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Direct And Mediated Anodic Oxidation of Organic Pollutants
Abstract
A study was conducted to demonstrate direct and mediated anodic processes for the oxidation of organic pollutants. The study proposed different expressions of current efficiency, such as instantaneous current efficiency (ICE), electrochemical oxidation index (EOI), general current efficiency (GCE), and mineralization current efficiency (MCE). ICE of electro-oxidation was determined by the oxygen flow rate (OFR) method or chemical oxygen demand (COD). GCE represented an average value of current efficiency between the initial time t = 0 and t. Efforts were made to perform electrolysis at a high anodic potential in the region of water discharge, using intermediates of electrogenerated hydroxyl radicals. Another strategy involved oxidizing pollutants by indirect electrolysis, generating a redox reagent in situ as a chemical reactant.
... As can be seen in Figure 4C, the network map of co-citation reference consists of 214 nodes and 3608 links. The largest node is related to the most co-cited reference by Paniza (2009) [49] which had a citation count of 85. The second largest node corresponds to Martnez-Huitle CA (2006) [50] (citation count of 66), followed by Zhang LC (2014) [51] (citation count of 61), and Boggs (2009) [52] (citation count of 40). ...
... Among the top 10 authors or references co-cited, the first-ranked authors Cominelis and Vantharathiam are leading researchers who have made enormous contributions to the explanations of the mechanisms of electrochemical oxidation. In the references with the highest number of co-citations by Paniza [49] and Martinez [50], otherwise, (close associates of Comninellis), Comininelis is cited as the one who explained the anodic material influence on the mechanism degradation of the organic pollutants using electrochemical oxidation. On the other hand, Vedharathinam [53] in the article from 2012 first described the mechanism of urea electro-oxidation on an Ni anode. ...
... Co-citation network map (A) author, (B) top 10 authors, (C) co-citation reference, and (D) top 10 co-citation references[31,[49][50][51][52][53][54][55][56][57]. ...
Last decade, a growing emphasis on developing sustainable and environmentally friendly technologies for electro-oxidative wastewater treatment has catalyzed innovation and spurred research efforts worldwide. Researchers may explore the use of renewable energy sources to drive electrochemical processes, as well as the development of eco-friendly electrode materials for wastewater treatments. The integration of nanostructured anodes into the electrolytic system for wastewater treatment has led to significant advancements in the removal of pollutants via electro-oxidation. Despite the great number of research articles related to the development and use of nanostructured anodes for electro-oxidative wastewater treatment, to our knowledge, no bibliometric analysis has been published in this domain. Therefore, this work presents a bibliometric study of publications on the designated theme, retrieved from the Web of Science Core Collection database, which were published over the last decade. The visual and network analysis of co-authorship among authors, organizations, countries, co-citation of authors, citation of documents and sources, as well as the co-occurrence of author keywords was performed using two compatible pieces of scientometric software, namely VOSviewer (version 1.6.18) and CiteSpace (version 6.2.R4). From 2013 to 2023, there has been a gradual increase in the number of publications regarding the development and use of nanostructured anodes for electro-oxidative wastewater treatment. It suggests a steady advancement in this field. The People’s Republic of China emerges as the most productive country, and it is a leader in international collaborations. Also, the United States of America, South Korea, and European Union countries have significant impacts on the research in this domain. The development and application of nanostructured materials for urea electro-oxidation is a main and prospective research theme. This bibliometric analysis allowed for the visualization of the present landscape and upcoming trends in this research field, thereby facilitating future collaborative research endeavors and knowledge exchange.
... The removal of HCHs can occur by the direct oxidation of the pollutants on the anode surface or by indirect oxidation via hydroxyl radicals electrochemically generated from water oxidation over the BDD anode (Eq. (3)) (Panizza and Cerisola, 2009). Furthermore, the DNAPLsaturated groundwater contains inorganic ions that can be oxidised on the anode surface, favouring the production of powerful oxidants in the aqueous phase. ...
... (9)- (14)) . It is important to note that the electrogenerated free radicals present a higher oxidation potential and also contribute to the degradation of organic pollutants (Panizza and Cerisola, 2009;Wang and Wang, 2020). Low current densities promote the degradation of organics by direct oxidation whereas the application of higher current densities favours mediated oxidation of pollutants via electrogenerated oxidants (Panizza and Cerisola, 2009). ...
... It is important to note that the electrogenerated free radicals present a higher oxidation potential and also contribute to the degradation of organic pollutants (Panizza and Cerisola, 2009;Wang and Wang, 2020). Low current densities promote the degradation of organics by direct oxidation whereas the application of higher current densities favours mediated oxidation of pollutants via electrogenerated oxidants (Panizza and Cerisola, 2009). Both oxidation mechanisms can simultaneously occur during the treatment of groundwater, although direct oxidation is expected to be boosted at 5 and 10 mA cm − 2 , whereas mediated oxidation is enhanced when working at current densities higher than 25 mA cm − 2 . ...
... Although IrO2 can generate hydroxyl radicals from water oxidation following reaction (3), those are stabilized on the electrode surface as chemisorbed superoxides following reaction (4) [35]. The IrO3 superoxide is a weak oxidant that is unable to efficiently oxidize TC leading to only partial oxidation as described by reaction (5) [36]. This characteristic makes IrO2 an active anode material, however, it is still commonly utilized in electrified technologies due to its low cost compared to other electrocatalytic materials such as boron-doped diamond (BDD) [37][38][39]. ...
... Although IrO 2 can generate hydroxyl radicals from water oxidation following reaction (3), those are stabilized on the electrode surface as chemisorbed superoxides following reaction (4) [35]. The IrO 3 superoxide is a weak oxidant that is unable to efficiently oxidize TC leading to only partial oxidation as described by reaction (5) [36]. This characteristic makes IrO 2 an active anode material, however, it is still commonly utilized in electrified technologies due to its low cost compared to other electrocatalytic materials such as boron-doped diamond (BDD) [37][38][39]. ...
This study explores the use of the iron-containing metal–organic framework (MOF), Basolite®F300, as a heterogeneous catalyst for electrochemically-driven Fenton processes. Electrochemical advanced oxidation processes (EAOPs) have shown promise on the abatement of recalcitrant organic pollutants such as pharmaceuticals. Tetracyclines (TC) are a frequently used class of antibiotics that are now polluting surface water and groundwater sources worldwide. Acknowledging the fast capability of EAOPs to treat persistent pharmaceutical pollutants, we propose an electrochemical Fenton treatment process that is catalyzed by the use of a commercially available MOF material to degrade TC. The efficiency of H2O2 generation in the IrO2/carbon felt setup is highlighted. However, electrochemical oxidation with H2O2 production (ECO-H2O2) alone is not enough to achieve complete TC removal, attributed to the formation of weak oxidant species. Incorporating Basolite®F300 in the heterogeneous electro-Fenton (HEF) process results in complete TC removal within 40 min, showcasing its efficacy. Additionally, this study explores the effect of varying MOF concentrations, indicating optimal removal rates at 100 mg L−1 due to a balance of kinetics and limitation of active sites of the catalysts. Furthermore, the impact of the applied current on TC removal is investigated, revealing a proportional relationship between current and removal rates. The analysis of energy efficiency emphasizes 50 mA as the optimal current, however, balancing removal efficiency with electrical energy consumption. This work highlights the potential of Basolite®F300 as an effective catalyst in the HEF process for pollutant abatement, providing valuable insights into optimizing electrified water treatment applications with MOF nanomaterials to treat organic pollutants.
... In both cases, organic substances are oxidized and decomposed into nontoxic and harmless substances. [12][13][14] For the instance of direct oxidation by metal oxide (MO x ) anodes, oxidation of pollutants occurs at the anode surface via direct electron transfer, which is before the oxygen evolution reaction (Equation (1)); the degradation process of indirect oxidation can be expressed as follows: [15][16][17] strong oxidants such as ·OH radicals are in situ generated (·OH, E°(OH/H 2 O) = 2.8 V/standard hydrogen electrode (SHE)) in bulk from water oxidation to form either physisorbed MO x (·OH) or chemisorbed MO x þ 1 on the anode surface, depending on the nature of anode materials (Equation (2) and (3)). ...
... Ti/IrO 2 • High chemical and physical stability • Low oxygen/chlorine evolution potential [64] • Electrode works at low voltage for high electrochemical activity toward oxygen evolution (1.6 V vs normal hydrogen electrode) [184] • Low oxidation activity toward oxidation of substances in water [66,184] • Achieving efficient and long-life electrodes remains a huge challenge Ti/RuO 2 • Low cost, good dimensional stability, and higher OEP (1.9 V) • High efficiency under strongly acidic conditions • High chemical and mechanical resistant • High electrocatalytic activity for generation of strong oxidants (Cl⋅, ⋅OH, [67][68][69][70] • Low service life [71] • Low specific surface area [72] Ti/PbO 2 • Low cost and high electrical conductivity • High OEP (>1.8 V) [15] • Good corrosion resistance [185] and chemical inertness [186] • Poor performance in wastewaters comprising chlorides and inability to resist corrosion [68] • PbO 2 active layer of Ti/PbO 2 is easily exfoliated from the surface of the Ti substrate, especially in sulfuric acid systems, and lead leaching occurs, [69] which leads to poor stability and activity and short electrode life [185,186] Ti/Sb-SnO 2 • Low cost, toxicity, and corrosion resistance • High electrocatalytic activity [110] High OEP (>1.8 V) [187] • High resistivity and short service lifetime [187] Ti/TiO 2 • Good orientation, high mechanical strength, and large specific surface area [80] • Unique unidirectional electron pathway [129] • Semiconducting properties, the poor electrical conductivity [164] www.advancedsciencenews.com www.aem-journal.com voltammetry (LSV) and cyclic voltammetry (CV) tests in Figure 2f,g show that Ti/Ta 2 O 5 -IrO 2 electrode had higher OEP and larger electrochemical effective surface area (consistent with the SEM image). ...
