High resolution spectrophotometry for identification of chlorine dioxide in concentrated chlorine solutions

Electrolyzed salt brine generators hold great promise for water disinfection in small communities and remote locations. Electrolysis cell liquors have been reported to contain chlorine, chlorine dioxide and ozone. High resolution spectrophotometry was used to observe the presence (or absence) of a unique spectral absorbance pattern present in solutions containing 1-2 mg/l chlorine dioxide.     

High surface area crystalline titanium dioxide: potential and limits in electrochemical energy storage and catalysis

Titanium dioxide is one of the most intensely studied oxides due to its interesting electrochemical and photocatalytic properties and it is widely applied, for example in photocatalysis, electrochemical energy storage, in white pigments, as support in catalysis, etc. Common synthesis methods of titanium dioxide typically require a high temperature step to crystallize the amorphous material into one of the polymorphs of titania, e.g. anatase, brookite and rutile, thus resulting in larger particles and mostly non-porous materials. Only recently, low temperature solution-based protocols gave access to crystalline titania with higher degree of control over the formed polymorph and its intra- or interparticle porosity. The present work critically reviews the formation of crystalline nanoscale titania particles via solution-based approaches without thermal treatment, with special focus on the resulting polymorphs, crystal morphology, surface area, and particle dimensions. Special emphasis is given to sol-gel processes via glycolated precursor molecules as well as the miniemulsion technique. The functional properties of these materials and the differences to chemically identical, non-porous materials are illustrated using heterogeneous catalysis and electrochemical energy storage (battery materials) as example.     

Inorganic by-products in waters disinfected with chlorine dioxide

The continuing diminishing sources of fresh waters has stimulated the search for unconventional water resources, such as effluents from municipal sewage treatment plants, which can be reused for purposes of irrigation in agriculture, cooling water in industry, groundwater aquifer recharge and in the long term even for drinking water. The main problem of using effluents is the presence of pathogenic bacteria and viruses that can affect human and animal health. Therefore, disinfection has been used for many years to control and reduce waterborne diseases.At the moment, most water treatment plants use sodium hypochlorite as their primary biocide. However, the toxicity of chlorinated organic compounds produced during the treatment has led to increased interest in the use of alternative agents. One possible candidate as viable substitute of free chlorine is chlorine dioxide. Before this disinfectant can be recommended for routine use, it is imperative that its safety be assessed.In this research we have investigated the presence of chlorite and chlorate in sewage disinfected with chlorine dioxide. The effect of initial concentration of biocide and contact time was evaluated using a pilot plant fed with the effluent of a municipal treatment plant. Moreover, the influence of ClO₂ generator performance was analyzed and discussed.     

Use of low current densities in electrolyses with conductive-diamond electrochemical — Oxidation to disinfect treated wastewaters for reuse

In the search for new disinfection technologies for reused water, in this work the effect of current density on the disinfection capability, during the electrolyses with conductive diamond anodes of the effluent of a municipal wastewater treatment plant was evaluated. It was found that this electrolytic technology can disinfect completely for current densities ranging from 1.3 to 130 A m^{− 2}, but the disinfection rate and chlorine speciation are significantly affected by particular current density applied. In order to avoid the occurrence of non desired species, the lower value of this range is proposed. In those conditions, complete disinfection can be obtained and hypochlorite and chloramines are the main species, not being produced chlorate, perchlorate or organo-chlorinates species.     

饮用水消毒副产物及其分析技术

介绍了饮用水中液氯、臭氧、二氧化氯消毒副产物的特性和现状,总结了近年来消毒副产物分析领域中常用的各种样品前处理技术及检测方法,展望了今后研究的发展方向.     

Mass spectrometry in the study of mechanisms of aquatic chlorination of organic substrates

Chlorination is an effective method of water disinfection. However, it has been identified as contributing to the formation of a wide variety of disinfection by-products that have been associated with adverse health effects. Natural humic matter and anthropogenic pollutants are responsible for the formation of these by-products. Mass spectrometry is the most efficient tool to analyze the rates of conversion, the nature and levels of by-products in the reactions of chlorinating agents with model organic compounds. More than 30 substrates with various functional groups were studied, while gaseous chlorine and sodium hypochlorite were used as chlorinating agents. The effects of pH, substrate/active chlorine ratio, addition of metal cations and bromides and iodides on the aqueous chlorination process of various organic substrates were investigated. Transformation schemes were proposed for the studied compounds.     

