Electrochemical analysis of trifluralin using a nanostructuring electrode with multi-walled carbon nanotubes

The electroanalytical behaviors of the endocrine-disrupting chemical trifluralin have been studied at a nanostructuring electrode. The nanostructuring electrode was fabricated by coating a uniform multi-wall carbon nanotubes/dihexadecyl hydrogen phosphate (MWNTs/DHP) film on glassy carbon electrode (GCE). The reduction peak currents of trifluralin increased remarkably and the reduction peak potential shifted positively at the nanostructuring electrode, compared with that at a bare GCE. The results showed that this nanostructuring electrode exhibited excellent enhancement effects on the electrochemical reduction of trifluralin. Consequently, a simple and sensitive electroanalytical method was developed for the determination of trifluralin. Under optimal conditions, a linear response of trifluralin was obtained in the range from 5.0 × 10⁻⁹ to 6.0 × 10⁻⁶ mol L⁻¹ (r = 0.998) and with a limit of detect (LOD) of 2.0 × 10⁻⁹ mol L⁻¹. The proposed procedure was successfully applied to determine trifluralin in soil samples with satisfactory results.     

Palladium-facilitated electrolytic dechlorination of 2-chlorobiphenyl using a granular-graphite electrode

Palladium-assisted electrocatalytic dechlorination of 2-chlorobiphenyl (2-Cl BP) in aqueous solutions was conducted in a membrane-separated electrochemical reactor with granular-graphite packed electrodes. The dechlorination took place at a granular-graphite cathode while Pd was electro-deposited from the K2PdCl6 in the solution and at a Pd-deposited granular-graphite electrode. Using the Pd-deposited graphite cathode in the membrane reactor for a sequence of experiments, each was conducted under a lower current than in the previous one, and the rate of dechlorination became slower in each consecutive experiment. At the end of this sequence, a duplicate experiment showed a loss of activity of the Pd-deposited granular-graphite cathode. In the experiments of dechlorination while Pd was deposited at the granular-graphite electrode, the rate of dechlorination increased with increases of the initial K2PdCl6 concentration and of the applied cathode potential. In each experiment, the dechlorination of 2-Cl BP was relatively fast at the beginning, as demonstrated in an experiment in which 66.4% of 2-Cl BP was dechlorinated within 4h, but the rate of dechlorination decreased over the time. This decrease can be described with two stages of exponential decrease. The values of the rate constant in the first stage varies with the applied potential and the initial K2PdCl6 concentration, but the values of the rate constant in the second stage do not show any dependence on the potential and the K2PdCl6 concentration. The current efficiency of dechlorination was improved by applying part-time current to the electrodes.     

Electrocatalytic dechlorination of 2,3,5-trichlorophenol on palladium/carbon nanotubes-nafion film/titanium mesh electrode

Environmental Science and Pollution Research - Palladium/carbon nanotubes-nafion film-modified titanium mesh electrode (Pd/CNTs-nafion film/Ti electrode) was prepared and used for catalytic...     

Electrochemical oxidation of bisphenol A. Application to the removal of bisphenol A using a carbon fiber electrode

Leachate samples with a high strength of ammonium-nitrogen (NH4+-N) were collected from a local landfill site in Hong Kong. Two experiments were carried out to study (1) the inhibition of microbial activity of activated sludge by NH4+-N and (2) the chemical precipitation of NH4+-N from leachate as a preliminary treatment prior to the activated sludge process. The experimental results demonstrated that the efficiency of COD removal decreased from 97.7% to 78.1%, and the dehydrogenase activity of activated sludge decreased from 9.29 to 4.93 microg TF/mg MLSS, respectively, when the NH4+-N concentration increased from 53 to 800 mg/l. The experiment also demonstrated that the NH4+-N in the leachate can be quickly precipitated as MgNH4PO4 x 6H2O after addition of MgCl2 x 6H2O + Na2HPO4 x 12H2O. The NH4+-N concentration was reduced from 5618 to 112 mg/l within 15 min when a molar ratio of Mg2+:NH+:PO4(3-) = 1:1:1 was used. The optimum pH to reach the minimum solubility of MgNH4PO4 x 6H2O was found to be in the range of 8.5-9.0. Attention should be given to the high salinity formed in the treated leachate by using MgCl2 x 6H2O + Na2HPO4 x 12H2O, which may affect microbial activity in the following biological treatment processes. Using two other combinations of chemicals [MgO + 85%H3PO4 and Ca(H2PO4)2 x H2O + MgSO4 x 7H2O] could minimise salinity generation after precipitation, while they were less efficient for NH4+-N removal.     