Emerging organic pollutants and refractory pollutants in water bodies have caused severe harm to the ecological environment and human health. Electrochemical advanced oxidation processes (EAOPs) are currently one of the most effective oxidation methods to deal with refractory organic pollutants. Electrode materials serve as the most critical component in influencing the EAOP performance. Dimensionally stable anodes (DSAs) have the advantages of dimensional stability, structural diversity, chemical stability, low oxygen evolution potential and long service life, etc. Herein, several types of Ti‐based metal oxide DSAs (Ti/MOx DSAs) commonly used in EAOPs in the past 5 years, including Ti/IrO2, Ti/RuO2, Ti/PbO2, Ti/Sb–SnO2, and Ti/TiO2, are introduced. The modification methods including metal doping, composition adjustment, nanostructure construction, introduction of intermediate layers, compositing with carbon materials, and formation of 3D structures as well as the applications of these modified Ti‐based DSAs in EAOP for the rapid degradation of various organic pollutants are summarized and their advantages and current shortcomings of electrodes are pointed out. Finally, the Ti‐based DSA's current limitations and future development prospects are concluded.
... Among these, electrocatalysis, particularly electrochemical catalytic oxidation, has garnered significant attention in the field of electrochemical oxidation (Wei et al. 2017). It proceeded, on the one hand, through a nonradical pathway, involving direct electron transfer processes where pollutants acted as either electron donors or acceptors, undergoing direct oxidation or reduction (Panizza & Cerisola 2009). Additionally, indirect oxidation of pollutants occurred in the solution or around the electrode through the presence of oxidants such as singlet oxygen and ozone (Liu et al. 2019). ...
... (4) Ions present in the solution were converted to weaker oxidants (Panizza and Cerisola 2009). ...
Electrocatalytic methods are valuable tools for addressing water pollution and scarcity, offering effective pollutant removal and resource recovery. To investigate the current status and future trends of electrocatalysis in wastewater treatment, a detailed analysis of 9417 papers and 4061 patents was conducted using scientometric methods. China emerged as the leading contributor to publications, and collaborations between China and the USA have emerged as the most frequent partnerships. Primary article co-citation clusters focused on oxygen evolution reaction and electrochemical oxidation, transitioning towards advanced oxidation processes (“persulfate activation”), and electrocatalytic reduction processes (“nitrate reduction”). Bifunctional catalysts, theoretical calculations, electrocatalytic combination technologies, and emerging contaminants were identified as current research hotspots. Patent analysis revealed seven types of electrochemical technologies, which were compared using SWOT analysis, highlighting electrochemical oxidation as prominent. The technological evolution presented the pathway of electro-Fenton to combined electrocatalytic technologies with biochemical processes, and finally to coupling with electrocoagulation. Standardized evaluation systems, waste resource utilization, and energy conservation were important directions of innovation in electrocatalytic technologies. Overall, this study provided a reference for researchers to understand the framework of electrocatalysis in wastewater treatment and also shed light on potential avenues for further innovation in the field.
... Another relevant aspect of electro-Fenton process relates to the electrode material used in the mechanism for the hydroxyl radical production. Indeed, these reactive species are usually produced by water discharge at anode surface using anodes with a high overpotential for oxygen evolution reaction [19]. Among them, boron-doped diamond (BDD) is one of the best performing materials due to its high overpotential (2.30 V) [19]. ...
... Indeed, these reactive species are usually produced by water discharge at anode surface using anodes with a high overpotential for oxygen evolution reaction [19]. Among them, boron-doped diamond (BDD) is one of the best performing materials due to its high overpotential (2.30 V) [19]. Nevertheless, the high cost (> 10 4 $ m −2 ) limits its utilization. ...
Erythrosine B (EB) is a dye widely used in the food and textile industries. Despite many studies that have been proposed in the literature about the electrochemical oxidation of dyes, few studies considered such recalcitrant xanthene compound, although it has been recognized as a threat to health and the environment. Then, this study investigates the oxidation of EB by a homogeneous electro-Fenton process using iron (II) sulfate heptahydrate as a catalyst, carbon felt cathode, and Ti/RuO2 anode. The treated synthetic wastewater contains 100 mg L−1 of EB and has a pH = 3. The effects of three independent variables have been considered for process optimization, such as applied current intensity (0.1–0.5 A), iron concentration (1–10 mM), and stirring rate (100–1000 rpm). Their interactions were investigated considering response surface methodology (RSM) based on Doehlert design as optimization method. EB removal efficiency and energy consumption were considered as model responses after 30 min of electrolysis. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.9819), adj-R2 (0.9276), and low Fisher probability (< 0.0181) for the EB removal model, and R2 (0.9968), adj-R2 (0.9872) and low Fisher probability (< 0.0014) relative to the energy consumption model, suggesting a robust statistical significance. The energy consumption model significantly depends on current density, as expected. The foregoing results obtained by RSM led to the following optimal conditions for EB degradation: current intensity of 0.2 A, iron concentration of 9.397 mM, and stirring rate of 500 rpm, which gave a maximum decolorization rate of 98.15% with a minimum energy consumption of 0.74 kWh m−3 after 30 min of electrolysis. The competitiveness of the electro-Fenton process has been confirmed by the literature analysis proposed as well as by the preliminary economic analysis proposed in the second section of the study.
... The BDD anode is characterized by a high O2 evolution overvoltage (around 2.2 V vs SHE for BDD). BDD has proven to be the most effective material for the anodic oxidation of refractory organic pollutants (Panizza and Cerisola, 2009;Olvera-Vargas et al., 2021;Oturan, 2021), and the use of BDD as an anode in the electro-Fenton process has been shown to significantly improve the efficiency of the process (Oturan et al., 2012;Ridruejo et al., 2018;Olvera-Vargas et al., 2021). ...
In this study, the removal of moxifloxacin, an antibiotic of the fluoroquinolone group, from aqueous solutions was investigated using the electro-Fenton process. As the efficiency of the electro-Fenton process is highly dependent on the amount of H2O2 produced during process, the formation of H2O2 under acidic conditions was also investigated. In this context, the effects of applied current, cathode type and O2 flow rate on H2O2 production were investigated using boron-doped diamond anode. The highest H2O2 production was achieved using the boron-doped diamond anode and the graphite felt cathode. In addition, the optimum conditions for the applied current and oxygen flow rate for H2O2 production were determined to be 0.25 A and 0.1 L min−1, respectively. The effects of applied current and Fe2+ concentration in the electro-Fenton process on the removal of moxifloxacin were investigated. It was found that the moxifloxacin removal rate increased with increasing applied current. The highest H2O2 accumulation was observed at 0.25 A applied current, and moxifloxacin removal also reached 93.6% after 60 min. The moxifloxacin removal rate reached the highest value at Fe2+ concentration of 0.01 mM. This study provides promising results for the efficient treatment of moxifloxacin-containing wastewater by the electro-Fenton process without the addition of H2O2 using boron-doped diamond anode anode and graphite felt cathode.
... Some of these pollutants are teratogenic, mutagenic, and carcinogenic, posing serious health risks. [294] Furthermore, some organic pollutants can undergo chemical reactions in the environment and be transformed into more harmful secondary pollutants. [291] Adsorption is an attractive method for eliminating organic pollutants from intricate ecological environments. ...
... The electrochemical oxidation of dyes from wastewater has shown promising degradation results to eradicate these contaminants in a short period when compared to conventional methods (Rodríguez-Narváez et al. 2021;Wang et al. 2020;Pieczyńska et al. 2019;Martínez-Huitle and Panizza 2018). In the direct oxidation method, the pollutant is first adsorbed on the anode and then oxidized by a powerful oxidant such as the hydroxyl radical or chlorine/hypochlorite ion through the transmission of the anodic electron (Stupar et al. 2017;Zhang et al. 2014;Panizza and Cerisola 2009). Several research has been conducted based on the current literature to remove synthetic colored dyes from water using an electrochemical technique at various electrodes. ...
This contribution describes the indirect electrochemical oxidation of wastewater laden with bromothymol blue and methyl red dyes using a laboratory-scale electrochemical reactor with a Ti/Ru0.3Ti0.7O2 anode and stainless-steel cathode. The influence of current density, pH, and electrolyte concentrations on the oxidative degradation pattern of the dyes in the wastewater was also investigated by coupling the electrochemical reactor with an Ultraviolet–Visible spectrometer. By indirect oxidation, 97% of the bromothymol blue at 10 mA cm–2 current density and pH 3.0 and 98% of the methyl red at 2 mA cm–2 current density at pH 3.0 were indirectly oxidized in 10 min Initial concentrations of each were 200 ppm. During the degradation of the dyes, electrochemically generated chlorine and hypochlorite ions (OCl)– played pivotal roles. Under the aforementioned ideal circumstances, the minimum energy consumption values for bromothymol blue and methyl red were 0.2025 and 0.0636 kW h m–3, respectively. The anode exhibited an excellent service life for treating dye wastewater, and repeated tests and surface analysis revealed no evident passivation. In this way, a variety of dyes in effluents can be cheaply degraded by electrolyzing with a Ti/Ru0.3Ti0.7O2 anode, utilizing readily available electrolytes and with minimal electricity requirements.
... 18 Hydroxyl radicals (OH°), which are produced at the anode during the EO process, totally and unselectively mineralize organic contaminants (toxic and bio-refractory) to water, CO 2 , and other final by-products. 19 Recently, several studies have concentrated on treating landfill leachate using electrochemical oxidation processes. 4,[20][21][22] Direct or indirect oxidation mechanisms are used on the anode to remove organics from wastewater using electrochemical oxidation processes. ...
In this study, Pd and Co metal oxides, electrochemically deposited on a titanium (Ti) substrate, were utilized to remove chemical oxygen demand (COD), NH3-N, and turbidity from diluted Bingöl leachate. The plating bath was prepared with 7 mM palladium chloride (PdCl2) and 1 mM cobalt chloride (CoCl2), along with 1.68 M NH4Cl, and 0.16 M H3BO3. In the electrooxidation (EO) cell, the anode consisted of a Ti/PdO-CoO electrode, while the cathode was a stainless-steel electrode. The Ti/PdO-CoO electrode demonstrated an actual functional life of 96 h, as determined through accelerated life testing. X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy examinations revealed that the surface of the Ti substrate was coated with PdO and CoO. Turbidity, NH3-N, and COD were electrooxidized indirectly due to the high chloride content (718 mg l⁻¹). In the presence of 10 mM NaCl, the highest removal efficiency for NH3-N, COD, and turbidity was 60.5%, 64.9%, and 96.5%, respectively. The removal of COD, NH3-N, and turbidity fit pseudo-second-order (PFO) kinetics (R² 0.97–0.99). For a COD efficiency of 60.5% at 25 mA cm⁻², the corresponding energy consumption, unit energy consumption, and electrode cost were 56.25 kWh m⁻³, 200.89 kWh/kg-COD, and 2.37 ($/kg-COD), respectively.
