Examination of in situ Generation of Hydroxyl Radicals and Ozone in a Flow-through Electrochemical Reactor

Generation of hydroxyl radicals and ozone in a low ionic strength influent (0.001 M Na₂SO₄) treated in a continuous flow electrochemical (EC) reactor equipped with a cobalt-promoted lead dioxide anode was examined using p-chlorobenzoic acid (pCBA) and indigotrisulfonate (ITS) probes. EC generation of hydroxyl radicals via the oxidation of water was determined to precede that of ozone. OH· current yields were affected virtually solely by the current density, with almost negligible effects of variations of pH and carbonate concentrations. Absolute values of the current yields of EC generated OH· radicals were close to 1.0% for current densities > 30 mA/cm². The EC generation of ozone was suppressed in the presence of organic species, primarily due to the interception of OH· radicals that react with oxygen to form ozone. Apparent kinetic constants of major reactions associated with the EC generation of ozone were determined based on a steady-state model of an EC-controlled continuous flow reactor.     

Applicability of coumarin for detecting and measuring hydroxyl radicals generated by photoexcitation of TiO2 nanoparticles

Applicability of coumarin (COU) as fluorescent probe to detect and measure hydroxyl radicals generated by UV irradiation of aqueous suspension of TiO₂ was investigated under aerobic and anaerobic conditions. The fluorescent 7-hydroxycoumarin (7HC) was formed in argon-saturated suspension when silver ion was used as electron acceptor. The luminescence intensity increased with irradiation time until the deposition of silver on the surface of TiO₂ was completed and then the luminescence intensity was constant and proportional to the initial concentration of the silver ion. The low yield of 7HC related to the deposited silver (0.32%) indicates the appearance of efficient side reactions of hydroxyl radicals and holes. It has also been demonstrated that efficient electron donors reacting directly with photogenerated holes such as oxalic acid significantly reduce the yield of 7HC. Using oxalic acid of relatively high concentration in aerated suspension leads to the production of hydroxyl radical in thermal reactions followed by primary electron transfer steps.     

Enhancement of Wastewater Disinfection Efficiency in Full-Scale Ozone Bubble-Diffuser Contactors

Tracer and disinfection tests were performed with the ozone bubble-diffuser contactors at the Belmont and Southport Advanced Wastewater Treatment Plants operated by the City of Indianapolis, Department of Public Works. The objective of the study was to develop a better understanding for the role of hydrodynamics and contactor design on the disinfection efficiency achieved in these contactors. Tracer tests were performed at varying gas and wastewater flow rates. The results indicated that high backmixing occurred within each chamber of the over-under ozone bubble-diffuser contactor trains. The addition of three baffles to one of the contactor trains resulted in a decrease in overall contactor backmixing. Low contactor backmixing was observed at high wastewater flow rates combined with high or medium gas flow rates for both the modified and original trains. Monitoring of effluent fecal coliform concentrations for both the original and modified contactor trains revealed lower average concentrations in the modified train effluent as compared to the original train.     

Photocatalytic inactivation of Escherischia coli: Effect of concentration of TiO2 and microorganism, nature, and intensity of UV irradiation

The efficiency of photocatalytic disinfection, used to inactivate Escherischia coli K12 under different physico-chemical parameters, was examined. The photocatalyst chosen was the semiconductor TiO₂ degussa P25 and the irradiation was produced by an HPK 125 lamp. The effect of titania concentration was investigated using two E. coli concentrations. The photocatalyst concentration ranged from 0.1 to 2.5 g/L. The evolution of E. coli inactivation as function of time was discussed depending on the E. coli and TiO₂ concentrations. The optimal concentration of the photocatalyst, 0.25 g/L, is lower than that necessary to absorb all photons and to degrade the organic compounds. Some hypotheses are presented to explain this behaviour. The effect of the different domains of UV light (UVA, UVB, and UVC) was also studied and modification of the light irradiation intensity is discussed. No bacteria photolysis was obtained with UVA but the use UVC had, on the contrary, a detrimental effect on bacteria survival. The addition of titania at a low concentration, 0.25 g/L, improved the inactivation of E. coli in the presence of UVA and UVB, but a detrimental effect was observed under UVC. The disinfection efficiency increases as a function of light intensity, whatever the photocatalytic conditions (different TiO₂ concentrations and different UV domains). No bacterial growth was observed after disinfection, whether the system contained titania or not.     