A comparative study on direct and indirect electrochemical oxidation of polyaromatic compounds

This study has been performed to investigate the treatment of an industrial wastewater containing naphthalene- and anthraquinone-sulfonic acids, by direct and indirect electrolyses. The direct electrochemical oxidation has been carried out using boron-doped diamond and lead dioxide anodes, while the indirect electrolyses has been mediated by active chlorine electrogenerated on a platinum anode, or by hydrogen peroxide electrogenerated on a graphite felt cathode. For each type of electrolyses the effects of operating parameters, such as anode material, current density, chloride concentration, ferrous ions concentrations have been also investigated. Measurements of Chemical Oxygen Demand (COD) and colour fading have been used to compare the results of different electrolyses. Experimental data showed that the complete COD and colour removals have been obtained only by direct oxidation or by active chlorine mediated electrolyses. On the contrary using electrogenerated hydrogen peroxide the solution has been presented a residual COD and colour. In particular, it found that faster oxidation rate has been obtained by direct oxidation using a boron-doped diamond anodes at low current density.     

Environmental Fate of Organic Sunscreens during Water Disinfection Processes: The Formation of Degradation By-Products and Their Toxicological Profiles

The development of any commercial product should also be aimed at reducing the risk associated with it, according to the safe-by-design concept; that is, risk assessment should always be at the center of the design, and the impact on human and environmental health should be assessed and eliminated during the product development phase and not afterwards. Unfortunately, even today, most operators in any production sector implement the philosophy of “risk management” or rather of managing the problem when it occurs, using spot interventions instead of changing the approach. This argument is also valid in the production of solar filters, which have reached a satisfactory degree of efficiency in the face of a substantial underestimation of the risks associated with their possible environmental fate. In fact, solar filters have been found in bathing waters and their environmental fate may depend on various factors such as the pH of the water, the presence of organic material, metal ions and light, and, above all, the chemical agents used in the disinfection of the water itself. Thus, during disinfection processes, the generation of dozens of products with a lower molecular weight and generally of an aromatic nature has been tested, where some of them did not receive an exact structural definition and a precise evaluation of their precise toxicological profile. Therefore, it is interesting to draw a complete picture of organic sunscreens and of the byproducts obtained under different conditions and their related ecotoxicological profile.     

The determination of iodine in biological and environmental standard reference materials

Iodine is an element with excellent intrinsic sensitivity when determined by thermal neutron activation. However, in most real samples, the preponderance of chlorine and bromine, relative to iodine, makes the direct determination of iodine virtually impossible. Over the past 20 years, there probably have been as many publications on the separation of iodine as there have been for any other radionuclide. Upon review, however, the methods are essentially the same. After irradiation, the samples are subjected to a rapid destructive process to free the iodine from the matrix and then the iodine is separated from the other halides either by liquid-liquid extraction or by liquid ion exchange. Both of these procedures are, however, rather complex and do not effect a complete separation of the halides in one pass. In the work presented here, a simple procedure is described for the quantitative separation of iodine from chlorine. The procedure utilizes a gas phase separation on hydrated manganese dioxide with iodine collected on silvered quartz wool. The described procedure has been used for the determination of iodine in numerous new and old SRM's at the NBS.     

Electrochemical alternatives for drinking water disinfection

Chlorination is the most common method worldwide for the disinfection of drinking water. However, the identification of potentially toxic products from this method has encouraged the development of alternative disinfection technologies. Among them, electrochemical disinfection has emerged as one of the more feasible alternatives to chlorination. This article reviews electrochemical systems that can contribute to drinking water disinfection and underscores the efficiency of recently developed diamond films in chlorine-free electrochemical systems.     

