Progress and prospect of anodic oxidation for the remediation of perfluoroalkyl and polyfluoroalkyl substances in water and wastewater using diamond electrodes

Although diamond electrodes are widely used in the field of electroanalysis and sensing, their application in the field of environmental engineering has yet to be fully realized. Many research studies have considered their potential application in water and wastewater treatment, where the in-situ electrochemical process can avoid the need for chemical additives by facilitating the oxidation of pollutants on the electrode surface or mediated by electrochemically synthesized oxidants in solution. Diamond-based electro-oxidation can effectively treat a number of organic micropollutants and is now being evaluated for the abatement of perfluoroalkyl and polyfluoroalkyl substances, which pose health concerns and are ubiquitous recalcitrant environmental contaminants. To move implementation of diamond-based electro-oxidation forward, the integration of modifications and codopants to yield more advanced electrode materials needs to be further developed and understood. The progress and current strategies associated with diamond electrode modifications for perfluoroalkyl and polyfluoroalkyl substances abatement as well as future considerations are discussed.     

Wide-scope screening of polar contaminants of concern in water: A critical review of liquid chromatography-high resolution mass spectrometry-based strategies

The number of chemicals with potential to reach the environment is still largely unknown, which poses great challenges for both environmental scientists and analytical chemists. Liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) is currently the instrumentation of choice for identification of wide-scope polar chemicals of concern (CECs) in water. This review critically evaluates all steps involved in screening for polar CECs in water, including sampling and extraction, analysis by LC-HRMS, data (pre-)treatment, evaluation and reporting. Passive samplers and direct injection, in combination with LC-HRMS, provide new opportunities compared with conventional grab water sampling, as do instrumental advances such as ion-mobility spectrometry coupled to HRMS (IM-HRMS). In this paper, we argue that target, suspect and non-target screening should not be viewed as three separate principles, but rather as conceptual approaches to general data treatment strategies that can be linked together. Due to the large amount of data generated, smart prioritisation strategies are needed, in particular for non-target screening, to reduce complexity and focus on data of high interest. We critically evaluate existing strategies and consider that each prioritisation step will result in data loss (as any other step in a screening study), requiring compromises depending on the research question to be tackled. Many different data treatment strategies have been developed in recent years, but structure elucidation remains a challenging and time-consuming task. We discuss current and potential future trends, e.g. effect-based methods that can be used as future prioritisation tools, technological advances like IM-HRMS and improved software solutions that can enable new data treatment strategies.     

Nanomaterials for electrochemical detection of pollutants in water: A review

The survival of living beings, including humanity, depends on a continuous supply of clean water. However, due to the development of industry, agriculture, and population growth, an increasing number of wastewaters is discarded, and the negative effects of such actions are clear. The first step in solving this situation is the collection and monitoring of pollutants in water bodies to subsequently facilitate their treatment. Nonetheless, traditional sensing techniques are typically laboratory-based, leading to potential diminishment in analysis quality. In this paper, the most recent developments in micro- and nano-electrochemical devices for pollutant detection in wastewater are reviewed. The devices reviewed are based on a variety of electrodes and the sensing of three different categories of pollutants: nutrients and phenolic compounds, heavy metals, and organic matter. From these electrodes, Cu, Co, and Bi showed promise as versatile materials to detect a grand variety of contaminants. Also, the most commonly used material is glassy carbon, present in the detection of all reviewed analytes.     

The reactivity of 2,2"-bipyridine complexes in the electrochemical reduction of organohalides

Nickel(0) complexes coordinatively unsaturated with 2,2"-bipyridine (bpy) are more reactive in the oxidative addition to organic halides than the saturated analogs. -Organonickel complexes formed as intermediates of catalytic cycles were prepared in high yields using nickel complexes coordinatively unsaturated with bpy and aromatic halides containing a methyl group in the ortho-position of the ring.     

Simple preparation and catalytic properties of ZnO for ozonation degradation of phenol in water

ZnO particles about 200 nm were prepared through a facile hydrothermal method.Compared with single ozonation,the degradation efficiency of phenol increased about 23.7%and the degradation efficiency of intermediates improved about four times in the presence of ZnO at 298 K.In addition,the catalyst had good stability in the ozonation process.The influence of temperature was investigated and it was found that the better catalysis efficiency could be obtained at lower temperature.     