... The EAOPs operate on the principle of generating reactive oxygen species (ROS) in situ through the utilization of electrons as a clean reagent. Electrochemical oxidation (ECO) is the simplest EAOP and employs an electrode (M) with high overpotential for oxygen evolution (e. g., boron-doped diamond (BDD), PbO 2 , and SnO 2 ) as anode to produce hydroxyl radicals M( • OH) according to Eq. (1) [23][24][25][26][27]. This heterogeneous process is controlled by mass transfer since the pollutant should reach the electrode surface where the electrogenerated • OH remains physisorbed on the anode surface [28][29][30]. ...
... Within this context, the advanced oxidation processes (AOPs) become a viable solution [3], wherein electrochemical AOPs (i.e., EAOPs) notably excel due to their efficiency and environmental compatibility [4]. EAOPs stand out for their ability to generate hydroxyl radicals ( • OH), which effectively break down structurally complex contaminants into less harmful molecules [5]. In electro-oxidation (EO), a subset of EAOPs, an anode is employed to facilitate the production of these powerful oxidizing agents. ...
The depletion of clean water resources and the consequent accumulation of contaminants in aquatic systems must be urgently addressed by means of innovative solutions. Electro-oxidation (EO) is considered a promising technology, prized for its versatility and eco-friendliness. However, the excessively high prices and the toxicity associated with some of the materials currently employed for EO impede its broader application. This study introduces cost-effective Ni-Mn binary oxide anodes prepared on Ni foam (NF) substrate. A scalable synthesis route that enables a 35-fold increase in the production of active material through a single optimization step has been devised. The synthesized binary oxide material underwent electrochemical characterization, and its effectiveness was assessed in an electrochemical flow-through cell, benchmarked against single Ni or Mn oxides and more conventional alternatives like boron-doped diamond (BDD) and dimensionally-stable anode (DSA). The novel binary oxide anode demonstrated exceptional performance, achieving complete removal of phenol at very low current density of 5 mA cm−2, along with an 80% of chemical oxygen demand (COD) decay within only 60 min. The NF/NiMnO3 anode outperformed the BDD and DSA when using comparable projected surface areas, owing to its high porosity and ability to produce hydroxyl radicals, as confirmed from the degradation profiles in the presence of radical scavengers. Furthermore, GC/MS analysis served to elucidate the degradation pathways of phenol.
... In the direct method of electrolysis, direct electron exchange with pollutants occurs at the anodic surface, destabilizing or degrading the pollutants, whereas, in the indirect electrolysis method, electron exchange with pollutants is mediated by active species. In both types of electrolysis, the redox catalysis chain connects anodic surfaces to contaminants via a series of reversibly or irreversibly generated electroactive compounds [15]. Physically absorbed hydroxyl radicals (•OH) generated through non-active anodes also enhance the process efficiency by indirectly oxidizing the majority of organic molecules [16]. ...
The current study focused on the charge and mass transport effect on the continuous electro-Fenton (EF) process treatment of synthetic Reactive orange 16 (RO16) dye using low-cost stainless-steel electrodes and sodium chloride (NaCl) supporting electrolytes, respectively. Lab-scale experiments were carried out in a 500 mL volume reactor cell at various initial RO16 dye concentrations (75-250 mg/L) and flow rates (0.05-0.4 L/h). The results showed that the decolorization rate increased quantitatively with an increment of the RO16 dye concentration and flow rate due to the mass transport limitation. Increasing the mass flow rate increased the mass transfer coefficient (km), improving the kinetics of the decay. It was found that regardless of inflow concentrations, the dye removal efficiency increased with the flow rate. Additionally, the degradation rate, elimination capacity, current efficiency (CE), and specific energy requirement were estimated for the process. A dimensionless current density relation was generated for the developed continuous stirred tank to describe the kinetics and mass transfer relationship towards the overall reaction rate contribution. It was found that the stainless-steel anode electrode proved to be preferable due to lower energy consumption (6.5 kWh m-3) and less iron sludge production. Additionally, the application of pyrite (FeS2) particulate electrode increased the process efficiency (~ 5%) for TOC removal and current mineralization while maintaining its sustainability for reuse.
... Electrocatalysis entails the introduction of new material onto an anode surface to alter the electrochemical reaction rate, hence giving new reaction pathways under the same potential or electric field without hindering the electron transfer rate Majumdar et al., 2018). The electrocatalytic degradation of organic pollutants occurs through (a) direct transfer of electrons to the anodic surface; (b) water discharge at the anode that leads to the production of physisorbed • OH; (c) indirect oxidation by the electrochemically generated oxidants (e.g., Cl 2 , HOCl) on the anode (Martínez-Huitle and Panizza, 2018;Panizza, 2014;Särkkä et al., 2015;Shankar et al., 2009;Wenk et al., 2013) (Eqs. Table S2), (b) Electrocatalysis (Data source: Table S3), (c) Fenton-based processes (Data source: Table S4), (d) Sulfate radical-based AOPs (Data source: Table S5). ...
Micropollutants have become ubiquitous in aqueous environments due to the increased use of pharmaceuticals, personal care products, pesticides, and other compounds. In this review, the removal of micropollutants from aqueous matrices using various advanced oxidation processes (AOPs), such as photocatalysis, electrocatalysis, sulfate radical-based AOPs, ozonation, and Fenton-based processes has been comprehensively discussed. Most of the compounds were successfully degraded with an efficiency of more than 90%, resulting in the formation of transformation products (TPs). In this respect, degradation pathways with multiple mechanisms, including decarboxylation, hydroxylation, and halogenation, have been illustrated. Various techniques for the analysis of
micropollutants and their TPs have been discussed. Additionally, the ecotoxicity posed by these TPs was determined using the toxicity estimation software tool (T.E.S.T.). Finally, the performance and cost-effectiveness of the AOPs at the pilot scale have been reviewed. The current review will help in understanding the treatment efficacy of different AOPs, degradation pathways, and ecotoxicity of TPs so formed.
... 1 Most published studies on VOC removal have used conventional electrochemical cells with the electrodes immersed in a liquid electrolyte solution. [2][3][4] However, it is well known that the solubility of most VOCs in aqueous medium is highly limited. 5,6 Many studies have used electrocatalytic reduction 7,8 or electrocatalytic oxidation 9,10 for VOC removal even though these are mass transfer limiting processes. ...
Electrochemical methods have been widely used to remove gaseous pollutants that are dissolved in liquids. However, there have been no significant attempts made to remove gaseous pollutants in their gas state, especially through electrochemical method. We attempted to remove gaseous acetaldehyde (AA) through electro-oxidation using an Ag-Hg bimetallic catalyst coated on a Ni foam electrode at a gas–solid interface. The interface was induced by a semi-solid agar gel in a membrane-divided electrolytic cell. We found that the semi-solid gel was a suitable solid electrolyte. Under inlet conditions of 15 ppm with a flow rate of 200 mL min-1, we could achieve up to 80% AA degradation. This was due to the effective transfer of electrons in the presence of the semi-solid gel, which was eight times higher than that obtained in the zero-gap method. In continuous operation of the electrochemical reactor with a single-pass of AA, we consistently achieved a removal capacity of 169.81 mg cm-2 hr-1 over a 1-h period in an Ar atmosphere. These results demonstrate the practical applicability of this electrochemical system developed using a liquid-free electrolyte and a bimetallic catalyst for the electrode.
... The cathodic process takes place at the cathode, where hydrogen peroxide (H 2 O 2 ) is produced through the iron catalyst on the electrode surface, which is constantly renewed. Oxygen or air is continuously delivered to the area around the cathode to produce H 2 O 2 [77]. This procedure is called electro-Fenton reaction (EF). ...
Huge amounts of noxious chemicals from coal and petrochemical refineries and pharmaceutical industries are released into water bodies. These chemicals are highly toxic and cause adverse effects on both aquatic and terrestrial life. The removal of hazardous contaminants from industrial effluents is expensive and environmentally driven. The majority of the technologies applied nowadays for the removal of phenols and other contaminants are based on physio-chemical processes such as solvent extraction, chemical precipitation, and adsorption. The removal efficiency of toxic chemicals, especially phenols, is low with these technologies when the concentrations are very low. Furthermore, the major drawbacks of these technologies are the high operation costs and inadequate selectivity. To overcome these limitations, researchers are applying biological and membrane technologies together, which are gaining more attention because of their ease of use, high selectivity, and effectiveness. In the present review, the microbial degradation of phenolics in combination with intensified membrane bioreactors (MBRs) has been discussed. Important factors, including the origin and mode of phenols’ biodegradation as well as the characteristics of the membrane bioreactors for the optimal removal of phenolic contaminants from industrial effluents are considered. The modifications of MBRs for the removal of phenols from various wastewater sources have also been addressed in this review article. The economic analysis on the cost and benefits of MBR technology compared with conventional wastewater treatments is discussed extensively.
... The oxidation of organic matter during EO is divided in two different regimes: In the kinetic controlled regime, the applied current is below the limiting current. The rate constant is theoretically independent from COD concentration and the COD decreases linearly at maximum instantaneous current efficiency (ICE) of 100% (Panizza and Cerisola, 2009). During mass transfer limitation, the oxidation rate strongly depends on the COD concentration as diffusion governs the transport of organics towards the anode. ...
Boron-doped diamond (BDD) is considered as a high-performance electrode material for electrochemical oxidation (EO) of organic compounds or pathogens in wastewater. With its excellent physical, chemical properties and wide potential window, BDD surpasses the capabilities of classical electrodes. The present chapter provides an overview on the general issues of using BDD electrodes for such applications. It starts with a small discussion on different types BDD electrodes and their preparation methods. The main factors that affect the performance of BDD electrode have been discussed and evaluated. Then, we focus on the degradation mechanisms and reactor design that based on EO. More attention is paid to recent applications of electrochemical oxidation using BDD electrodes in various organic water treatment and disinfection. Finally, the prospective and challenge of BDD electrode in the upcoming future are discussed according to the existing problems in water treatment.