Influence of Hydrodynamics on Giardia Cyst Inactivation by Ozone. Study by Kinetics and by “CT” Approach

This Research Note deals with the problem of providing appropriate disinfection from one of the most resistant microorganisms (the Giardia cysts) while trying to provide a more strict and logical approach to the “CT” concept. A further discussion of the U.S. Environmental Protection Agency (EPA) disinfection requirements in accordance with the kinetics and hydraulics of the ozonation process will be made in order to reconsider the definition of detention time. The main objective is the comparison of two possible approaches for determination of the disinfection conditions. The first implies consideration of the kinetics and hydraulics of the ozonation process. The second is based only on the hydrodynamics data and the use of an additional hypothesis known as the concept of the “CT” value.     

Generation of oxysterols formed by free radicals and enzymes by electrochemical oxidation

It is commonly accepted that cholesterol oxide derivatives, also named oxysterols, are 27 carbon‐atom molecules deriving either from enzymatic and non‐enzymatic oxidation of cholesterol. Most of these compounds can be synthesized by more or less difficult and time consuming chemical reactions, and some of them have been discovered before the identification of the enzymes [mainly cytochrome P450 enzymes (CYP enzymes)] involved in their biosynthesis. A wide range of biological activities depends on oxysterols. Some oxysterols are also involved in the synthesis of cholesterol metabolites which have various properties. The paper by Weber et al. in this issue of European Journal of Lipid Science and Technology is of interest because it reports that an electrochemical oxidation of cholesterol rapidly generates numerous oxysterols which are usually generated either by enzymatic processes in vivo or under the action of different chemical and physical agents (free radicals, sun light, …) in vivo or not. This has a crucial importance and suggests that the border between enzymatic and non‐enzymatic generation of oxysterols should be reconsidered, at least for some of these compounds. Consequently, these observations may have major chemical and physiopathological significance.     

Study of the coupling reactions between electrochemically generated aromatic radical anions and methyl, alkyl and benzyl radicals

Alkyl radicals produced in the indirect reduction of alkyl halides or alkyldimethylsulfonium salts by electrochemically generated aromatic radical anions couple fast with the latter and alkylated or dialkylated dihydro compounds are formed. Rate constants measured for the coupling reaction between on one hand methyl, primary, secondary and tertiary alkyl radicals as well as benzyl and cumyl radicals and on the other hand a wide spectrum of electrochemically generated aromatic radical anions are found to be about 1×10⁹ M⁻¹ s⁻¹. Previous measurements of coupling rate constants for primary alkyl radicals have been re-evaluated since they were affected by the presence of an S_N2 reaction occurring between the alkyl halides used as radical precursors and the aromatic radical anions. New experiments are also included using alkyldimethylsulfonium salts as precursors in order to prevent such S_N2 artefacts. It is concluded that sterical hindrance does not play a significant role for the radical-radical anion coupling reactions. In general the rate constants for the coupling reactions are all close to 10⁹ M⁻¹ s⁻¹.     

Electrochemical and spectral properties of meta-linked 1,3,5-tris(aryl)benzenes and 2,4,6-tris(aryl)-1-phenoles, and their polymers

We present electrochemical and spectral properties of symmetric monomers 1,3,5-tris(aryl)benzenes and 2,4,6-tris(aryl)-1-phenols and their polymers. These compounds contain thienyl, furyl or EDOT moieties attached to central benzene or phenol ring at the meta-position, synthesized by a Stille cross-coupling procedure. All monomers are electroactive and undergo electropolymerization creating thin films on an electrode surface. Polymers with meta-linkages were obtained by electrochemical oxidation. Detailed cyclic voltammetry and in situ UV-vis spectroelectrochemistry show that polymers with hydroxy groups exhibit higher conductivity and better stability than with benzene core. Interesting and different behavior occurs for 2,4,6-tris(2-thienyl)-1-phenol, for which the characteristic, sharp, redox peak is observed.     