A critical review on the electrochemical production and use of peroxo-compounds

Peroxosulfates, peroxocarbonates and peroxophosphates form a group of powerful oxidants that can be synthesized electrochemically and used for the treatment of refractory compounds. Based on the latest studies in the bibliography, this critical review presents the potentialities and also the current limits of the electrosynthesis of these peroxo compounds coupled to their reactions with target compounds. The main parameters such as electrode material, use of additives, cell geometry, temperature and pH affecting the efficiency of the process will be discussed. To conclude, the new challenges and research perspectives in this theme to be performed will be presented before development at an industrial scale.     

Silver embedded C-TiO2 exhibits improved photocatalytic properties with potential application in waste water treatment

Non-metal element doping on photocatalysts demonstrates a wide range of disadvantages. Hence metal embedding on nanomaterials is considered to enhance photocatalytic efficiency. In this study, we employed silver nano particle embedding on C-TiO₂ photocatalyst to improve its phtotocatytic degradation efficiency of organic water pollutant such as methyl orange. Modified sol-gel methods based on self-assembly technique was used to prepare the nanoformulations. The synthesized nanoparticles were characterized by X-Ray diffraction (XRD), Fourier transforms infrared (FT-IR), Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy, and photoluminescence spectra (PL). Compared to non-silver formulation (C-TiO₂), silver embedded nanomaterial (C-TiO₂/Ag) displayed an increased shift in the light absorption towards visible spectrum. A low photoluminescence (PL) intensity by 1 wt% C-TiO₂/Ag indicated improved photocatalytic efficiency. Further, higher degradation of organic dye methyl orange confirmed that 1 wt% C-TiO₂/Ag exhibited the best photodegradation rate over its non Ag embedded C-TiO₂. Embedding of silver on C-TiO₂ extends optical absorption edge of C-TiO₂ to more visible spectrum and inhibits electron-hole recombination resulting in enhanced photocatalytic activity. Photocatalytic degradation on methyl orange organic pollutant was considerably improved indicating its potential use in water treatment applications.     

Double-layer dynamics in the adsorption of tetrabutylammonium ions at the mercury | water interface Part 4. The reduction of hexammine-cobalt(III) through tetrabutylammonium films

The reduction of hexamminecobalt(III) at the mercury-water interface is strongly affected by the presence of a condensed tetrabutylammonium film. When the anions present are fluoride and/or tetrafluoroborate, electron transfer through the film proceeds via an inner-sphere mechanism, i.e. the film must be opened so that hexamminecobalt(III) can make direct contact with the metal. In the presence of bromide anions, an outer-sphere pathway is indicated, probably involving bridging by bromide ions. Unusual current-time transients of the reduction of hexamminecobalt(III) in the presence of tetrabutylammonium ions are correlated with the kinetics of film formation.     

Effective removal of anionic dyes from aqueous solutions by novel polyethylenimine-ozone oxidized hydrochar (PEI-OzHC) adsorbent

The adsorption behavior of the anionic dyes Remazol Brilliant Blue R (RBBR) and Reactive Black 5 (RB5) from aqueous solutions by polyethylenimine ozone oxidized hydrochar (PEI-OzHC) was investigated. The adsorption capacities of both dyes increased with functionalization of PEI in the hydrochar adsorbent. The results of surface characterization (FTIR, BET, TGA, elemental analysis, and SEM) showed that PEI modification greatly enhanced the adsorbent surface chemistry with a slight improvement of adsorbent textural properties. In addition, the adsorption kinetics data showed an excellent adsorption efficiency as reflected in the high removal percentages of the anionic dyes. The Isotherm results indicated that RBBR and RB5 dye adsorption occurred via monolayer adsorption, and chemisorption was the rate-controlling step. The PEI-OzHC adsorbent possesses higher maximum Langmuir adsorption capacity towards RBBR (218.3 mg/g) than RB5 (182.7 mg/g). This increase in adsorption capacity is attributed to the higher number of functional groups in RBBR that interact with the adsorbent. This study reveals the potential use of adsorbents derived from pine wood hydrochar in municipal as well as industrial wastewater treatment. Furthermore, surface chemistry modification is proven as an effective strategy to enhance the performance of biomass-derived adsorbents.     