电子活度和pH对二氧化氯制备和稳定性的影响

建立了氯体系电子活度（pε）和pH优势区域图（pε-pH）图,从酸化、氧化和还原的角度,探讨了标准状态下pε和pH对二氧化氯制备和稳定性的影响。实际生产不可能制备绝对纯净的二氧化氯。对于不同的水体,由于其pε和pH值不同,因而可能使二氧化氯表现出不同的稳定性特征。如果水溶液中二氧化氯不歧化为氯酸根,二氧化氯相对稳定,并与亚氯酸根、氯分子或氯离子稳定共存。当氯体系实现最终平衡时,二氧化氯仅在强酸介质中优势存在,随着酸度降低,二氧化氯歧化为氯酸根和氯气,水溶性和二氧化氯在常规pH条件下不稳定。     

二氧化氯在油田污水处理中的应用研究

由于二氧化氯具有良好的氧化杀菌作用,可以有效地去除油田污水中铁、硫等具有腐蚀性和结垢性的还原性物质,以及杀灭油田污水中的各种细菌。本文考察和报告了二氧化氯在中原油田注水采油废水的应用结果,并展望了它在油田注水采油中应用前景。     

Rapid Determination of HAAs Formation Potential of the Reaction of Humic Acid with Chlorine or Chlorine Dioxide

On the basis of gas chromatography(GC) coupled with a short capillary column and an electron capture detector(ECD), a simple and rapid method for the determination of five haloacetic acids(HAAs) in drinking water was developed by the optimization of derivation conditions and the modification of gas chromatographic program. HAAs formation potential(HAAFP) of the reaction of humic acid with chlorine was determined via this method. The major advantages of the method are the simplicity of chromatographic temperature program and the short run time of GC. Dichloroacetic acid(DCAA) and Trichloroacetic acid(TCAA), which were detected in the determination of HAAFP, were rapidly formed in the first 72 h of the reaction of humic acid with chlorine. HAAFP of the reaction of humic acid with chlorine increased with the increase in the concentrations of humic acid and chlorine. The average HAAFP of the reaction of humic acid with chlorine was 39.9 μg/mg TOC under the experimental conditions. When the concentration of humic acid was 4 mg/L, the concentration of HAAs, which were produced in the reaction of humic acid with chorine, may exceed MCL of 60 μg/L HAAs as the water quality standards for urban water supply of China and the first stage of US EPA disinfection/disinfection by-products(D/DBP) rule; when the concentration of humic acid was 2 mg/L, the concentration of HAAs may exceed MCL of 30 μg/L HAAs for the second stage of US EPA D/DBP rule. When humic acid was reacted with chlorine dioxide, only DCAA was detected with a maximum concentration of 3.3 μg/L at a humic acid content of 6 mg/L. It was demonstrated that the substitution of chlorine dioxide for chorine may entirely or partly control the formation of HAAs and effectively reduce the health risk associated with disinfected drinking water.     

钯基纳米材料电化学还原二氧化碳研究进展

电化学二氧化碳还原是利用电能驱动将CO_2高效转化为小分子碳基燃料的新方法,被认为是目前最具应用潜力的碳资源转化技术之一。然而,CO_2还原反应仍面临着诸多挑战,如反应过电位高,产物选择性低以及析氢反应的竞争等。因此,开发高效的电催化剂是发展CO_2还原技术的核心关键。近年来,Pd基材料在CO_2还原反应中表现出独特的催化性能优势:它不仅可以在接近平衡电位下高选择性地还原CO_2生成甲酸/甲酸盐,还能够在一定的负电位区间高效地还原CO_2生成CO。尽管如此,Pd基材料目前仍存在着成本较高、活性不理想以及稳定性差等问题,严重制约了其进一步应用与发展。对此,本文首先简单介绍了CO_2RR的基本原理,并综述了近年来Pd基催化剂电还原CO_2的应用研究及发展现状。重点探讨了尺寸效应、形貌效应、合金效应、核壳效应及载体效应等对Pd基催化剂性能的影响。最后针对这类材料的问题挑战及其未来发展方向进行了探讨与展望。     

Electrochemical sensing of gases based on liquid collection interfaces

Although many electrochemical gas sensors have been reported, electrochemical gas sensors based on liquid collection constitute a smaller subset. Minimally, a liquid interface based electrochemical gas sensor is composed of two electrodes and an ion conducting electrolyte. There is a large number of possible arrangements of these parts, and many choices exist for their composition and preparation methods. This results in a diverse and rich technology now available for gas sensing. The measurement of some analyte gases of interest, notably ozone, nitrogen oxides, hydrogen peroxide, formaldehyde, ammonia, sulfur dioxide and hydrogen sulfide are specifically discussed. Finally, the recent reviews that are likely to be the most relevant to the further development of electrochemical detection approaches for gases with a liquid collection interface are cited and discussed.     