The degradation by biological processes of a large majority of organic volatile contaminants in wastewater is limited. This is so, largely because the reaction is inhibited at concentrations higher than 50 mg.L−1, thus, requiring costly physical or physiochemical pre-treatment(s). Electrochemistry currently plays an important role in a vast number of fundamental studies and applied areas in the treatment of pharmaceutical effluents. Pharmaceutical effluents are wastewater generated through various pharmaceutical processes such as the manufacturing of active pharmaceutical ingredients and product formulation. This wastewater is characterized by high concentrations of organic matter, catalysts such as TiO2/g-C3N4 and cathodic WO3/W nanocatalysts, and toxic pollutants that include Benzene, ethylbenzene, and Toluene). In recent times, electrochemical treatment has been attracting researchers as an emerging technology used for the removal of organic and inorganic impurities from water and wastewater. Many scientists are attempting to use these methods for the treatment of wastewater owing to the many advantages associated with electrochemistry compared to their biological or biotechnological counterparts. Although several review papers are available regarding the application of electrochemical methods for the environmental clean-up of pharmaceutical wastewater, research focussing on the development of efficient technologies coupled with the use of electrochemical and photocatalytic nanocatalysts continues. This chapter presents a detailed review of methods for the electrochemical degradation of volatile organic compounds in wastewater catalysed by nanocatalysts with an emphasis on pharmaceutical wastewater or effluents. An extensive review of the mechanism and application of these nanocatalysts-promoted electrochemical processes for degradation, mineralization, and detoxification of different organic pollutants present in industrial pharmaceutical wastewater will be reported. Electrochemical methods for the destruction of organic pollutants in wastewater is becoming very attractive in the industry because it is a powerful and promising clean method with undisputable environmental friendliness. Furthermore, the electrochemical treatment methods can be set up easily and show high efficiency. Analytical challenges encountered in the physical and electrochemical characterisation of some of these nanocatalysts will be briefly discussed. The reason for an accurate analytical characterisation is to check the composition, structure, dispersion on, and active surface area of the nanocatalysts, as well as the electrochemical systems. This guarantees the quality of the electrochemical data obtained. Finally, electrochemical and differential electrochemical mass spectrometry measurements used in specific cases to study and evaluate the influence of the electrocatalyst structure on its electroactivity will be discussed. This type of study allows for the investigation of the effect of the composition in terms of foreign metal atoms and atomic content of nano-metals-based catalysts (e.g. ZnO, TiO2, or CuO) towards the electro-oxidation of the organic pollutants. This chapter concludes by presenting the summary of the principles, advantages, and limitations, as well as the performances and some of the successful applications of the nanocatalysed electrochemical degradation of volatile organic compounds in wastewater using pharmaceutical effluents as an example.
Electrocatalysis is a pivotal scientific discipline and a crucial part of industrial processes for the sustainable future for mankind. It is closely related to energy efficiency and the general processing rate of various electrochemical applications. Thus, a sound understanding of electrocatalysis provides versatile new functions and innovative solutions to numerous challenges we face in conventional and advanced technologies. Particularly, the challenges regarding the need for sustainable energy and water use arise with growing demands for more environmentally friendly, safer, and energy-efficient materials, which are less dependent on limited resources. In terms of resolving these challenging demands, the emergence of nanomaterials has brought a significant advance in technologies and enabled an in-depth and comprehensive understanding of electrocatalysis. In this book chapter, we explore various electrochemical applications of both conventional and advanced technologies by categorizing them into five functioning groups: harvest, removal, consumption, storage, and analytics. For these applications with a particular aspect of sustainable energy and water, we discuss the roles and fundamentals of electrocatalysis, including technical parts such as cell configuration and its core elements, as well as the theories of thermodynamics and kinetics. Furthermore, we discuss how nanomaterials development and research activities have contributed to the deep understanding of nanoelectrocatalysis by reviewing some of the recent progress of various technologies. Finally, we explore the roles and the trend of these advanced nanomaterials in electrocatalysis with a focus on the properties and the design of materials.
In this study, the removal of moxifloxacin, an antibiotic of the fluoroquinolone group, from aqueous solutions was investigated using the electro-Fenton process. As the efficiency of the electro-Fenton process is highly dependent on the amount of H2O2 produced during process, the formation of H2O2 under acidic conditions was also investigated. In this context, the effects of applied current, cathode type and O2 flow rate on H2O2 production were investigated using boron-doped diamond anode. The highest H2O2 production was achieved using the boron-doped diamond anode and the graphite felt cathode. In addition, the optimum conditions for the applied current and oxygen flow rate for H2O2 production were determined to be 0.25 A and 0.1 L min−1, respectively. The effects of applied current and Fe2+ concentration in the electro-Fenton process on the removal of moxifloxacin were investigated. It was found that the moxifloxacin removal rate increased with increasing applied current. The highest H2O2 accumulation was observed at 0.25 A applied current, and moxifloxacin removal also reached 93.6% after 60 min. The moxifloxacin removal rate reached the highest value at Fe2+ concentration of 0.01 mM. This study provides promising results for the efficient treatment of moxifloxacin-containing wastewater by the electro-Fenton process without the addition of H2O2 using boron-doped diamond anode anode and graphite felt cathode.
Looking at modern approaches to catalysis, this volume reviews the extensive literature published on this area. Chapter highlights include Fenton chemistry, advanced manufacturing in heterogeneous catalysis, membrane reactors for light alkane dehydrogenation, and new insights and enhancement of biocatalysts for biomass conversion in the bioproducts industry.
Appealing to researchers in academia and industry, the detailed chapters bridge the gap from academic studies in the laboratory to practical applications in industry, not only for the catalysis field, but also for environmental protection. The book will be of great benefit to any researcher wanting a succinct reference on developments in this area now and looking to the future.
In the world’s rapidly expanding economy, textile industries are recognized as a substantial contributor to economic growth, but they are one of the most significant polluting industrial sectors. Dye-contaminated water sources can pose serious public health concerns, including toxicity, mutagenicity, and carcinogenicity among other adverse health effects. Despite a limited understanding of efficacious decolorization methodologies, the pursuit of a sustainable strategy for the treatment of a wide spectrum of dyes remains a formidable challenge. This article conducted an exhaustive review of extant literature pertaining to diverse physical, chemical, biological, and hybrid processes with the aim of ascertaining their efficacy. It also elucidates the advantages and disadvantages, cost considerations, as well as scalability impediments of the treatment methodologies, thereby facilitating the identification of optimal strategies for establishing techno-economically efficient processes in the sustainable handling of these effluents. The hybrid configuration exhibited superior efficiency and was documented to surmount the limitations and constraints inherent to individual techniques. The study also revealed that most of the proven and established dye removal techniques share a common limitation viz., the generation of secondary pollution (i.e., sludge generation, toxic intermediates, etc.) to the ecosystem.
Nowadays, toxic/persistent organic micropollutants generated from different human activities contaminate natural water streams since conventional water and wastewater treatment plants remain inefficient to eliminate these pollutants. Alternatively, advanced oxidation processes (AOPs) constitute an efficient and environment friendly techniques to remove these pollutants from water and wastewater effluents. These processes are based on in situ generation of strong oxidants, like hydroxyl radicals, that are able to oxidize organic pollutants up to their mineralization. The Fenton process, which is based on the Fenton’s reagent (a mixture of hydrogen peroxide and ferrous iron), is one of the first AOPs. To enhance the efficiency of the Fenton process, several improvements have been achieved in recent years. This chapter focuses on the fundamental characteristics of this process and overviews Fenton-based processes such as photo-Fenton, electro-Fenton, and related processes as well as anodic Fenton and Fered-Fenton processes, including their application to the treatment of contaminated waters.
The intensive production of the organochlorine pesticide lindane (γ-hexachlorocyclohexane) caused vast amounts of HCH isomers’ residues during the past century’s second half. These residues were usually deposited or discharged in uncontrolled landfills close to the factories, generating soil and groundwater contamination hot spots. Large lindane-contaminated sites have been categorized in Europe, Asia, Africa, and Asia. The legacy of lindane production caused a substantial environmental problem that has not been solved yet. Solid and liquid residues generated as lindane wastes have caused contamination of topsoil and groundwater, and the remediation treatments applied should consider the type and location of this contamination. Two of these sites are located at Sabiñánigo (Spain), where two landfills, Sardas and Bailín, were contaminated with HCH-wastes by INQUINOSA, a lindane factory operating from 1975 to 1988. This chapter reviews some “on-site” and “in situ” chemical technologies recently proposed to remediate this site.
Electrooxidation as an alternative decentralized wastewater treatment technique has been considerably investigated to develop different remediation and disinfection solutions of diverse classes of wastewater and soil washing effluents. It is a clean technology with distinguished advantages such as high versatility, amenability, limited chemical addition and ease of operation at ambient temperature and pressure. This technology is highly efficient, and it has been established as a powerful decontamination technique for depolluting different classes of contaminated wastewater and soil washing effluents. In this chapter, the prospects, and challenges of electrooxidation and related processes applied to wastewater and contaminated soil treatment were summarized. The recent advances in anode materials applied in electrooxidation, the different anode designs and configurations were examined. Principles and mechanisms of electrooxidation coupled with other processes such as UV, ultrasonic irradiation and sulfate radical-based AOPs to accelerate and enhance pollutants mineralization, their advantages and limitations over electrooxidation alone were enumerated. Applications of electrooxidation and related processes as decentralize and point-of-use clean water technology, electrochemical disinfection and soil washing/flushing effluents treatment were discussed. The challenges and limitations of electrooxidation and related processes critically reviewed.
Anodic oxidation is a promising method for removing organic pollutants from water due to its high nonselectivity and effectiveness. Nevertheless, its widespread application is limited due to its low current efficiency, high energy consumption and low treatment rates. These problems may be overcome by the optimization of the process parameters, reactor design and electrode geometry, by coupling the experimental investigations with mathematical modeling. Here we review the modeling of anodic oxidation with focus on basics of this process, the competition phenomenon in real wastewater, flow cells and batch cells, historical aspects, general modeling equations, modeling with plate electrodes, modeling with porous 3-dimension electrodes and the density functional theory. Mathematical modeling can provide current, voltage and concentration distributions in the system. Mathematical modeling can also determine the effects on the performance of parameters such as diffusion layer thickness, flow velocity, applied current density, solution treatment time, initial concentration and diffusion coefficients of organic pollutants, electrode surface area, and oxidation reaction rate constant. Mathematical models allow to determine whether the limiting factor of the process is kinetics or diffusion, and to study the impact of competition of phenomena. The density functional theory provides information on probable reaction pathways and by-products.