光电催化去除柠檬酸铵中的氨氮

采用阳极氧化法制备了二氧化钛纳米管电极,以制备的二氧化钛纳米管电极为光阳极,采用钛片作为阴极,通过光电催化氧化方法对柠檬酸铵中氨氮进行了去除研究。考察了外加偏压、初始pH值、初始柠檬酸铵浓度,电解质的浓度对氨氮去除的影响。结果表明：与传统的光催化法和电化学法相比,光/电法在柠檬酸铵中氨氮降解过程中存在良好的协同效应;在电压为1.0 V,pH为12,NaCl浓度为0.1 mol·L-1,初始投加柠檬酸铵的量以N计为25 mg·L-1的条件下,紫外光照射下,采用二氧化钛纳米管电极,反应120 min后,柠檬酸铵中氨氮的降解达到60%左右。其中,柠檬酸铵中氨氮的降解产物中N2占82.6%。CaCl2对降解柠檬酸铵起到了加速活化作用。     

Electrochemical analysis of endosulfan using a C18-modified carbon-paste electrode

Successful applications of different analytical procedures to determine quantitatively endosulfan and its metabolites in aqueous media can be found in recent literature. Fundamentally, they have made use of solid-phase extraction (SPE) and gas (GC) or liquid chromatography (LC), sometimes coupled to mass spectrometry (MS). In this paper, a new and alternative methodology to determine quantitatively endosulfan in aqueous media is reported. A C18-modified carbon-paste electrode has been used to determine voltammetrically endosulfan, despite its unfavourable electrochemical properties and behaviour. The methodology proposed is based on the decrease experienced by the peak intensity corresponding to voltammetric signals of Cu(II) when successive and constant additions of endosulfan are carried out. This decrease is directly proportional to the concentration of endosulfan what allows to perform an indirect quantification of the pesticide. The detection limit obtained is 40 ng l⁻¹, this value being under the limits specified by European norms and EPA reports.     

Bimetallic iron-aluminum particles for dechlorination of carbon tetrachloride

Bimetallic iron-aluminum (Fe/Al) particles were synthesized and tested for their reactivity toward carbon tetrachloride using batch reactors and a flow-through column at near neutral pH. Preparation of bimetallic Fe/Al particles was conducted under acidic conditions under which iron was readily deposited onto the aluminum surface. The SEM image showed clusters of iron on the aluminum surface at the measured Fe:Al molar ratio of about 2:3. Results showed that the presence of zero-valent aluminum successfully prevented the formation of a passive layer at the iron surface and maintained the reactivity of iron. The dechlorination of carbon tetrachloride by bimetallic Fe/Al particles produced chloroform (9%), dichloromethane (17%) and methane (38%). Kinetic analysis suggests that bimetallic Fe/Al particles increased the reactivity toward carbon tetrachloride degradation by a factor of 10 compared to zero-valent iron and possessed a comparable reactivity with nano-sized Fe. The effectiveness of bimetallic Fe/Al particles was further confirmed by the continuous flow column study from which an ageing of bimetallic particles was also observed.     

Quantifying chlorinated ethene degradation during reductive dechlorination at Kelly AFB using stable carbon isotopes