FTIR spectroscopy study of the electrochemical reduction of CO2 on various metal electrodes in methanol

The electrochemical reduction of CO₂ on Sn, Cu, Au, In, Ni, Ru and Pt electrodes in methanol containing 0.1 M sodium perchlorate was studied by cyclic voltammetry and in-situ FTIR spectroscopy. Dissolved CO₂ increases the cathodic current at potentials below −1.3 V vs. Ag|0.01 M Ag⁺ with Sn, Au, Cu, In and Ni electrodes. It is concluded from the FTIR spectra obtained that there is no reduction of CO₂ on any of the metals studied, and that the only reaction product detected by Fourier transform (FT) IR spectroscopy, i.e. CO²⁻₃, is formed by reaction of CO₂ with hydroxyl anions produced in the electroreduction of residual water.In order to identify the electroreduction products of CO₂ it was necessary to obtain the FTIR spectra of sodium oxalate and sodium carbonate in methanol. They were obtained by the electroreduction of oxalic acid and the alkalinization of CO₂-saturated methanol respectively. It could be proved that the electroreduction of carboxylic acids to carboxylate anions in organic solvents does not require either a H-chemisorbing metal electrode, or the presence of water in the solvent.     

Recent advances in electrochemical water technologies for the treatment of antibiotics: A short review

This short review presents a critical overview of the most recent works published in the literature related to the use of electrochemical advanced oxidation processes (EAOPs) for the treatment of antibiotics present in synthetic and real wastewaters. The first section focuses on novelties within the traditional EAOPs, including electrochemical oxidation and electrochemical Fenton-based processes. The second section is devoted to new electrochemical technologies, including heterogeneous electro-Fenton, electrochemically activated persulfate processes, and combined processes. Future perspectives about these processes are also presented to aid the continuous evolution of research in the area.     

Direct and indirect electrochemical reduction of organic halides in aprotic media

Cyclic voltammetric reduction of 17 different organic halides including alkyl, allyl, and benzyl chlorides, bromides, and iodides in aprotic media (DMF, DMSO, and acetonitrile, AN), containing 0.1 M Bu₄NClO₄, have been reported at glassy carbon (gc) and graphite as working electrodes. A single two-electron irreversible and diffusion-limited reduction of the carbon-halogen bond is observed, the reduction potentials ranging from –1.20 to –2.70 V (versus silver wire quasireference electrode) depending on the halide, the solvent, and the electrode. Indirect reduction of these 17 halides, however, is effected at much lower potentials (–0.79 to –0.92 V versus SCE) depending on the experimental conditions by in situ electrogenerated superoxide ion (O ₂ ^– ) by CPE. The products have been characterized by TLC, GC, CV, or chemical estimation. The diorganic peroxide and the organic hydroperoxide were the major products. In case of tertiary alkyl halides, however, alkenes predominated, due to basic nature of O ₂ ^– in these reactions. These studies indicate sufficient strength of O ₂ ^– as a nucleophile or base depending on the experimental conditions.From Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 350–355.Original English Text Copyright © 2005 by Vasudevan.This article was submitted by the author in English.     

Influence of water filtration on the determination of a wide range of dissolved contaminants at parts-per-trillion levels

The adsorption of dissolved organic contaminants on glass fibre filters throughout water dissolved/particulate phase decoupling studies was examined. A total of 49 different compounds were considered at low concentration levels (ng L⁻¹), including PAHs, PCBs, organochlorine and organophosphorus pesticides, triazines, thiocarbamates, pyrethroids, phosphate esters and caffeine. Their adsorption on the filters was positively correlated with their log Kow and solubilities, indicating that filter adsorption increased with hydrophobicity. The influence of water properties (i.e. salinity and dissolved organic carbon (DOC) content) was also studied by means of a star experimental design (n = 11). Salinity was the main factor in increasing the adsorption, due to the salting out effect. The influence of DOC suggested that part of the contaminant losses during water filtration may have been caused by the retention on the organic matter adsorbed on the filter surface. Nevertheless, a decrease in filter retention was observed for water with the highest DOC contents, which was probably due to an enhancement of the contaminant solubility in these conditions. Although several factors may control the adsorption process in naturally occurring waters, the extent of the retention of dissolved target analytes on the glass fibre filters should not be underestimated in the analysis of hydrophobic contaminants in marine and estuarine waters at very low concentrations (ppt level).     

Palladium catalyzed alkynylation of aryl halides (Sonogashira reaction) in water

The palladium catalyzed alkynylation of aryl halides (Sonogashira reaction) has been achieved in pure water without any additives or phase transfer catalysts. The reaction, which requires only 0.5 mol % of Pd(PPh₃)₄ catalyst, is remarkably fast (30 min at 70 °C) producing high yields of the aryl alkyne products.     