The practical application of electrochemical oxidation technology for the removal of surfactants from greywater was evaluated using sodium dodecyl sulfate (SDS) as a model surfactant. Careful selection of electrocatalysts and optimization of operational parameters demonstrated effective SDS removal in treating a complex greywater matrix with energy consumption below 1 kWh g − 1 COD (Chemical Oxygen Demand), paving the way for a more sustainable approach to achieving surfactant removal in greywater treatment when aiming for decentralized water reuse. Chromatographic techniques identified carboxylic acids as key byproducts prior to complete mineralization. These innovative approaches represent a novel pathway for harnessing electrochemical technologies within decentralized compact devices, offering a promising avenue for further advancements in this field.
Written for environmental specialists and electrochemists, this advanced-level book describes the theory and practical application of electrochemical and photoelectrochemical methods for pollution detection, quantification and abatement. (REVIEW EN ENVIRONMENTAL SCIENCE AND TECHNOLOGY)
ENVIRONMENTAL ELECTROCHEMISTRY
Contents
Preface
Chapter 1. The Green Revolution
Chapter 2. Electrochemistry and Photoelectrochemistry: Fundamentals
Chapter 3. Electrochemistry of Pollutant Species
Chapter 4. Electrochemistry as Applied to Pollutant Sensing
Chapter 5. Electrochemical Remediation and Recycling
Chapter 6. Photoelectrochemical and Photocatalytic Approaches to Pollutant
Removal
Chapter 7. Electrochemical and Photoelectrochemical Disinfection of Water
Chapter 8. Commercial Perspective
Appendix A-D.
The electrochemical oxidation of an industrial wastewater containing aromatic sulphonated acids on a boron-doped diamond electrode (BDD) was studied using cyclic voltammetry and bulk electrolysis. The influence of the current density and flow-rate was investigated in order to find the optimum conditions. It was found that a polymeric film, which caused BDD deactivation, was formed in the potential region of water stability during oxidation, however it was removed by high-potential anodic polarisation in the region of O<sub align="right"> 2 </sub> evolution. The complete mineralisation of the wastewater was achieved over the whole range of experimental conditions examined, due to the production of hydroxyl radicals on the diamond surface. The oxidation of the aromatic sulphonated acids was favoured by a low current density and a high flow-rate meaning that the oxidation was a diffusion-controlled process.
Organophosphoric pesticides are widely used for crop and fruit tree treatment, but their disposal causes serious environmental problems. Two commercial organophosphoric pesticides (Monocrotophos and Phosphamidon) were treated by an electrolysis system using Ti/Pt as anode and stainless steel 304 as cathode. A number of experiments were run in a laboratory scale pilot plant and the results are presented. For Monocrotophos, the achieved reduction was over 28%, while for Phosphamidon it was nearly 26%. Phosphamidon had a higher energy demand than Monocrotophos. The COD/BOD5 ratio was improved considerably after electrolysis for both pesticides examined. Therefore, electrochemical oxidation could be used as a pretreatment method for their detoxification.
Because of its extraordinary chemical stability, diamond is a perspective electrode material to be used in electrochemistry and electrochemical engineering. In this review-article, the results of basic studies in the synthetic-diamond electrochemistry are summarized: the electrochemical kinetics, photoelectrochemistry, electrochemical impedance spectroscopy. Relations between the semiconductor nature and crystal structure of diamond and its electrochemical behavior are revealed. Prospects for using diamond electrodes in the electroanalysis, electrosynthesis, and environmentally-oriented industry are outlined.
Simple indoles undergo electrolytic degradation at potentials near +1 V vs the normal hydrogen electrode at a Pb/PbO2 anode. Oxidation is first order in both current and indole concentration. The reaction is characterized by low CO2 yields and high TOC values, that is, most of the carbon of the starting material remained in the solution after electrolysis. Monomeric, isolable oxidation products were not found even at high conversion. These results are consistent with the intermediacy of hydroxyl radicals, which are produced at the surface of the Pb/PbO2 anode by electrolysis of water, initiating the polymerization of the starting materials to water soluble products with high net current efficiency.
. The electrochemical oxidation of dilute aqueous solutions of pentachlorophenol (PCP) using Ti/SnO2 as an electrocatalytic material has been investigated. The studies were carried out in a two-compartment electrochemical
cell at three different current density values (10, 30 and 50 mA cm–2) at 25 °C and using 20 mg L–1 of PCP in 0.1 M NaOH (pH 10) as supporting electrolyte. The PCP concentration and the by-products of the oxidized solution
were monitored during the oxidation process using UV and HPLC techniques. For the three current densities investigated it
was found that the rate of PCP elimination depends only on the specific electrical charge. Likewise, the oxidation mechanism
was proved to occur through the participation of adsorbed hydroxyl radicals (·OH) formed on the SnO2 surface, whatever the current density used. However, as the applied current density was increased, a current efficiency lower
than 2% was obtained, which is due to mass transfer limitations. In addition, it was observed that the PCP was mineralized
to CO2 with conversion percentages as high as 92% and at current density values as low as 10 mA cm–2. The PCP degradation produces two other by-products of oxidation (
The electrochem. behavior of PbO2 and synthetic B-doped diamond thin film electrodes (BDDs) was studied in acid media contg. 4-chlorophenol (4-CP) by bulk electrolysis under different exptl. conditions. To quantify the electrochem. activity of a given electrode, for the electrochem. oxidn. of org. compds. (4-CP), the current efficiency of the anodic oxidn. was normalized taking into consideration mass-transport limitations. The normalized current efficiency (j) was defined as the ratio between the current efficiency of the investigated anode to the current efficiency of an ideal anode which has a very fast oxidn. rate, resulting in a complete combustion of orgs. to CO2. The results showed that even if the complete combustion of 4-CP was achieved at both PbO2 and BDD anodes, the latter give higher j. The difference in reactivity of the electrogenerated hydroxyl radicals on the anode surface, is proposed to explain the high j values obtained using B-doped diamond anodes. [on SciFinder (R)]
The treatment of textile wastewater, containing a high concentration of Cl- ion, by an electrochemical method using Ti/RuO2, Ti/Pt and Ti/Pt/Ir electrodes is investigated. All three anodes proved to be very effective in direct or indirect oxidation of organics present in the wastewater.
After 60 min of electrolysis at 6 A/dm2, COD was reduced by 85-92% and DOC by about 85%. Of the three electrodes tested, the efficiency of organics removal followed the order: Ti/RuO2 > Ti/Pt > Ti/Pt/Ir. The electrochemical treatment of textile wastewater resulted in the production of many chloroorganics in high concentration. GC-MS analysis showed the presence of the following major products: 1,1-dichlorocyclopentene, 2,3-dichloro-2-methylbutane, chloromethylsilane, 2,3-dichloro-2-methyl butanoic acid, 2,3-dichloro-2-methyl propanol, 2,3-dimethyl-2, 3-butanediol and 2-butylphenol.
The electrical properties of tin oxide films have been measured as a function of phosphorus doping. It is shown that the electron concentration increases monotonically with phosphorus doping, with about 7.7% of the incorporated phosphorus being active. An oxygen deficiency is also present in these films, and is found to be about 0.1 eV below the conduction bandedge. The mobility increases with phosphorus doping to a maximum of 26 cm²/V sec, and then falls off with further doping, as the film undergoes a crystalline to amorphous transition. Film behavior in these two regimes can be explained by the established theories for current transport in polycrystalline and amorphous films, respectively.
The destruction of hazardous organic waste produced as waste products in chemical processes has become an industry in itself regulated by environmental agencies and government bodies. The environmentally harmful waste has been incinerated at high temperature with the aim of forming less harmful and less complex compounds, but this may lead to dioxin formation in the presence of chlorine-containing waste. It may also be treated electrochemically to result in carbon dioxide and water: One on-site electrochemical method, described here, which uses platinum-plated titanium electrodes, can treat most organic waste materials very effectively at low temperatures.
This article describes a novel electrochemical process, developed by AEA Technology at their Dounreay site, for the safe destruction of a wide variety of organic waste types. The new process involves the electrolytic production of highly oxidising species in an electrolyte consisting of a silver salt, usually silver nitrate, in nitric acid. These oxidising species in turn attack the organic waste material, ultimately converting it to carbon dioxide, carbon monoxide and water, along with inorganic compounds arising from any hetero-atoms, such as phosphorus or sulphur, which are converted to phosphate and sulphate, respectively. This process is made possible by the unique characteristics of the platinum group metals as electrode materials. At the heart of the system is an electrochemical cell, consisting of an anode compartment, a cathode compartment and a membrane separator.
Electrochemical techniques have considerably widened their scope over the past few years and industrial chemistry has developed rapidly, as has the availability of a wide spectrum of reactor geometries for diverse applications. The contributions that electrochemical technology is making to environmental protection and the avoidance of pollution are discussed. Some applications which have reached pilot- or full-scale developments are described. These include metal ion removal, destruction of dissolved organics, flue gas desulphurization, and electrochemical synthesis. Requirements for the further expansion of the number of application areas and the scale of operation for environmental electrochemistry are discussed.
This paper deals with the study of the performance of lead dioxide anodes for phenol degradation in aqueous solution. The lead dioxide is prepared in the laboratory either by positively polarizing a metallic lead support in siilfitric acid solution or by electrodeposilion on a substrate using a lead nitrate electrolyte. Electrolyses of acidic solutions of phenol (pH=2) at an initial concentration of 21 mmole dm-3 are performed at an anode current density of 1000 Am-2 and at T=70°C. The main products are 1, 4-benzoquinone, maleic acid and carbon dioxide. The kinetics of the phenol degradation is followed by HPLC and TOC analysis. The presence of sodium dodecyl sulfate, acetate ions and Cu2+ in the electrolytic solution of the PbO2 preparation decreases its efficiency and its resistance to corrosion. It is generally accepted that these species, which can be incorporated into the PbO2 deposit, modify its electrocatalytic properties. This study has also shown the effect of the type of substrate (Pb, Ti/(IrO2-Ta2O5) and Ta) on the stability and efficiency of PbO2 deposits for phenol degradation. The efficiency of the laboratory prepared electrodes decreases according to the type of substrate used as follows : Ta > Ti/(IrO2-Ta2O5) > Pb. Longevity tests have shown that the electmde Ti/(IrO2-Ta2O5)/PbO2 is much less efficient after 20 hours of use, while Ta/PbO2 has the same performance after 160 hours of operation.