Control of hydroxyl group content in silica particle synthesized by the sol-precipitation process

This study investigated the control of hydroxyl groups, one of key factors determining the surface properties of silica particles synthesized by the sol-precipitation of tetraethyl orthosilicate (TEOS). Thus, a thermal gravity analysis (TGA) was used to facilitate quantitative measurements of the hydroxyl groups on the silica particles, while BET and FT-IR were used to analyze the specific surface area and functional silane groups on the silica particles, respectively. In the sol-precipitation process, silanes that include various hydroxyl groups are formed as intermediates based on the hydrolysis and condensation of TEOS. Thus, NH₃, as a basic catalyst initiating the nucleophilic substitution of TEOS, was found to accelerate the hydrolysis and increase the hydroxyl group content on the silica particles. Plus, the hydroxyl group content was also increased when increasing the concentrations of TEOS and water as the hydrolysis reactants. However, the hydroxyl group content was reduced when increasing the temperature, due to the promotion of condensation. Based on the weight loss of the particles according to the thermal analysis, the hydroxyl group content on the silica particles varied from 5.6–42.7 OH/nm² under the above reaction conditions.     

Oxidation of several chlorophenolic derivatives by UV irradiation and hydroxyl radicals

The oxidation of some chlorophenols: 4‐chlorophenol, 2,4‐dichlorophenol, 2,4,6‐trichlorophenol, 2,3,4,6‐tetrachlorophenol, tetrachlorocatechol (3,4,5,6‐tetrachloro‐2‐hydroxy phenol) and 4‐chloroguaiacol (4‐chloro‐2‐methoxy phenol) has been studied via single photodecomposition produced by polychromatic UV irradiation, oxidation by hydroxyl radicals generated by Fenton's reagent (hydrogen peroxide plus ferrous ions), and degradation by hydroxyl radicals produced by combinations of UV irradiation plus hydrogen peroxide, and UV irradiation plus hydrogen peroxide and ferrous ions (photo‐Fenton system). These organics have been selected as models of chloro‐phenolic derivative pollutants present in wastewaters and groundwaters. The degradation levels obtained in each process are reported. The quantum yields in the single photodecomposition reaction and the rate constants between the chlorophenols and the hydroxyl radicals in the reaction with Fenton's reagent are determined. Finally, the additional contributions to the photodecomposition promoted by the radical reaction in the combined UV/H₂O₂ and photo‐Fenton systems are also evaluated. © 2001 Society of Chemical Industry     

电化学诱发羟基自由基降解水中酚类污染物

DMPO（5,5-dimethyl-1-pyrroline-N-oxide）为自旋捕集剂,采用电子自旋共振技术（electron spin resonance spectroscopy,ESR）直接证实了经氟树脂改性的β PbO₂阳极和不锈钢网阴极构成的电化学体系中产生的羟基自由基（·OH）。通过电化学氧化水中含酚类及其前驱体污染物,发现环状结构化合物受电化学产生的羟基自由基攻击而发生开环反应产生易生物降解的有机酸,如反丁烯二酸和草酸,直至完全矿化为CO₂和水分子,苯醌是酚类污染物开环前产生的共同稳态中间体。该类污染物的电化学降解共性规律为电化学氧化技术的工业化应用和提高其处理工艺的经济性提供了理论依据。     

羟基硅油原位改性制备疏水性沉淀二氧化硅

采用羟基硅油原位改性制备疏水性沉淀二氧化硅。红外光谱（FT-IR）分析表明,羟基硅油通过化学键接枝到二氧化硅表面。扫描电镜（SEM）分析表明,原位改性改善了沉淀二氧化硅的团聚现象,使之分散性提高,与有机基体聚丙烯树脂的相容性增大。疏水性测试表明,羟基硅油203-B和203-D的用量（羟基硅油与原料中二氧化硅的质量比）达到17.9%时,疏水度分别达到24.59%和22.17%,羟基硅油相对分子质量越小,羟基含量越高,改性效果越明显。原位改性使沉淀二氧化硅吸油率降低。     

