Ammonia oxidation to nitrogen mediated by electrogenerated active chlorine on Ti/PtOx-IrO2

The electrochemical oxidation of ammonia (NH₃ and/or NH₄⁺) in the presence of chloride was investigated on a Ti/PtO_x–IrO₂ electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N₂ and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.     

Catalytic generation of chlorine with slight overpotential by micellar ferrocene

Ferrocene solubilized with poly(vinylpyrrolidone) in aqueous KCl solution exhibited a well-defined voltammetric peak at 1.33 V vs. Ag∣AgCl at a platinum electrode. The wave was attributed to the oxidation of chloride to chlorine, demonstrated by smell of chlorine, by a view of formation of gas bubbles, by coloration through the reaction with diethyl-p-phenylene diamine, and by the increase in the anodic current with the concentration of chloride. Since no wave was observed in the ferrocene-free solution or KCl-free solution in this potential domain, the reaction mechanism was suggested to be the oxidation of chloride into chlorine catalyzed by micellar ferrocene. The potential at the foot of the wave (1.08 V) was less positive that the standard potential of Cl₂/Cl⁻, and hence the reaction may be useful for enhancing the energetic efficiency at chlor-alkali industry. The value of the peak current was one-sixth the theoretical diffusion-controlled current, and was proportional to the square-root of the potential scan rate.     

Investigation of interference mechanisms of nickel chloride on copper determination and of colloidal palladium as modifier in electrothermal atomic absorption spectrometry using a dual cavity platform

The interference of nickel chloride on the determination of copper by electrothermal atomic absorption spectrometry was investigated using a specially designed dual cavity platform (DCP), which allows the analyte and interferent to vaporize from separate cavities, so that gas and condensed phase interferences can be distinguished to some extent. It was found that, when low pyrolysis temperatures were used, the interference of nickel chloride on copper originated from the formation of copper chloride in the condensed phase, which is not efficiently dissociated in the atomization stage. Alternately, when analyte and interferent were in separate cavities of the DCP, a gas-phase reaction between copper and chlorine in the atomization stage resulted in a similar signal depression. When higher pyrolysis temperatures were used, interference could be attributed to losses of volatile copper chloride in the pyrolysis stage. These losses were more pronounced when analyte and interferent were in separate cavities of the DCP, indicating again a gas-phase reaction between copper and chlorine, as well as a protective action of nickel oxide, when analyte and interferent were mixed. Colloidal palladium used as modifier removed the chloride interference independent of the pyrolysis temperature applied, when copper and nickel chloride were mixed. Colloidal palladium also increased the integrated absorbance for copper by 40–50%, even when analyte and modifier were in separate cavities of the DCP, indicating a strong gas-phase interaction between copper atoms and the modifier through adsorption/desorption processes.     

Donor-Acceptor Complexes in Copolymerization. LIX. Alternating Diene-Dienophile Copolymers. 13. Copolymerization of Dicyclopentadiene and Maleic Anhydride

The solution and bulk copolymerization of dicyclopentadiene (DCP) and maleic anhydride (MAH) occurs over the temperature range 80–240°C, upon the addition of a free-radical catalyst which has a short half-life at the reaction temperature. An unsaturated 1/1 MAH/DCP copolymer, derived from the copolymerization of MAH with the norbornene double bond, followed by a Wagner-Meerwein rearrangement, is obtained in the presence of a large excess of DCP at 80° C, while a saturated 2/1 MAH/ DCP copolymer, derived from the cyclocopolymerization of the residual cyclopentene unsaturation, is obtained at higher temperatures or in the presence of excess MAH. The copolymers prepared under other conditions with intermediate MAH/DCP mole ratios contain both 1/1 and 2/1 repeating units. The copolymer obtained from bulk copolymerization above 170° C contains units derived from cyclopentadiene-MAH cyclocopolymerization as well as DCP-MAH copolymerization.     

Phenol Conversions during Electrochemical Generation of Active Chlorine

Data on the electrochemical oxidation of a model phenol solution (100 mg/l) in the presence of sodium chloride (10 g/l) are presented. It is shown that active chlorine yielded by the electrolysis is directly involved in the electrochemical oxidation of phenol, which proceeds with destruction of the aromatic ring. In the course of the oxidation of the model phenol solution on Pt/Pt, under the conditions of electrochemical generation of active chlorine, no dioxine structures form.     