The electrochemical advanced oxidation processes coupling of oxidants for organic pollutants degradation: A mini-review

In this mini-review, the homogeneous and heterogeneous EAOPs-oxidant processes were summarized. The reaction mechanisms of different EAOPs combined with different oxidants are elucidated in detail, as well as the synergistic effect for improving the treatment efficiency.     

Nucleation at three-phase junction lines: in situ atomic force microscopy of the electrochemical reduction of sub-micrometer size silver and mercury(I) halide crystals immobilized on solid electrodes

The electrochemical reduction of sub-micrometer size silver halide crystals immobilized on the surface of gold and platinum electrodes starts at the three-phase junction line where the three phases metal, silver halide and electrolyte solution meet. Following nucleation at this line the reaction advances within seconds on the surface of the silver halide crystals until the entire surface is covered with about 20 atomic layers of silver and the reduction is terminated. The silver layer can be oxidized anodically and the next layer of the silver halide crystals becomes accessible for further reduction. This sequence of reductions and oxidations can be repeated. The nucleation of silver at the three-phase junction line can be detected by atomic force microscopy (AFM) measurements when, after a short reduction pulse and dissolution of the remaining silver halide, a thin ring of silver is observed at the place where the three-phase junction line was situated. The entire scenario of electrochemical reduction of immobilized silver halide crystals depends on the crystal size. Large crystals (about 100 µm edge-length) immobilized on the surface of optically transparent indium tin oxide electrodes show the growing of silver whiskers on the crystal surface, similar to what is known for the reduction of silver halides with photographic developers. However, also in the case of the large crystals, the reduction starts at the three-phase junction line. The electrochemical reduction of immobilized sub-micrometer size crystals of Hg₂Cl₂ and Hg₂Br₂ starts also at the three-phase junction. In the case of gold electrodes the formation of liquid mercury is followed by the formation of a solid crystalline gold amalgam. In the case of platinum electrodes the liquid mercury wets the platinum surface but does not destroy it.     

Light-driven advanced oxidation processes in the disposal of emerging pharmaceutical contaminants in aqueous media: A brief review

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Strategies for the microextraction of polar organic contaminants in water samples

In this paper the most recent developments in the microextraction of polar analytes from aqueous environmental samples are critically reviewed. The particularities of different microextraction approaches, mainly solid-phase microextraction (SPME), stir-bar-sorptive extraction (SBSE), and liquid-phase microextraction (LPME), and their suitability for use in combination with chromatographic or electrically driven separation techniques for determination of polar species are discussed. The compatibility of microextraction techniques, especially SPME, with different derivatisation strategies enabling GC determination of polar analytes and improving their extractability is revised. In addition to the use of derivatisation reactions, the possibility of enhancing the yield of solid-phase microextraction methods for polar analytes by using new coatings and/or larger amounts of sorbent is also considered. Finally, attention is also focussed on describing the versatility of LPME in its different possible formats and its ability to improve selectivity in the extraction of polar analytes with acid-base properties by using separation membranes and buffer solutions, instead of organic solvents, as the acceptor solution.     

A review on catalytic reduction/degradation of organic pollution through silver-based hydrogels

Various challenging pollutants are produced in the environment by organic materials of diverse industries including leather, paint, and textile. Nowadays, it is vital to develop efficient manners regarding the fundamental issues and removing pollutants. Such pollutants can be effectively removed from the environment through heterogeneous catalysts. Recently, a huge deal of interest has been attracted by hydrogel-based metal catalysts as heterogeneous and efficient catalysts. In this regard, silver with its unique features is suitable for environmental remediation. Hence, the present review deals with summarizing the present advances in the synthesis of silver-based hydrogel catalysts, as well as their applications for environmental remediation. Some advantages have been proposed using silver-based hydrogel catalysts suggested including high catalytic ability, reusability, easy work-up, and simple synthesis.     

A simple method for determining water content in organic solvents based on cobalt(Ⅱ)complexes

A method to determine water content in organic solvents was developed based on the color change of cobalt(Ⅱ) nitrate in different solvents.The color-change mechanism and optimal conditions for determining the water content were investigated.The results showed that there was a good linear relationships between the absorbance of cobalt(Ⅱ) complexes in organic solvents and water contents withγin 0.9989～0.9994.This method has the advantages of low cost,good reproducibility,good sensitivity,simple in operation,fast in detection,friendly to the environment and no limitation on linear range for determining water content.It was used to determine water in samples with a satisfactory recovery in 97.81%～101.24%.