Stable isotope analysis of chlorinated ethene contaminants was carried out during a bioaugmentation pilot test at Kelly Air Force Base (AFB) in San Antonio Texas. In this pilot test, cis-1,2-dichloroethene (cDCE) was the primary volatile organic compound. A mixed microbial enrichment culture, KB-1, shown in laboratory experiments to reduce chlorinated ethenes to non-toxic ethene, was added to the pilot test area. Following bioaugmentation with KB-1, perchloroethene (PCE), trichloroethene (TCE) and cDCE concentrations declined, while vinyl chloride (VC) concentrations increased and subsequently decreased as ethene became the dominant transformation product. Shifts in carbon isotopic values up to 2.7 per thousand, 6.4 per thousand, 10.9 per thousand and 10.6 per thousand were observed for PCE, TCE, cDCE and VC, respectively, after bioaugmentation, consistent with the effects of biodegradation. While a rising trend of VC concentrations and the first appearance of ethene were indicative of biodegradation by 72 days post-bioaugmentation, the most compelling evidence of biodegradation was the substantial carbon isotope enrichment (2.0 per thousand to 5.0 per thousand) in ?13C(cDCE). Fractionation factors obtained in previous laboratory studies were used with isotope field measurements to estimate first-order cDCE degradation rate constants of 0.12 h(-1) and 0.17 h(-1) at 115 days post-bioaugmentation. These isotope-derived rate constants were clearly lower than, but within a factor of 2-4 of the previously published rate constant calculated in a parallel study at Kelly AFB using chlorinated ethene concentrations. Stable carbon isotopes can provide not only a sensitive means for early identification of the effects of biodegradation, but an additional means to quantify the rates of biodegradation in the field.     

Photoelectrocatalytic degradation of pentachlorophenol in aqueous solution using a TiO2 nanotube film electrode

Titanium dioxide (TiO2) nanotube film electrodes are fabricated by the anodic oxidation method. Scanning electron microscopy (SEM) showed that these tubes were well aligned and organized into high-density uniform arrays. XRD analysis showed the TiO2 nanotubes to be in the anatase crystal form. The TiO2 nanotube film electrode exhibited increased photoelectrocatalytic (PEC) capability compared to a traditional TiO2 film electrode fabricated using the anodizing method for pentachlorophenol (PCP) degradation in aqueous solution. The bias potential, pH value, and electrolyte concentration were shown to be important factors influencing the degradation of PCP by the PEC method using the TiO2 nanotube film electrode as the working electrode.     

Formation of chloroacetic acids from soil,humic acid and phenolic moieties

The mechanism of formation of chloroacetates, which are important toxic environmental substances, has been controversial. Whereas the anthropogenic production has been well established, a natural formation has also been suggested. In this study the natural formation of chloroacetic acids from soil, as well as from humic material which is present in soil and from phenolic model substances has been investigated. It is shown that chloroacetates are formed from humic material with a linear relationship between the amount of humic acid used and chloroacetates found. More dichloroacetate (DCA) than trichloroacetate (TCA) is produced. The addition of Fe(2+), Fe(3+) and H(2)O(2) leads to an increased yield. NaCl was added as a source of chloride. We further examined the relationship between the structure and reactivity of phenolic substances, which can be considered as monomeric units of humic acids. Ethoxyphenol with built-in ethyl groups forms large amounts of DCA and TCA. The experiments with phenoxyacetic acid yielded large amounts of monochloroacetate (MCA). With other phenolic substances a ring cleavage was observed. Our investigations indicate that chloroacetates are formed abiotically from humic material and soils in addition to their known biotic mode of formation.     

The fate and persistence of trifluoroacetic and chloroacetic acids in pond waters

The environmental fate of trichloro-, dichloro-, and monochloroacetic acids, and trifluoroacetic acid was investigated using field aquatic microcosms and laboratory sediment-water systems. Trifluoroacetic acid was extremely persistent and showed no degradation during a one-year field study, though it appeared to undergo transient partitioning within an unknown pond phase as the temperature of the surroundings was reduced. Of the three chloroacetic acids, trichloro had the longest residence time (induction and decay) (approximately 40 d), dichloro the shortest (approximately 4 d), and monochloro an intermediate residence time (approximately 14 d). Laboratory studies suggest that the biodegradation of trichloro-, dichloro-, and monochloroacetic acids leads primarily to the formation of chloride and oxalic, glyoxalic, and glycolic acids, respectively.     

Electrochemical oxidation of herbicide bifenox acid in aqueous medium using diamond thin film electrode

The electrochemical oxidation of bifenox acid was studied at a boron-doped diamond thin film by cyclic voltammetry and galvanostatic electrolysis. The course of the electrolysis was monitored by measurement of chemical oxygen demand (COD) and by gas chromatography/mass spectrometry (GC / MS) analysis. It was found that exhaustive electrolysis leads to degradation and, ultimately, to mineralization of the starting herbicide. The degradation intermediates were identified showing that the oxidation process begins with the fragmentation of the molecule followed by reactions involving the hydroxyl radical, which is generated by the discharge of water. The study of the effect of current density and concentration showed that the degradation efficiency increases with decreasing current densities and increasing concentrations. The whole results were interpreted in a mechanistic scheme involving two oxidation pathways, the first is a direct oxidation at the electrode and the second uses hydroxyl radical as mediator of the oxidation. Finally, a kinetic study based on spectrophotometric measurements showed that the degradation process is pseudo first order.     