Adsorption of octadecyltrimethylammonium chloride and adsolubilization on to cellulosic fibers

The coadsorption of different organic solutes on cellulosic fibers treated with octadecyltrimethylammonium chloride (ODTMA) has been studied. In the absence of ODTMA cellulosic fibers had little tendency to retain organic compounds. The enhanced solute incorporation was ascribed to the adsolubilization of these compounds on the aggregated domains of the adsorbed surfactant molecules at the solid/liquid interface. The specific shape of solute coadsorption isotherms indicated that the adsolubilization process may be regarded as a partition phenomenon between the aqueous bulk phase and the adsorbed surfactant aggregates. The decrease in solute uptake at the cellulose/water interface above the CMC of ODTMA was ascribed to micelle formation in the bulk solution and to the ensuing micellar solubilization of organic solutes. Preliminary experiments performed using vertical fixed bed columns showed that modified cellulosic fibers can be conveniently used as substrate for treating organic pollutants.     

OXIDATIVE ADDITION REACTIONS OF d8 COMPLEXES. I. CHLORINE OXIDATION OF TETRACHOLOROPALLADATE (II)

Abstract

The reaction of Na₂PdCl₄ with chlorine in aqueous acid solution proceeds in two stages: oxidation of the complex to a Pd(IV) species followed by a slower substitution reaction. The oxidation reaction is first order in complex and first order in chlorine. At high chloride concentration, a six-coordinate palladium(II) intermediate is formed, which is oxidised via an outer-sphere type mechanism. Oxidation of the chloroaquopalladium(II) species present at low chloride concentration occurs via a different mechanism, probably involving coordination of the oxidant in a ‘quasiinner-sphere’ mechanism.     

Ion chromatography-electrospray mass spectrometry for the identification of low-molecular-weight organic acids during the 2,4-dichlorophenol degradation

End-product identification of organic pollutants during oxidation water treatments is of environmental concern due to their potential toxicity. In this work the coupling of ion chromatography (IC), equipped with a membrane ion suppressor, and electrospray ionization mass spectrometry (ESI-MS) has been successfully exploited for the identification of novel low molecular weight organic acids formed as final by-products of 2,4-dichloro-phenol (DCP) degradation by Fenton's reagent, an oxidation method widely employed to degrade recalcitrant organic pollutants in industrial wastewater. The IC-ESI-MS analytical set-up not only allowed the detection of known organic acids but also the identification of 13 new low molecular weight organic acids as a result of extensive oxidation of the parent organic pollutant. Some of the novel organic acids were shown to be chlorine containing by-products and, consequently, of environmental concern. The analytical set-up could be used for characterizing the unknown organic carbon fraction arising from oxidation water treatments.     

The activity and selectivity of catalytic peroxide oxidation of chlorophenols over Cu-Al hydrotalcite/clay composite

Liquid phase catalytic oxidation of chlorophenols (CPs) was carried out over Cu-Al hydrotalcite/clay composite at ambient temperature and pressure using hydrogen peroxide as oxidant. The results showed that the catalyst had high catalytic activity, with complete oxidation of 4-CP within 40 min at 40 °C. The content and position of chlorine on the aromatic ring had significantly different effects on the oxidation rate of CPs, with the rate sequence of phenol > monochlorophenol (MCP) > dichlorophenol (DCP) > trichlorophenol (TCP), 3-CP > 2-CP > 4-CP, and 3,5-DCP > 3,4-DCP > 2,5-DCP > 2,4-DCP > 2,6-DCP. This was ascribed to the interactions among σ-electron withdrawing conductive effect, π-electron donating conjugative effect, and steric hindrance effect of chlorine. It was evidenced that the catalytic peroxide oxidation of CPs in the first step was selective and rate-limiting, where chlorinated 1,4-benzoquinones formed.     

Behavior of Porous Titanium and Catalytically Active Electrodes Based on It in Acidic Chloride Solutions

The behavior of porous titanium and electrodes based on it, which are activated with Pt, Au, RuO₂, Co₃O₄, and MnO₂, in 20-% LiCl solution (pH –0.4 to –0.5) is studied. On porous titanium in the potential ranges 0.1 < E< 0.5 and 0.5 < E< 1.1 V (NHE), the formation of titanium hydrides and passive oxide layers, respectively, is observed; the processes decay with time. In the ranges E< 0.1 and E> 1.1 V, the dissolved oxygen reduction and chlorine evolution, respectively, are observed on porous titanium at high overpotentials. On porous titanium activated with thin-layer Pt, Au, and RuO₂coatings, the functional Evs. pH dependence, which is typical for these electrocatalysts, breaks down due to the conjugate reactions of titanium oxidation. On porous titanium activated with Co₃O₄and MnO₂, at pH below unity, chlorine evolution is observed; its rate is limited by the chlorine mass transfer into the bulk solution. Under a gas-diffusion control, the chlorine evolution rate is determined by the diffusion of absorbed hydrogen chloride. The conditions of application of porous titanium as the support for catalytically active electrodes of electrochemical sensors in acidic chloride solutions are considered.     