Ultrathin films (ca. ≤0.5 μm) of lead oxide, concluded to be PbO, were generated on the surfaces of Au, Pt, Ti, and GC electrodes during rapid voltammetric dissolution of thick films (> ca. 10-100 μm) of β-PbO2 deposited from acidic solutions containing Pb2+. These PbO films were stable at potential values > ca. 0.5V negative of the peak potential for cathodic stripping of bulk PbO2. Ultrathin films of PbO2 were produced, in turn, by anodization of the PbO films in Pb2+-free solutions. Results are emphasized here for the voltammetric and microscopic characterization of these thin films at Au electrodes. The formation of the stable PbO film during cathodic dissolution of thick PbO2 films is concluded to be the result of a deficiency of H+ in the interfacial region between the substrates and the porous thick oxide films. Ultrathin PbO films were oxidized to ultrathin PbO2 films during a positive potential scan and were determined to be electrocatalytically active for oxidation of dimethylsulfoxide (DMSO) at E > 1.5V vs. SCE when Bi3+ was present in the test solutions.
Anodic electrodes for ozone generation were prepared with lead dioxide particles of various diameters. The lead dioxide particles were characterized with X-ray diffraction analysis, and the electrodes were characterized and performed for ozone generation. It was revealed that both the diameters of the lead dioxide particles and the contents of the pore forming agent have great effect on the performance of the electrodes. With decreasing of the diameters of the lead dioxide particles from the range of 55-74 urn to the range of 15-35 μm, the performance of the electrodes improved. But no further improvement was found with further decreasing of the particle diameters to the range of 5-15 μm. However, by employing an appropriate amount of pore forming agent during the electrode preparations, the performance of the anodic electrode can be improved. The optimized weight ratio of ammonium oxalate to lead dioxide is 1.33/100.
Difference voltammetry at rotated disk electrodes was applied to a study of several anodic O-transfer reactions that appear to occur concurrently with O2 evolution. This voltammetric technique was useful for extracting the rotation-dependent component of the total current from the large, virtually rotation-independent current for O2 evolution. Data for oxidation of I- at Pt, Au, Pd, Ir, and glassy carbon electrodes show that the E1/2 for IO3- production is correlated with the overpotential for O2 evolution at these electrode materials. Data obtained at an Ir electrode for various reactions with widely varying E° values reveal uniform E1/2 values closely correlated with the potential for onset of O2 evolution in both alkaline and acidic solutions. The results support the conclusion that the anodic discharge of H2O is a prerequisite of these anodic O-transfer mechanisms.
Highly boron-doped diamond (BDD) electrode was used as anode for ozone generation system by electrolysis of acidic solution. We have succeeded to generate ozone by using this BDD electrode with high efficiency compared to traditional lead oxide (PbO 2) electrode. Ozone generation by using PbO 2 electrode was gradually decreased due to its structural degradation at continous operating. However, electrochemical and physical properties of the BDD electrode were kept its high stability even after long operation time (>3000 hours) in comparison with PbO 2 electrode. The stability of BDD electrode for long time operation was due to physical and chemical properties of diamond electrode. It was expected that the use of BDD electrode as an anode would make a positive contribution to the electrochemical ozone generation.
The formation of O2/O3 on PbO2 from the electrolysis of water in neutral solutions is shown here to present some analogies and some differences with respect to the same process in acid media. The electrolyte composition affects the current efficiency for O3 formation (n) and the cell potential (E) of a Membrel type electrochemical assembly. An improvement in n and a decrease in E is observed upon addition of relatively low amounts of Na2SO4 or NaClO4 in pure water. We observe no effect of NaNO3 on either parameters. In agreement with literature data in acid solutions, F- causes an increase in both n and E. The results of electrochemical kinetic investigations with electrodes of PbO2 electrodeposited on Ti confirm the above data. Current-potential curves constructed from measurements in NaNO3 show a region of Tafel linearity with slopes of 2RT/F and RT/F in the low and high currents range, respectively. Addition of Na2SO4 and NaClO4 to NaNO3 has an effect on the process at more positive potentials only: the RT/F slope decreases toward a value of RT/2F as the concentration of the "foreign" salt is increased. As an explanation of the observed behaviour, the possibility is advanced that a step following the discharge of water is rate determining at high positive potentials with the adsorption of intermediates described by Temkin conditions. The composition of the electrolyte is expected to influence the yield of ozone formation by affecting the coverage and free energy of adsorbed oxygen intermediates.
Wastewater treatment technology is undergoing a profound transformation due to far-reaching changes in regulations governing the discharge and disposal of hazardous pollutants. Electrochemistry for the Environment first lays down the fundamentals of environmental electrochemistry, introducing the basic techniques in selecting electrode materials and fabricating them, followed by the theoretical analysis of the electrochemical processes and the green electrochemical operation. Then it discusses the electrochemical technologies in water/wastewater treatment using BDD before moving on to an examination of the established wastewater treatment technologies such as electro-coagulation, -flotation, and-oxidation. Additionally, emerging technologies such as electrophotooxidation, electrodisinfection, and electrochemical technologies in sludge and soil treatment are analyzed. This book is an excellent reference for electrochemists, chemical engineers, environmental engineers, civil engineers, and also for those in industry evaluating and implementing new technologies. © Springer Science+Business Media, LLC 2010 All rights reserved.
Methodology for the electrochemical decomposition of bisphenol A is described. The electrochemical behaviour of bisphenol A at a Pt electrode was investigated by means of cyclic voltammetric techniques. The electrochemical oxidation of bisphenol A led to the deactivation of the electrode as a result of the deposition of an electropolymerized film. However the electrochemical decomposition of bisphenol A could be achieved by the use of a platinum coated titanium (Pt/Ti) electrode and a tin dioxide coated (SnO2/Ti) electrode. The electrolysis was carried out galvanostatically at a constant current of 0.3 A. The mineralization of bisphenol A was monitored by determining the amount of total organic carbon. Furthermore, the generation and nature of intermediates produced in the electrochemical reactions was investigated. Although large amounts of aliphatic acids were generated by electrolysis with the Pt/Ti anode, they were produced only to a small extent in at the SnO2/Ti anode. In the case of the SnO2/Ti anode, bisphenol A is rapidly oxidized to carbon dioxide and water, compared to the Pt/Ti anode.
The electrochemical oxidation of oxalic acid (OA) has been studied, in acidic media, at Ti/PbO2, highly boron-doped diamond (BDD), Pt, Au and Ti/IrO2–Ta2O5 electrodes, by both cyclic voltammetry and bulk electrolysis. The anodic oxidation of OA has clearly shown that the electrode material is an important parameter when optimizing such processes, since the mechanism and the products of several anodic reactions are known to depend on the anode material. OA was oxidized at several substrates to CO2 with different results; however, higher current efficiencies were obtained at Ti/PbO2, Pt and BDD. At Ti/PbO2, the carboxylic groups are expected to strongly interact with the Pb(IV) sites and the hydroxyl radical formed on/at the electrode surface. In some cases, complex interactions exist between the organic substrate and the electrode surface, as confirmed by the oxidative behavior of OA at the Pt electrode.
This report summarizes results obtained as part of a larger effort to demonstrate the applicability of electrolytic procedures for the direct anodic (oxidative) degradation of toxic organic wastes. The authors refer to this process as electrochemical incineration (ECI) because the ultimate degradation products are equivalent to those achieved by thermal incineration processes. In this work, the ECI of 4-chlorophenol is achieved in an aqueous medium using a platinum anode coated with a quaternary metal oxide film containing Ti, Ru, Sn, and Sb oxides. The electrode is stable and active when used with a solid Nafion membrane without the addition of soluble supporting electrolyte. Liquid chromatography (LC), including reverse phase and ion exchange chromatography, is coupled with electrospray mass spectrometry (ES-MS) and used, along with gas chromatography-mass spectrometry (GC-MS) and measurements of pH, chemical oxygen demand (COD), and total organic carbon (TOC), to study the reaction and identify the intermediate products from the ECI of 4-chlorophenol. Twenty-six intermediate products are identified and reported. The most abundant of these products are benzoquinone, 4-chlorocatechol, maleic acid, succinic acid, malonic acid, and the inorganic anions chloride, chlorate, and perchlorate. After 24 h of ECI, a solution that initially contained 108 ppm 4-chlorophenol yields only 1 ppm TOC with 98% of the original chlorine remaining in the specified inorganic forms. LC-ES-MS and direct infusion ES-MS detection limits are between 80 ppb and 4 ppm for these intermediate products. Elemental analysis of the electrolyzed solutions by inductively coupled plasma mass spectrometry ICP-MS showed that only trace amounts of the metallic elements comprising the metal oxide film were present in the solution.
Electrochemical oxidation has been proposed as a remediation method for chlorinated phenols but is hampered by anode fouling. In this work the authors explore the mechanism of anode fouling by chlorinated phenols, compare structure vs reactivity for phenols differing in the extent of chlorination, and relate the efficiency of oxidation to the mechanism of oxidation at different electrode types. Linear sweep voltammograms at a Pt anode at several concentrations, sweep rates, and pH were interpreted in terms of deposition of oligomers on the anode surface. Chronopotentiometry at Pt showed that the oxidation potentials of the chlorinated phenol congeners ranged from +0.6 to +1.3 V vs SHE in the pH range 2--12; four electrons are transferred for mono- and trichlorophenols and two for pentachlorophenol. Passivation increased in parallel with the uncompensated resistance of the solution and occurred only at potentials at which water is oxidized, suggesting that the formation of the oligomer film involves attack of hydroxyl radicals on electrochemically oxidized substrate. Seven chlorinated phenols were electrolyzed at PbO{sub 2}, SnO{sub 2}, and IrO{sub 2} anodes. Relative reactivities of congeners were anode-dependent, due to different mechanisms of oxidation: direct electron-transfer oxidation at PbO{sub 2} and hydroxyl radical attack at SnO{sub 2} and IrO{sub 2} At current densities <0.1 mA cm{sup {minus}2}, current efficiencies >50% could be achieved with 4-chlorophenol at all three anodes.