纳米级铁粉脱氯降解四氯化碳

四氯化碳的生产和使用,给人类带来了较大危害.为此,采用纳米铁粉这一新方法对其进行脱氯处理.试验以纳米级铁粉对四氯化碳的脱氯率为考察指标,选用L25(56)正交试验方案,考察了降解介质的初始pH值、纳米铁粉的质量、降解温度、摇床转速和脱氯时间5个影响因素.结果表明,pH值这一因素有极显著影响;在得出的纳米铁粉对四氯化碳脱氯的最佳工艺条件下,获得了99.5%的脱氯率,为有机氯化物脱氯开辟了一条新途径.     

纳米级铁粉脱氯降解四氯化碳

四氯化碳的生产和使用，给人类带来了较大危害。为此，采用纳米铁粉这一新方法对其进行脱氯处理。试验以纳米级铁粉对四氯化碳的脱氯率为考察指标，选用L25（5^6）正交试验方案，考察了降解介质的初始pH值、纳米铁粉的质量、降解温度、摇床转速和脱氯时间5个影响因素。结果表明，pH值这一因素有极显著影响；在得出的纳米铁粉对四氯化碳脱氯的最佳工艺条件下，获得了99．5％的脱氯率，为有机氯化物脱氯开辟了一条新途径。     

Photocatalytic hydrogen generation in the presence of chloroacetic acids over Pt/TiO2

In the presence of chloroacetic acids, the photocatalytic hydrogen evolution and decomposition of the pollutants over Pt/TiO2 have been investigated. The Pt/TiO2 was prepared by photodeposition. Monochloroacetic acid and dichloroacetic acid enhance photocatalytic hydrogen generation, whereas trichloroacetic acid does not. The photocatalytic oxidation of monochloroacetic acid and dichloroacetic acid mainly produces CO2, HCl and formaldehyde, whereas the photocatalytic oxidation of trichloroacetic acid mainly produces CO2 and HCl. The effect of the concentration of monochloroacetic acid and dichloroacetic acid on the hydrogen generation rate is consistent with a Langmuir-Hinshelwood kinetic model. A possible reaction mechanism was discussed.     

Electrochemical treatment of semi-aerobic landfill leachate using Response Surface Methodology (RSM)

This research investigated the effectiveness of electrochemical treatment in treating semi-aerobic landfill leachate. The electrolytic reactor assembly included a pair of aluminium electrodes, a power supply and NaCl as electrolyte. The interactive effects of initial COD, current density and reaction time on treated leachate quality were studied. Regression equations were developed using design-expert software and results were analysed using response surface methodology. At optimum conditions (2000 mg/L initial COD, about 17 mA/cm² current density, 4 h reaction time and 1 g/l NaCl), SCOD removal, BOD removal and colour removal were estimated to be 82.2, 81.5 and 95%, respectively.     

Natural formation and degradation of chloroacetic acids and volatile organochlorines in forest soil--challenges to understanding