Selective modification of mono-altro-β-cyclodextrin: dependence of O-sulfonylation position on the shape of sulfonylating reactant

Mono-altro-β-cyclodextrin, which has 21 different hydroxyl groups, was selectively sulfonylated by 2-naphthalenesulfonyl chloride at the 2^A-OH of the altrose residue. By using 1-naphthalenesulfonyl chloride as reactant, the 3^G-OH of the neighboring glucose became available for selective sulfonylation, and the resulted sulfonate was proved to be a very important intermediate for introducing functionalities to the saccharide adjacent to the altroside of mono-altro-β-cyclodextrin that is capable of controlling the orientation of substrate.     

Reduction of perchlorate using zero-valent titanium (ZVT) anode: Kinetic models

The kinetics of perchlorate reduction by zero-valent titanium (ZVT) undergoing electrical pitting corrosion was described by interactions of two domains (pit and solution). Two kinetic models were developed based on two possible inhibition mechanisms. A competitive adsorption model was developed based on surface coverage of perchlorate and chloride on bare ZVT, and a Ti(II) consumption model was developed based on Ti(II) oxidation by electrochemically developed chlorine. Both models well predicted perchlorate concentration changes in the solution. The competitive adsorption model showed that chloride has a higher adsorption affinity on both sites where oxidative dissolution of ZVT occurs and where chloride oxidation occurs. Also, the rates of perchlorate removal and chloride oxidation were directly proportional to current applied. For the Ti(II) consumption model, the rate constant of Ti(II) production was dependent on current. The rate of chloride oxidation is also believed to be proportional to current, but this conclusion cannot be made with confidence. Both kinetic models described changes in perchlorate concentration well. However, the Ti(II) consumption model was limited in its ability to predict chloride concentration. This limitation was probably caused by a lack of available information like electrochemical oxidation of chloride on bare ZVT and Ti(II) oxidation by chlorine.     

多次高温裂解、富集-离子色谱法检测己内酰胺中的痕量氯

建立了多次高温裂解、富集-离子色谱检测己内酰胺(CPL)中痕量氯的分析方法。CPL样品在富氧环境下经3次高温(800℃)裂解后,痕量有机氯转化为氯气或氯化氢气体,经5 mL 10 mmol/L的NaOH溶液吸收、富集,然后转化为氯离子,在阴离子抑制电导检测模式下进行离子色谱分析,检测其中氯离子(Cl-)的含量。在优化的条件下,Cl-在0.05~1.0 mg/L范围内呈良好线性,相关系数为0.999 7,方法检出限为0.37μg/g。对0.8 mg/L的Cl-标准溶液连续进样7次,其保留时间、峰面积、峰高的RSD分别为0.04%、0.24%和0.20%;分别对CPL样品进行处理和检测,得到痕量氯含量的RSD为1.52%(n=4);Cl-标准溶液的转化率为93.3%~104.0%,CPL样品的加标回收率为95.3%~113.1%。该方法操作简单、前处理条件可控、重复性好、检出限低,可满足实际样品中痕量氯的检测。     

SXPS analysis of passivation and complexation on the CdS (101¯ 0) surface

CdS(101ˉ 0) surfaces were chemically modified by oxidation in air or UV/ozone, sulfurization after treatment with a Br₂-methanol solution and reaction with the multidendate organic reactant 2-mercaptobenzothiazole (MBT). Surface sensitive photoelectron spectra from tuned excitation using synchrotron radiation (SXPS) show that initial oxidation by air gives monolayer coverages of sulfate (with minor contributions of sulfite) and chemisorbed polysulfur species passivating the surface. In contrast to this behavior the oxidation by UV/ozone proceeds very fast, giving thick sulfate layers. Thick layers of elemental sulfur are created during Br₂-methanol treatment. SXPS results show that a monolayer of chemisorbed polysulfide between the sulfur coverage and the sulfide is only removed by annealing the substrate up to 500 K. The reaction of MBT with the CdS surface is photochemically activated giving a submonolayer of MBT/adsorbate complex covered by bis(2-benzothiazolyl)disulfide (BBTD). A scheme of the photoinduced oxidation mechanism creating the disulfide is proposed. Received: 30 July 1997 / Accepted: 23 January 1998     

Surface reactions of chlorine molecules and atoms with water and sulfuric acid at low temperatures

Reactions of chlorine-containing species are of great current interest, particularly in reference to possible stratospheric ozone depletion. We have been investigating the potential role of heterogeneous reactions of these species with stratospheric aerosols. Here we wish to report on the results of a study of the interactions of Cl atoms and Cl₂ with H₂SO₄ and H₂O, the dominant components of stratospheric aerosols, at low temperature using X-ray photoelectron spectroscopy (XPS). It appears that chlorine atoms and molecules form chloride ion and higher oxidation states of chlorine upon reacting with cooled surfuric acid surfaces while only chloride ion forms with ice. To test the validity of the chlorine oxidation assignment, an XPS study was also made of chlorine in its various oxidation states as found in the chlorides, hypochlorites, chlorites, chlorates, and perchlorates of sodium, potassium, and calcium. Possible mechanisms by which chlorine changes its oxidation state on contact with H₂SO₄ glasses are discussed.     