不饱和羟基脂肪酸原位改性炭黑补强EPDM的结构和形态

测试了三元乙丙橡胶(EPDM)混炼胶的结合橡胶含量，硫化胶的表现交联密度，采用FT-IR表征了不饱和羟基脂肪酸在EPDM硫化胶中的反应，DMTA研究了硫化胶的动态力学性能，SEM观察了EPDM硫化胶中炭黑的表面形貌。结果表明：EPDM混炼胶的结合橡胶含量随着不饱和羟基脂肪酸的加入出现一个峰值，表观交联密度略有下降；不饱和羟基脂肪酸参与了EPDM硫化胶的反应，提高了常温范围内EPDM硫化胶的损耗因子；适量的不饱和羟基脂肪酸可以改善炭黑在EPDM橡胶中的分散。最后提出了一个不饱和羟基脂肪酸补强橡胶的模型，认为不饱和羟基脂肪酸在EPDM硫化胶中起到柔性桥键的作用．阻碍了炭黑聚集体的形成．是硫化胶屈挠疲劳性能显著改善的主要原因。     

Synthesis and properties of cationic photopolymerizable hyperbranched polyesters with terminal oxetane groups by the couple-monomer polymerization of carboxylic anhydride with hydroxyl oxetane

The hyperbranched polyesters with terminal oxetane groups were synthesized via couple-monomer methodology based on carboxylic anhydride and hydroxyl oxetane. Two competitive reactions, ring-opening reaction of carboxylic group with oxetane group and esterification of carboxylic group with hydroxyl group, occurred synchronously during the polymerization. The results showed that the hyperbranched polyesters, poly(SA-EHO) and poly(SA-EHPO), were synthesized successfully when succinic anhydride (SA) was selected to react with 3-Ethyl-3-(hydroxymethyl)oxetane (EHO) and 3-ethyl-3-((4-hydroxymethyl)phenoxymethyl)oxetane (EHPO), respectively. The degree of branching was determined to be about 0.7 for poly(SA-EHO) from the ¹H NMR result, which was higher than those reported in literature, indicating that the esterification was dominant. The glass transition temperatures (T_g)s were measured as −11.5 °C for poly(SA-EHO) and 14.3 °C for poly(SA-EHPO) by DSC. The number average molecular weights were 1914 g/mol and 2108 g/mol with the polydispersity indices of 2.39 and 2.28 for poly(SA-EHO) and poly(SA-EHPO), respectively. Both poly(SA-EHO) and poly(SA-EHPO) were added to bisphenol A epoxy resin, EP828, with different contents and cured under UV exposure. From the DMTA and tensile results, the UV cured poly(SA-EHPO) showed higher T_g and tensile strength compared with poly(SA-EHO) because of the existence of phenyl group in poly(SA-EHPO) chain. Moreover, both the T_gs and mechanical strength decreased, whereas the elongation percents at break increased with poly(SA-EHO) and poly(SA-EHPO) increased. This indicates that the flexibility of cured films was improved by the addition of poly(SA-EHO) and poly(SA-EHPO) in the formulations.     

Mineralization of Para-Chlorobenzoic Acid in Water by Cobalt-Incorporated MCM-41 Catalyzed Ozonation

Cobalt-incorporated MCM-41(Co-MCM-41) was used as a heterogeneous catalyst for the ozonation of para-chlorobenzoic acid (p-CBA) in aqueous solution. Cobalt oxide supported on MCM-41(Co/MCM-41) was synthesized for comparison. Their textural properties were elucidated by various characterization techniques to understand the relationship between surface texture and catalytic activity. TOC removal at 60 min reached 91% with Co-MCM-41, 83% with Co/MCM-41 and only 52% with ozone alone, respectively. Observations from diffuse reflection spectroscopy demonstrated that different metal phases were formed in these cobalt-modified molecular sieves samples. Radical scavenger experiments indicated the formation of hydroxyl radicals that were responsible for the effective degradation of p-CBA. An integrated approach to the catalytic mechanism was proposed by considering the variation of pH in the course of ozonation as well as its subsequent influence on the dissociation of targeted compounds and surface charge of the catalyst. In the reusability experiments, the reused Co-MCM-41 was able to regain the same catalytic capability as the fresh one within 5 cycles. X-ray photoelectron spectroscopy results indicated that a part of Co²⁺ was oxidized to Co³⁺ after oxidation reaction.     