- DOI: http:/dx.doi.org/10.1065/espr2005.06.262 Goal, Scope and Background The anthropogenic environmental emissions of chloroacetic acids and volatile organochlorines have been under scrutiny in recent years because the two compound groups are suspected to contribute to forest dieback and stratospheric ozone destruction, respectively. The two organochlorine groups are linked because the atmospheric photochemical oxidation of some volatile organochlorine compounds is one source of phytotoxic chloroacetic acids in the environment. Moreover, both groups are produced in higher amounts by natural chlorination of organic matter, e.g. by soil microorganisms, marine macroalgae and salt lake bacteria, and show similar metabolism pathways. Elucidating the origin and fate of these organohalogens is necessary to implement actions to counteract environmental problems caused by these compounds. Main Features While the anthropogenic sources of chloroacetic acids and volatile organochlorines are relatively well-known and within human control, knowledge of relevant natural processes is scarce and fragmented. This article reviews current knowledge on natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soils, with particular emphasis on processes in the rhizosphere, and discusses future studies necessary to understand the role of forest soils in the formation and degradation of these compounds. Results and Discussion Reviewing the present knowledge of the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil has revealed gaps in knowledge regarding the actual mechanisms behind these processes. In particular, there remains insufficient quantification of reliable budgets and rates of formation and degradation of chloroacetic acids and volatile organochlorines in forest soil (both biotic and abiotic processes) to evaluate the strength of forest ecosystems regarding the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. Conclusion It is concluded that the overall role of forest soil as a source and/or sink for chloroacetic acids and volatile organochlorines is still unclear; the available laboratory and field data reveal only bits of the puzzle. Detailed knowledge of the natural degradation and formation processes in forest soil is important to evaluate the strength of forest ecosystems for the emission and uptake of chloroacetic acids and volatile organochlorines, both on a regional scale and on a global scale. Recommendation and Perspective As the natural formation and degradation processes of chloroacetic acids and volatile organochlorines in forest soil can be influenced by human activities, evaluation of the extent of this influence will help to identify what future actions are needed to reduce human influences and thus prevent further damage to the environment and to human health caused by these compounds.     

Electrochemical treatment of domestic wastewater using boron-doped diamond and nanostructured amorphous carbon electrodes

The performance of the electrochemical oxidation process for efficient treatment of domestic wastewater loaded with organic matter was studied. The process was firstly evaluated in terms of its capability of producing an oxidant agent (H₂O₂) using amorphous carbon (or carbon felt) as cathode, whereas Ti/BDD electrode was used as anode. Relatively high concentrations of H₂O₂ (0.064 mM) was produced after 90 min of electrolysis time, at 4.0 A of current intensity and using amorphous carbon at the cathode. Factorial design and central composite design methodologies were successively used to define the optimal operating conditions to reach maximum removal of chemical oxygen demand (COD) and color. Current intensity and electrolysis time were found to influence the removal of COD and color. The contribution of current intensity on the removal of COD and color was around 59.1 and 58.8 %, respectively, whereas the contribution of treatment time on the removal of COD and color was around 23.2 and 22.9 %, respectively. The electrochemical treatment applied under 3.0 A of current intensity, during 120 min of electrolysis time and using Ti/BDD as anode, was found to be the optimal operating condition in terms of cost/effectiveness. Under these optimal conditions, the average removal rates of COD and color were 78.9?±?2 and 85.5?±?2 %, whereas 70 % of total organic carbon removal was achieved.     

运用BDD电极优化废水中氨氮的直接电化学检测方法

针对高氨氮条件下离子选择电极稳定性差的问题,筛选了3种市售硼掺杂金刚石(BDD)电极,以探究直接电化学检测氨氮的可行性.采用极化曲线法测试了3种BDD电极的析氧、析氢和析氯电位,以获得最佳电势窗口.采用循环伏安法研究了氨氮在3种BDD电极上的氧化还原行为,在1.6 V处发现了明显的氨氮氧化峰,可为氨氮直接检测提供定性依...     

Influences of pH and current on electrolytic dechlorination of trichloroethylene at a granular-graphite packed electrode

Electrolytic dechlorination using a granular-graphite packed cathode is an alternative method for the remediation of chlorinated organic compounds. Its effectiveness under various conditions needs experimental investigation. Dechlorination of trichloroethylene (TCE) was conducted under various conditions in an electrolytic reactor with a platinum-gauze anode and a granular-graphite packed cathode. The higher the applied current, the more TCE was eliminated and more hydrogen and oxygen gasses were generated. Current efficiency decreased with a decrease in TCE concentration during each dechlorination experiment. But, the current efficiency concentration coefficient (CECC), which was defined as current efficiency divided by concentration, was a better indicator of current efficiency. The CECC was not significantly affected by current, but it varied with pH value. The pH effects were results of the involvement of electrolytes in the proton reduction and the electron transfer at the cathode. A lower pH value favored TCE dechlorination in potassium chloride, which is an electrolyte that was not involved in cathode reactions with protons and electrons. In ammonium acetate and potassium nitrate, which involve proton reduction and/or electron transfer, the pH value affected TCE dechlorination through proton limitation and electron competition.