Application of an amperometric sensor to in-line monitoring of pulp bleaching with chlorine dioxide

Chlorine dioxide is replacing chlorine as the active compound in pulp bleaching in order to reduce the amount of chlorine used in the process and hence also in the waste waters. In bleaching with chlorine dioxide part of the effective bleaching chemical is usually chlorite. The electrochemistry of chlorine dioxide and chlorite at solid electrodes was studied by cyclic voltammetry at different pH values. The observed voltammograms indicated that reduction of chlorine dioxide gives chlorite and oxidation of chlorite gives chlorine dioxide. Both voltammograms were well developed, indicating a reversible process. Both platinum and glassy carbon were used as the working electrode. The dependence of the limiting current of chlorine dioxide and chlorite on pH was studied at both electrodes. The method was tested in the chlorine dioxide bleaching stage D1 in a typical bleaching process. A good correlation was found between the concentrations of chlorine dioxide and chlorite measured by the in-line amperometric method and a standard titrimetric method.     

Evaluation of chlorinated by-products in drinking waters of Central Friuli (Italy)

Drinkable water supplied by aqueducts undergoes preliminar potabilization which, in Italy, is mainly accomplished by chlorine addition. The bactericidal action involved in this process is always accompanied by chlorination and oxidation of organic species (mainly humic and fulvic acids) naturally present in treated waters, so that many disinfection by-products (DBPs) are formed, such as trihalomethanes (THMs) and halo-acetic acids (HAA), which can represent a chemical risk for public health. The aim of this study was the monitoring of DBPs in drinking water disinfected by chlorination, supplied by four different aqueducts of Central Friuli (Italy). DBP evaluations were performed in water samples consisting of both input and output of disinfection plants. The results of analytical determinations were worked out to provide the THM and HAA parameters for disinfected waters, while in feeding waters the following different conventional parameters were adopted: (i) trihalomethanes formation potential (THMFP), (ii) halo-acetic acids formation potential (HAAFP) and (iii) UV absorbance at 254 nm (UV254). The quite moderate content of chlorinated products found in all samples considered highlighted the excellent quality of potabilized waters available in Central Friuli. Moreover, our results confirmed that the majority of DBPs formed when chlorine is used for water disinfection consists of THMs, while chlorites and chlorates prevailed when potabilization is accomplished by using chlorine dioxide. Finally, simple UV254 monitoring turned out to be a profitable approach for the determination of chlorinated by-products only when THMs prevail among DBPs.     

氯酸钾二氧化锰实验室制氧法探原

Oxygen preparation by potassium chlorate and manganese dioxide is one of the most classical laboratory method. Few study has been made so far on its origination and establishment. Through checking the original roles of potassium chlorate and manganese dioxide, it is found that manganese dioxide was ever first selected as raw material for making oxygen, then led the discovery of chlorine by Scheele and potassium chlorate by Berthollet. Potassium chlorate itself was also ever used for oxygen preparation at a high temperature. In 1832, manganese dioxide was firstly mixed with potassium chlorate for oxygen by Döbereiner and reduces the temperature dramatically. With more following studies, the classic method of oxygen preparation via the two materials was finally established.     

二氧化碳电还原制草酸研究进展

近年来, 二氧化碳过量排放所引发的全球变暖等气候问题引起了全世界的广泛关注, 碳减排已成为人类社会可持续发展面临的共同挑战. 利用电化学方法将二氧化碳转化为高附加值化学品是实现碳减排和二氧化碳高附加值利用的理想途径之一, 但仍面临能耗高、 二氧化碳转化率低、 产物选择性差和难分离等问题. 本文以电还原二氧化碳制草酸为例, 从反应机理、 催化剂、 电解液、 催化电极及反应器等方面介绍该反应的研究进展, 对当前二氧化碳电还原制草酸存在的关键问题进行了分析, 并对其未来研究方向进行了展望.