This article reviews electrochemical processes and devices that can contribute to a cleaner environment. Electrochemical processes for treatment of waste water solutions, flue gases and contaminated groundwater and soil are described, as well as improvements of existing electrochemical processes or products in order to minimize their environmental impact. Electrochemical power sources for cleaner generation of electricity in fuel cell power stations and for electrically driven vehicles are also discussed. Finally, the important role of electrochemical sensors for monitoring toxic substances is stressed.
Current efficiencies are compared for the generation of O[sub 3] simultaneously with O[sub 2] during anodic discharge of H[sub 2]O at pure and iron(III)-doped [beta]-lead dioxide film electrodes in phosphate buffer (pH 7.5, 10 C) containing 2.5 mM KF. Also examined is the effect of applied current density. A current efficiency of 14.6% was obtained for the Fe(III)-doped PbO[sub 2] film electrode deposited on a internally cooled (10 C) tubular titanium substrate at a current density of 200 mA cm[sup [minus]2] as compared to only 6.1% at the undoped PbO[sub 2] electrode under the same conditions. This result is tentatively explained on the basis of a mechanism involving the transfer of oxygen from hydroxyl radicals adsorbed on Pb(IV) sites adjacent to Fe(III) sites to O[sub 2] adsorbed at the Fe(III) sites in the surface of the Fe(III)-doped PbO[sub 2] electrodes.
Leachate originating in landfills where municipal solid wastes are disposed is a wastewater with a complex composition that could have a high environmental impact. The primary goal of this research was to investigate the feasibility of removing refractory organic pollutants and ammonium nitrogen from landfill leachate by electrochemical oxidation. The effects of current density, pH, and chloride concentration on the removal of both chemical oxygen demand (COD) and ammonium nitrogen were investigated. Titanium coated with lead dioxide (PbOâ) or tin dioxide (SnOâ) was used as the anode. An effective process was achieved in which the leachate was decolorized, COD was removed up to a value of 100 mg Lâ»Â¹, and ammonia was totally eliminated. Average current efficiency of about 30% was measured for a decrease of COD from 1200 to 150 mg Lâ»Â¹, while efficiency of about 10% was measured for a near complete removal of ammonium nitrogen, starting from an initial value of 380 mg Lâ»Â¹. Results indicated that the organic load was removed by both direct and indirect oxidation. Indirect oxidation by chlorine or hypochlorite originating from oxidation of chlorides is believed to be mainly responsible for the nitrogen removal.
The influence of an IrO2 interlayer between the Ti substrate and the SnO2–Sb2O5 coating on the electrode service life and on the efficiency of p-chlorophenol (p-CP) oxidation for wastewater treatment has been investigated. The results have shown that if the loading of the SnO2–Sb2O5 coating relative to the IrO2 interlayer loading (? ratio defined by Equation 1) is high (? = 20–30) the service life of the electrode can be increased without modification of the ability of this electrode to perform p-CP oxidation. This suggests that the oxidation of p-CP using a Ti/IrO2/SnO2–Sb2O5 electrode with high ? ratio (? > 20) occurs only through the SnO2–Sb2O5 component of the electrode, with no interference of the IrO2 interlayer. However, the electrode potential at a given current density is considerably lower in the case of the Ti/IrO2/SnO2–Sb2O5 electrode. In order to explain this decrease in electrode potential we speculate that water is firstly discharged on IrO2, which is present in small amounts on the surface, forming hydroxyl radicals at a relatively low potential. These active hydroxyl radicals then migrate (spill over) towards the SnO2–Sb2O5 coating, where they are physiosorbed and react with p-CP leading to complete combustion.
The service life of SnO2–Sb2O5 coated anodes prepared by the spray pyrolysis technique using Ti or Ti/IrO2 substrate, was studied under galvanostatic conditions (100mAcm–2 in 1m H2SO4 at 25°C. The results showed that the presence of an IrO2 interlayer between the Ti substrate and the SnO2–Sb2O5 coating (Ti/IrO2/SnO2–Sb2O5 anode) strongly increases the service life of the anode. This beneficial action of the IrO2 interlayer was attributed to its high anodic stability and its isomorphous structure with TiO2 and SnO2. Cyclic voltammetry and steady-state polarization curves showed that the electrochemical behaviour of the Ti/IrO2/SnO2–Sb2O5 electrode lies between the behaviour of the Ti/IrO2 and the Ti/SnO2–Sb2O5 electrodes due to incorporation of IrO2 in the SnO2–Sb2O5 coating during its preparation.
Tannery wastewater (real and synthetic) was treated by an electrochemical method with the principal aim of eliminating ammonium. Of various materials tested as electrodes graphite proved the best anode and steel the best cathode. Ammonium elimination was negatively influenced by the presence of organic pollutants and sulphides. The best results were obtained using electroxidation as a polishing step for the final effluents of a biological treatment plant. Ammonium elimination efficiency after 30 min of electrolysis at a current density of 0.44 A/dm was equal to 99%. For these conditions energy consumption for the elimination of 1 kg of NH4 was 132 kwh. The process was less efficient when applied to raw and partially treated wastewater: to achieve the same result, electroxidation time had to be doubled and current density to be increased about threefold. COD removal was satisfactory when the initial values were relatively low (less than 300 mg/l) and only partial (about 70%) while treating wastewater with initial COD above 1200 mg/l.In conclusion the process can be used as a polishing step for the final effluent from a biological treatment plant for tannery wastewater. In some extreme situations it can also replace biological nitrification.
Synthetic boron-doped diamond (BDD) thin film electrodes were tested for the electrogeneration of silver(II). In nitric acid, the kinetics of the silver(I)/silver(II) couple were studied by cyclic voltammetry. The results demonstrate that silver(II) can be produced with high current efficiency by silver(I) oxidn. at BDD electrodes. At low concn. of nitric acid and high concn. of silver(I), AgO is formed on the electrode surface. [on SciFinder (R)]
Anodic oxidation of phenol at a graphite electrode has shown good treatment efficiency. The removal efficiency was a function of the current applied, with around 70% phenol removal efficiency at a current of 2.2 A. After about 5 months of operation, there was no sign of deterioration of the graphite bed. An empirical relationship was developed relating phenol removal efficiency to the current. The relationship showed excellent prediction of the experimental data. Furthermore, a methodology for calculating the cell capacity was developed. The relation between the cell capacity and phenol residual concentration was modelled using a non linear model. Preliminary design procedure for the electrochemical cell was illustrated and the designs results for nine different wastewater conditions were tabulated. Economic evaluation of the process under different scenarios was presented and compared with other processes.
In denim production the decolourisation of intensively coloured, indigo-particulate containing waste water is a factor of major environmental concern. Successful anodic decolourisation of solutions containing 0.29 mM dispersed indigo and 0.070 M Na2SO4 could be achieved on boron-doped diamond electrodes. Current densities were varied from 0.36 to 80 mA cm−2. Relative current efficiency decreases with increased current density from 43% to less than 1% at 80 mA cm−2. At higher concentration of dispersed indigo of 25.1 mM, increased relative current efficiency is observed.Diffusion limited current density for decolourisation of 0.292 M indigo dispersion can be calculated with 0.166±0.007 mA cm−2. At the experimental conditions studied, peroxodisulfate, formed as by product of the electrolysis, was found to be ineffective for dyestuff destruction.Experiments in presence of small amounts of chloride proved, that the observed decolourisation of the dispersed indigo cannot be attributed to hypochlorite, formed by anodic oxidation of chloride. While anodic decolourisation of a soluble reactive dye proceeds rapidly, commercial vat dyes resist to oxidative anodic attack at the conditions chosen.Bleach experiments of dyed fabric failed, which supports the model of indigo oxidation in the diffusion layer of the anode.
Active carbon fiber was used as electrodes to treat several simulated dyeing wastewater and factual textile-dyeing wastewater from a textile-dyeing operation at Shanghai. This method was found to be quite effective and highly competitive in contrast with Fenton's reagent. Several operating variables, such as voltage, pH and salt added were studied to ascertain their respective effect on the treatment efficacy. According to the experiment, nearly all the wastewater's chromaticity removals were higher than 90%, with COD removals within ca. 40–80%.
Twelve different adsorbents, originating from waste materials, were used to treat an effluent, of complex composition, from a chemical works. The effectiveness of each adsorbent was measured in terms of its effect on the colour (absorbance at 450 nm) and COD levels of the effluent and also in terms of its adsorption capacity towards individual constituents of the effluent. The results showed that all adsorbents would physically adsorb constituents in reversible processes. Some constituents were more readily adsorbed than others. This meant that little correlation was observed between changes to the colour and COD levels of the effluent, because individual constituents made different contributions to these properties. The problem is further complicated by adsorbents, particularly those which had not been processed, contributing new constituents to the effluent. Thermodynamic data obtained from this study were used to predict the relative distribution of three constituents on the surface of different adsorbents. These results suggest that, for this effluent, adsorption onto waste material would be most effectively applied by using it in combination with other removal techniques.
Phenol degradation was carried out in acidic aqueous solution on different crystal structures of PbO2 surfaces at room temperature. Phenol, benzoquinone and maleic acid concentrations were monitored during the electrolysis process. It was determined that β surfaces have higher performance than α surfaces on phenol degradation. Then, the effect of crystallinities of pure β-PbO2 surfaces was investigated and found that higher crystallinity increased the efficiency of the phenol degradation process.
The design and optimization of large-scale systems for electrochemical dissolution of PuO2 in the presence of Ag2+ ions acting as mediators require a knowledge of true dissolution kinetics, usually obscured by limiting capacities of the electrolytic cells. Analysis conducted in this study identified the PuO2 surface reaction with silver(II) as the rate-controlling step and led to a mathematical model of the process based on first-order heterogeneous kinetics. By applying the model for simulation of a large-scale PuO2 dissolution experiment reported by Bourges et al., a first-order rate constant k=0.0004 cm min−1 for electrochemical dissolution of PuO2 at 25°C has been determined. The model was then used to demonstrate the strong effects of the PuO2 size distribution, the silver(I) concentration, the anodic current and some other operational parameters on the dissolution time and the current efficiency. The results of this investigation provide a means for rational design and operation of plutonium-processing systems and stress the importance of operation at the limiting current.