Modeling of Gaseous Chlorine Production in a Static Electrolyzer

Transfer of hydroxide and hydroxonium ions in bulk of sodium chloride solution in the course of gaseous chlorine production in a static electrolyzer was considered and a relationship was derived to deter- mine the characteristics of a chlorinator. Principles of selecting electrolyzer currents to obtain gaseous chlorine in a static chlorinator were recommended.     

Some observations on an indirect atomic absorption spectrophotometric method for the microdetermination of chlorine or bromine in organic compounds

An atomic absorption spectrophotometric method for the microdetermination of chlorine or bromine in organic compounds is described; it is based on oxygen flask combustion to yield chloride or bromide, which is then reacted with an excess of solid silver chromate, followed by collection of the combined unreacted silver chromate and chloride or bromide preipitate and AAS determination of the free chromate (equivalent of the chloride or bromide originally present) at 358.2 nm. The method was applied satisfactorily to a wide range of chlorine or bromine containing organic compounds with an average absolute error of ± 0.23 and a coefficient of variation (seven determinations) of better than 2%.     

Performance of glucose electrooxidation on Ni–Co composition dispersed on the poly(isonicotinic acid) (SDS) film

Poly(isonicotinic acid) (PINA) film was electrosynthesized on carbon paste electrode (CPE) by using the repeated potential cycling technique in aqueous solution containing isonicotinic acid (INA), sulfuric acid and sodium dodecyl sulfate (SDS). Then, nickel and cobalt ions were incorporated by immersion of CPE/PINA prepared in the presence of SDS (CPE/PINA(SDS)) in a solution with different proportions of nickel chloride and cobalt chloride. The electrochemical characterization of mixed hydroxides containing cobalt and nickel at the surface of the modified electrode is presented. The modified electrodes were successfully used in the electrocatalytic oxidation of glucose. Finally, the electrocatalytic oxidation peak currents of glucose exhibited a good linear dependence on concentration, and its quantification can be done easily. The good analytical performance, low cost and straightforward preparation method make this novel electrode material promising for the development of an effective glucose sensor.     

高浓度含酚废水中酚类的转化回收及脱除

以含量30 g/L的苯酚水溶液为模型,提出氯化联合氧化工艺,实现对高浓度含酚废水中苯酚的转化回收及残余酚类的氧化脱除。 首先以pH值作为指示,向溶液中引入足够量的氯离子和氢离子,通过加入氯酸钠与之反应定量产生氯气;在所控制的实验条件下,氯气与溶液中的苯酚选择性反应转化为低溶解度的三氯苯酚沉淀,经气相色谱-质谱（GC-MS）面积归一法测得其含量可达97.76%;过滤所得滤液化学需氧量（COD）降低至1125 mg/L,苯酚回收率约98.7%。 采用Fenton氧化技术对该滤液进行氧化降解,结果表明,在优化的实验条件pH=3、Fe2+浓度为1 mmol/L下,H2O2用量为15 mL/L时,残余的氯酚类即可以被有效降解,降解后的水样经调碱性将铁或亚铁离子沉淀后为无色透明的溶液;联合处理后,水样COD减小到52 mg/L,该值满足国家工业污水排放标准。     

Hydrogen Peroxide Detection at Electrochemically and Sol‐Gel Derived Ir Oxide Films

Ir oxide (IrOx) films, formed electrochemically on bulk Ir metal (Ir/IrOx) and also on sol‐gel (SG) derived non‐silica based nanoparticulate Ir, have been studied as material useful for the detection of hydrogen peroxide, with possible application as a glucose biosensor. H₂O₂ reduction and oxidation on Ir/IrOx and SG‐derived IrOx films, deposited on various substrates such as Pt, Ir and GC, have been compared to the H₂O₂ behavior at the bare substrate. It was found that H₂O₂ reduction proceeds on the underlying electrode substrate, while H₂O₂ oxidation is independent of the nature of the substrate, therefore occurring via the IrOx film. The reactivity of IrOx towards H₂O₂ oxidation is similar to that seen at Pt, although IrOx has the additional advantages of excellent stability, insensitivity to common interfering substances, biocompatibility and a linear range of detection, up to at least 12 mM H₂O_2. At micromolar concentrations of H₂O₂, a second mode of detection, involving the catalyzed growth of IrOx films at Ir substrates, can be employed. These two methods of H₂O₂ analysis (oxidation/reduction and enhanced IrOx growth) can also be employed for glucose detection using IrOx‐based glucose biosensors.