Spontaneous and Electrochemical Reduction of Silver by Polypyrrole Deposits

Abstract

Polypyrrole (ppy) coatings doped with p-toluene sulfonate sodium on stainless steel mesh (SSM) have been electrosynthesized in aqueous solution. The removal of Ag⁺ ions from acidic solutions was investigated through spontaneous reduction (SR) and electrochemical reduction (ER) procedures using reduced composite ppy-SSM. Higher removal efficiencies and current efficiencies were obtained by ER process for ppy-SSM rather than SR process for ppy-SSM and ER process for SSM under comparable conditions. Due to its high efficiency and simplicity, ER was supposed to be an alternative advantageous method for the recovery of low-level silver concentration in industrial wastewater. Cyclic voltammetry was carried out to characterize the electrochemical behavior of ppy-SSM in acid solutions containing Ag⁺. Metallic silver deposited on ppy-SSM has been evidenced by scanning electron microscopy (SEM) analysis.     

Electrochemical synthesis of selenium nanotubes by using CTAB soft-template

The single-crystalline Se nanotubes were synthesized on the surface of Au sheet electrode by cyclic voltammetry. In synthesis process, cetyltrimethyl ammonium bromide (CTAB) was used as soft-template. The formation mechanism of Se nanotubes was discussed. Furthermore, the deposits with other morphologies were also obtained by modulating parameters in the synthesis process. The products as-prepared were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and laser Raman spectrograph (LRS). The electrochemical behavior of the Se nanotubes was studied by the linear scan voltammetry.     

Electrochemical properties of boron-carbon-nitride films formed by magnetron sputtering

The electrochemical behavior of B_1.0C_2.4N_1.0 thin film was investigated in acidic, neutral and alkaline solutions. The anodic polarization curve of the film in 1 M NaOH showed the anodic dissolution of the film. The curve of the film in 1 M HCl showed no anodic dissolution. The cathodic polarization curve in 1 M NaCl showed shift to a negative potential side, but the anodic polarization curve was the same as that of Pt. The anodic dissolution in 1 M NaOH depended on potentials, that is, no anodic dissolution was recognized in a potential range of −0.2 to 0.1 V but the dissolution rate increased with increasing potential in a range of 0.1-0.6 V. The anodic current density of the film is directly proportional to the dissolution rate at potentials higher than 0.1 V. The dissolution rate of the film was increased with increasing solution pH.     

Removal of Tartrazine From Water by Adsorption with Electrochemical Regeneration

An innovative process has been developed at University of the Manchester in order to remove organic contaminants from wastewater using graphite intercalation compounds (GICs) as adsorbents with electrochemical regeneration. The present study has demonstrated the removal of tartrazine, from water by adsorption and electrochemical regeneration. The adsorption of tartrazine onto GIC adsorbent was shown to be a quick process, however, with extremely low adsorption capacity compared to porous adsorbents. Low adsorption capacity of the adsorbent is being compensated by rapid electrochemical regeneration associated with low energy consumption that makes the process cost-effective. Regeneration efficiency of around 100% could be obtained in an electrochemical cell by passing a charge of 18 C g^?1 for 18 min through a 10-mm thick adsorbent bed. A series of adsorption and regeneration cycles showed that there was little loss in adsorbent capacity, demonstrating that tartrazine loaded GIC adsorbent could be effectively regenerated electrochemically.     

Investigation of structure and ORR reactivity of fuel cell catalysts by in-situ STM

In order to provide insight into the interfacial relationships at fuel cell electrodes, a measuring technique based on a scanning tunneling microscope working in an electrochemical cell has been developed. The structure of model electrodes consisting of carbon supported Pt and ionomer mixtures as well as MEA electrode surfaces is imaged by the electrochemical scanning tunneling microscope (EC-STM) from microscale to nanoscale. Images with subnanometer resolution are obtained indicating that some ordering of the particles on the carbon support is present in the model system and in the MEA. It is demonstrated that in both cases nanometer structures can be imaged reliably and that the interface is rather clean and active under reaction conditions. In addition, a technique has been developed to measure the local reactivity by using the STM tip as a sensor electrode for the ORR.