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Abstract The current comprehensive review covers four main parts, of which some are presented in the form of a personal account. 1. Anodic oxidation of a) N‐alkyl and N,N‐diallyl carbonyl moieties, b) Azacycloalkyl amides and the effect of ring‐size on the outcome, c) Lactams, d) Sulfonamides, and e) The effect of a substituent R attached to carbonyl (N−CO−R) or sulfonamides (N−SO2R) on their oxidation potentials. 2. Anodic oxidation of aromatic amides, in particular of type Ph2CHCONHAr, lacking hydrogen(s) at the α‐position to nitrogen. They undergo three types of bond‐cleavage, yielding a variety of fragmentation products. 3. a) Anodic oxidation of symmetrical bisamides of type ZCONH(CH2)nNHCOZ (Z=Me, Ph, Ar; n=2–4) under constant current electrolysis, in methanol. For n=3, 4 they afford mostly mono‐ and dimethoxylation products. For n=2 they undergo ′CH2−CH2′ bond cleavage to yield fragmentation products. b) Anodic oxidation of symmetrical bisamides of type ArCONH(CH2)2NHCOAr under controlled potential electrolysis, in acetonitrile, leads to gem‐unsymmetrical bisamides of type ArCONHCH2NHCOMe as the major product, in fair yields. 4. Utilization of the anodic process in organic synthesis to form C−C bonds by both intra‐ and inetrmolecular processes; as well as C−O and C−N bonds for generating heterocycles.

Potassium ferrate(VI) (K2FeO4) as a particularly strong oxidant represents an effective and environmentally friendly waste water treatment material. When produced by anodic oxidation in highly alkaline aqueous solution, the K2FeO4 product is separated and sealed in inert plastic bags with the retention of some liquid phase with high pH. This method proved to be excellent for long-term storage at moderately low temperature (5 °C) for industrial applications. It is still imperative to check the ferrate(VI) content of the product whenever it is to be used. Fe-57 Mössbauer spectroscopy is an excellent tool for checking the ratio of ferrate(VI) to the degradation product iron(III) in a sample. For this purpose, normally the spectral areas of the corresponding subspectra are considered; however, this approximation neglects the possible differences in the corresponding Mössbauer–Lamb factors. In this work, we have successfully determined the Mössbauer–Lamb factors for the ferrate(VI) and for the most common iron(III) degradation products observed. We have found superparamagnetic behavior and low-temperature phase transformation for another iron(III) degradation product that made the determination of the Mössbauer–Lamb factors impossible in that case. The identities of a total of three different iron(III) degradation products have been confirmed.

Abstract Based on the existing literature, active chlorine‐mediated electrochemical oxidation has been extensively studied when Cl‒ is added or Cl‒ is already present in the water matrices, as well as when Cl‒ is released from the target organic pollutants during their degradation. However, no attempts have been published concerning the fate and role of bromide (Br‒) ions released during the anodic oxidation (AO) of organobromine compounds. Therefore, the AO of bromophenol blue dye (BPB) was investigated in a parallel plate flow reactor using a boron‐doped diamond (BDD) anode. The effect of the applied current on the color removal efficiency and mineralization of BPB solution was examined and compared with AO of phenol red (PR) which has a similar molecular structure to BPB (but without Br) in order to understand the role of Br heteroatoms on the mineralization of BPB. Faster and higher mineralization and discoloration were achieved when treated with BPB solution compared to PR under similar experimental conditions. This behavior was associated with the electrogeneration of BrO‒, from the heteroatom Br which is released as the bromide ion (Br‒), during the degradation of BPB. The active bromine species are formed via direct and indirect oxidation approaches which were proposed based on ion chromatography and linear scanning voltammetry analysis.

Abstract Isoxazol(in)es are widely featured structural motifs in natural products, agrochemicals, and pharmaceuticals. The first intermolecular approach for a direct electrochemical synthesis from readily available aldoximes is reported. Isoxazoles and isoxazolines were obtained in yields up to 81 %. The synthesis is carried out in an undivided cell as the simplest electrochemical set‐up and requires only the use of electric current as traceless oxidizing agent. The application of inexpensive and widely available electrode materials in combination with recyclable supporting electrolytes and solvents paves the path for translation of the presented reaction onto preparative scale. This is underlined by successful scale‐up to multi‐gram runs.

