学氧化技术处理染料废水

采用IR和XRD等手段对自制磷钼酸铁(FePMo12)杂多酸进行表征,表明杂多阴离子具有Keggin结构。将FePMo12负载于修饰后的分子筛上制备FePMo12/APTES-4A催化剂填充于电化学反应器中,考察电化学氧化体系对酸性大红3R染料废水的脱色效果,其脱色率高于二维电化学反应器。利用Box-Behnken中心组合实验设计及响应面(RSM)分析,以pH值,板间距,槽电压,曝气量为实验因素,建立了以酸性大红3R的脱色率为响应值的二次多项式回归模型。研究表明,当电解时间为60 min时,曝气量0.05 m3/h、pH为2、板间距3.0 cm、槽电压11.0 V,在此条件下色度去除率可达69.4%,模型预测值与实验值能很好地吻合。方差分析结果表明,槽电压和pH、pH和曝气量的交互作用对响应值具有显著性影响。     

Identification of a novel fluorescent adduct formed in the reaction of malonaldehyde with adenosine

Malonaldehyde was reacted with adenosine in aqueous solution at acidic conditions and the reaction mixtures were analysed by HPLC. Four major product peaks were observed in the chromatogram recorded by the UV detector at 320 nm. Two of the peaks could be deduced to the previously characterised malonaldehyde-adenosine reaction product 9-(beta-D-ribofuranosyl)-6-(5,7-diformyl-2H-3,6-dihydro-2,6-methano-1,3-oxazocin-3-yl)purine (M3A) and to the ribose analogue of the 2'-deoxy adduct 9-(2'-deoxy-beta-D-ribofuranosyl)-6-(3,5-diformyl-4-methyl-1,4-dihydro-1-pyridyl)purine (M2AA-dA). The two other peaks were due to previously uncharacterised adducts. Upon isolation of these adduct peaks it was found that the peaks are interconverted to each other, one adduct peak dominating over the other one. On the basis of data recorded by UV, fluorescence and 1H NMR spectroscopy, and mass spectrometry, the structure of the major adduct could be determined as 9-(beta-D-ribofuranosyl)-6-(3,5-diformyl-4-etanal-1,4-dihydro-1-pyridyl)purine (3M-A). The adduct is most likely formed by reaction of adenosine with a malonaldehyde condensation product consisting of three units of malonaldehyde. The highest yield of 3M-A was obtained in the reaction performed at pH 4.6 and 80 degrees C for 75 h. The minor form of the interconverting peaks could not be characterised on the basis of the spectral data. However, it is concluded that the minor peak most likely represents the hydrated form of 3M-A. Since these adducts are formed only in trace amounts at neutral pH and 37 degrees C and the formation requires high amounts of malonaldehyde, it is likely that the adducts are not formed in DNA in vivo and thus not contribute to the malonaldehyde genotoxicity.