The electrochemical characterization of diamond is just beginning. The study reported here deals with the growth by energy-assisted CVD of impurity-doped diamond electrodes (see Figure) sufficiently conductive for electrochemical measurements. The electrochemical activity of the electrodes towards various analytes, their capacitance and flat-band potentials in several electrolytes, and their photocurrent response are discussed.
Electrochemical oxidation of phenol was studied in a bipolar trickle tower reactor using Raschig ring shaped boron-doped diamond (BDD) electrodes in recirculated batch mode. The model wastewater was prepared with phenol using distilled water. The effects of initial phenol concentration, concentration of Na2 S O4 as a supporting electrolyte, current density, flow rate, and initial pH on the removal efficiency were investigated. The removal of phenol of 200 mgL and chemical oxygen demand (COD) of 480 mgL were achieved with efficiencies of 99.85 and 88.89%, respectively. In the same study, specific energy consumption of 0.676 kWhg phenol removed was determined at the current density of 5 mA cm2. On the other hand, for the initial phenol concentration of 500 mgL and COD of 1,200 mgL, 99.69 and 90.83% removal efficiencies were obtained at the current density of 5 mA cm2, respectively. Microtox toxicity tests were performed to investigate the toxicity reduction potential of BDD anodes, and relatively good toxicity reductions were obtained with respect to the initial values. After determining optimum experimental conditions, petroleum refinery wastewater was also studied by monitoring the destruction of phenol and COD. In this study, phenol removal of 99.53% and COD removal of 96.04% were achieved at the current density of 5 mA cm2. Chemical oxidation studies were also carried out and the results were compared with the electrochemical oxidation studies. According to the whole results, it can be said that Raschig ring shaped BDD anodes exhibited an excellent performance for the degradation of phenol and COD and for the reduction of toxicity.
The electrocatalytic properties of lead dioxide (PbO2) and boron-doped diamond (BDD) anodes were compared for the electrochemical incineration of methyl red, an azo dye, using an electrolytic flow cell with parallel-plate electrodes. The effects of several operating parameters such as current density, hydrodynamic conditions, and pH on the degradation rate and current efficiency were determined. The experimental data indicate that, on PbO2 and BDD anodes, methyl red oxidation takes place by reaction with hydroxyl radicals electrogenerated from water discharge. The electro-oxidation of methyl red was found to behave as a mass-transfer-controlled process, so that the removal rate and current efficiency were enhanced by high flow rates and independent of the pH in the range of 3.0−7.0. It was also observed that the methyl red decay reaction followed pseudo-first-order kinetics with a rate constant that increased slightly with applied current at the PbO2 anode but was essentially independent of current at the BDD anode. From a comparison of the results, it was found that the BDD anode provided a higher oxidation rate and higher current efficiency; however, the two anodes required almost the same energy consumption for the mineralization of methyl red.
A new mathematical approach to the electrochemical treatment of wastewater polluted with organic materials is presented in this work. This model is based on several assumptions related to the reactor-level description, as well as to the mass-transfer and kinetics characteristics. The assumptions allow an easy-to-use model without adjustable parameters to be obtained. The model is applied to the electrochemical treatment of aqueous wastes containing carboxylic acids (formic, oxalic, and maleic) or phenol, using cells with non-active anodes (boron-doped diamond). Good agreement between the experimental and modeling results is obtained in all cases, which validates the assumptions on which the model is based.
Hydroxylation of aromatic compounds has been used extensively as a measure of hydroxyl radicals (OH) formation. In this paper, salicylic acid (2-HBA) was used to trap OH in the process of electrolysis with a couple of Ti-base lead dioxide electrodes in different conditions. Aqueous solution of 2-HBA, a couple of Ti-base lead dioxide electrodes and an AC power were used in the course of OH formation, and then the solution containing 2-HBA and 2,5-dihydroxybenzoic acid (2,5-DHBA) was analyzed by High Performance Liquid Chromatography (HPLC) with fluorescence detector. This method can help us to better understand the reaction mechanism of OH from the viewpoint of quantity.In the same conditions of electrolysis, Total Organic Carbon (TOC) of phenol solutions were detected to identify the effects of some factors during this electrochemical process, because the strong oxidation ability of OH can mineralize the organic pollutants totally and finally achieve the goal of water treatment. The results show that high pH value of electrolyte and high frequency of the AC power are favorable for the generation of OH, however, CO32− is opposite to them.
High-concentration ozone-water can be directly produced with a zero-gap electrolytic cell containing a freestanding perforated boron-doped diamond electrode. For the sake of improving current efficiency for electrochemical ozone-water production, optimization of the electrode configuration was performed. It was proven that the number of holes, hole size, and electrode thickness affect current efficiency. In particular, increasing the number of holes per unit area was the most effective method for improving current efficiency. In regard to hole size, 1 mm diameter was more appropriate than 1.5 mm diameter. Electrode thickness affected the current efficiency, and maximum values were found to be around 0.5-0.6 mm. Based on these results, an electrode optimal for electrochemical ozone-water production was prepared and achieved a maximum current efficiency of 47% in moderate conditions thus far. (c) 2007 The Electrochemical Society.
Boron-doped diamond film grown on a titanium substrate (Ti/BDD) has shown certain stability with superior activity. The causes of its eventual failure may be the large thermal residual stress in the diamond film, which leads to the delamination of the film. A dissociation of TiC layer would collapse the diamond film also. Ti/BDD stability is expected to be improved by coating a thin layer of silicon on the titanium before growing the diamond film at a relatively low temperature. Hot filament chemical vapor deposition was used to grow the diamond film. TiSiBDD electrode has an accelerated lifetime of 320 h, over 20% longer than that of the Ti/BDD. Raman spectroscopy, X-ray diffraction, and scanning electron microscopy examinations demonstrated that the films had well-defined diamond features. TiSiBDD anodes also showed excellent activity in anodic oxidation of typical pollutants like phenol, acetic acid, and maleic acid. A pollutant removal efficiency as high as 90% can be obtained with the effect of pH being insignificant. The current efficiency of slightly over 50% was observed when 90% phenol was degraded in terms of chemical oxygen demand at a current density of 200 A m2.
Peroxodiphosphate salts are strong oxidizing agents that presently can be used as reagents in organics synthesis, cosmetic, agriculture, polluted water treatment, and also as bleaching agents in the detergent industry. They also have potential uses as persulfates substitutes. In this work, a new method for the synthesis of peroxodiphosphate, based on the use of boron-doped diamond electrodes, is described. The procedure developed is able to produce high-purity peroxodiphosphate (no reagents different from phosphate salts are used as raw materials) with a high current efficiency. The efficiencies of the process strongly depend on the pH and on the operating conditions (temperature and current density). The optimum range of pH is 12-13. Current densities over 1000 A m-2, and low temperatures, guarantee high current efficiencies and product conversions. The pH control is considered to be one of the more important operation constraints in the process. Great concentrations of phosphate in the raw materials increase the process efficiencies but they also seem to favor the corrosion of the electrode. Concentrations below 1 M of PO43- are recommended to avoid this problem.
Recently, ozone is used for many purposes as an environmentally friendly oxidant. An ozone production device with high ozone concentration and low production energy is therefore desired. One candidate for such a device is ozone water production in a water electrolysis cell using a solid polymer electrolyte with PbO2 anode catalyst. Such a device would have the advantages of being compact and producing high-concentration ozone water directly through deionized water electrolysis. We have studied ozone water production with different electrode and electrolyte compositions and operation conditions, with the aim of improving ozone production performance. The two electrolytes tested were Nafion 117 and a membrane electrode assembly (MEA) with Pt catalyst on the cathode side of Nafion 117. The two electrodes tested were a single layer of Ti expanded metal and four layers of Ti-expanded metal with different meshes. Ozone water production tests were performed for many hours with changes in temperature, water flow rate, current density, current interruption time, and other factors to optimize experimental conditions. The voltage-current characteristics of water electrolysis cell were improved significantly when the electrode was four layers of Ti-expanded metal and the electrolyte was MEA with Pt catalyst on the cathode. Stable ozone water concentration was obtained after the cell had been operated for about 8 h. The optimum temperature, water flow rate, and current density for ozone water production are 25-30 degrees C, 33 L/h, and 1.0 A/cm(2), respectively. Further, the noninterrupted supply of small current suppressed the performance deterioration of ozone water production by current interruption, and the ozone production energy was reduced by supply of oxygen to the cathode. (c) 2005 The Electrochemical Society.
The electrochemical incineration of glucose mediated by active chlorine in alkaline media has been studied under different electrolysis conditions. For the sake of comparison, the electrolysis has been carried out in the presence of 1 M Na2SO4 + 0.01 M NaOH at Pt, SnO2-Pt composite electrodes and PbO2 electrodes in the absence of sodium chloride. At the first two electrode materials, only partial oxidation could be achieved and complete mineralization was observed only at PbO2 electrode. While the other parameters remain constant, addition of NaCl to the solution causes a sharp increase of the reactivity of glucose and its oxidation intermediates, toward the electrochemical incineration. At a NaCl concentration as low as 1 g/dm, the mediation of the incineration process by active chlorine is already significant. A maximum is achieved at [NaCl] = 5 g/dm (in 0.01 M NaOH). At this sodium chloride concentration, the chemical oxygen demand of glucose solutions has been found to decrease faster, the lower the solution temperature and the higher the current density. This acceleration of the mineralization is accompanied by an increase of faradaic efficiency.
The oxidation of organics, in particular of p-benzoquinone and maleic acid, at high anodic potentials has been studied using a range of anode materials such as noble-metal-based oxides and antimony-doped tin oxides. The influence of the current density was also investigated showing that the oxidation rate of p-benzoquinone increased only slightly with increasing current density. The efficiency of the p-benzoquinone oxidation was found to depend on several properties of the anode material, not just its chemical nature. Furthermore, efficiencies for the partial oxidation of p-benzoquinone using specially prepared noble-metal-oxide-based anodes were found to be only somewhat smaller or even as high as those observed for PbOâ or antimony-doped tin oxide anodes, respectively. The anodic electrolysis of maleic acid solutions was found to decrease the activity of IrOâ for the oxidation of organic compounds. This was not observed when PbO² was employed for the oxidation of maleic acid.