Abstract The use of microfluidic electrochemical reactors has been introduced several decades ago, but their application in the field of wastewater treatment is more recent (2010). The parallel development of electrochemical advanced oxidation processes (EAOPs) as promising technologies for effluent treatment make them good candidates to be implemented as thin film cells. This allows favoring the mass transfer, which is particularly interesting for heterogenous electro‐oxidation. Moreover, the energy requirement is reduced, while there is possibility to treat low‐conductivity solutions. This review intends to provide instructions on the main operating parameters to be optimized during the EAOPs treatment. Directions on engineering aspects have been given to overcome the main drawbacks of microreactors, such as fouling, scaling, and low treatment capacity, based on recent encouraging results given in literature. The promising development of hybrid processes that combine electroseparation with electroconversion would also benefit from such reactor designs.

This work presents the electrochemical degradation of the herbicide Diuron by anodic oxidation on a Ti/Ru0.3Ti0.7O2 metal mixed oxide anode using sulfate as the electrolyte. The study includes the influence of Diuron concentration and current density on anodic oxidation. The results evidence a first-order degradation, with the highest capacity achieved at 40 mA cm−2 and at an initial Diuron concentration of 38 mg L−1. Nevertheless, in terms of efficiency and energy demand, the operation at 10 mA cm−2 is favored due to the more efficient and less energy-consuming condition. To discern the optimum design and operation conditions, this work presents the results of a preliminary technical–economic analysis, demonstrating that, to minimize the total costs of the system, it is recommended to seek the most efficient conditions, i.e., the conditions demanding the lowest applied charges with the highest Diuron degradation. At the same time, attention must be given to the required cell voltage to not increase excessively the operating costs.

With the renaissance of chemical electrosynthesis in the last decade, the electrochemistry of hypervalent iodine compounds has picked up the pace and achieved significant improvements. By employing traceless electrons instead of stoichiometric oxidants as the alternative clean “reagents”, many hypervalent iodine compounds were efficiently electro-synthesized via anodic oxidation methods and utilized as powerful redox mediators triggering valuable oxidative coupling reactions in a more sustainable way. This minireview gives an up-to-date overview of the recent advances during the past 3 years, encompassing enhanced electrosynthesis technologies, novel synthetic applications, and ideas for improving reaction sustainability.

An anodic oxidation process with graphite anode coated with lead dioxide (G/β-PbO2) was optimized for the degradation of methylene blue (MB) and the treatment of real textile wastewater. The G/β-PbO2 anode was prepared by the electrochemical precipitation method. The scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses confirmed the successful coating of graphite substrate with the β-PbO2 film. The effect of four independent variables including pH, reaction time, current density, and electrolyte concentration of Na2SO4 on the performance of the electrochemical oxidation system was modeled by using a complete central composite design and was then optimized by genetic algorithm method. The accuracy of the proposed quadratic model by CCD was confirmed with p-value 0.9. The optimum conditions for solution pH, reaction time, current density, and Na2SO4 electrolyte concentration were obtained to be 5.75, 50 min, 10 mA/cm2, and 78.8 mg/L, respectively. In these conditions, the experimental removal efficiencies of MB using G/β-PbO2 and graphite anodes were 96.2% and 68.3%, respectively. The electrochemical removal of MB using both G/β-PbO2 and graphite anodes well followed the pseudo-first-order reaction (R2 > 0.9). Cyclohexane, cyclohexa-2,5-dien-1-ylium, and N-(sec-butyl) aniline were the most abundant intermediates identified by LC-MS analysis. However, the complete mineralization of MB was achieved in 60 min. The optimized anodic oxidation process successfully improved the biodegradability of real textile wastewater (BOD/COD>0.4).

Abstract Most of the active pharmaceutical ingredients like Metoprolol are oxidatively metabolized by liver enzymes, such as Cytochrome P450 monooxygenases into oxygenates and therefore hydrophilic products. It is of utmost importance to identify the metabolites and to gain knowledge on their toxic impacts. By using electrochemistry, it is possible to mimic enzymatic transformations and to identify metabolic hot spots. By introducing charged‐tags into the intermediate, it is possible to detect and isolate metabolic products. The identification and synthesis of initially oxidized metabolites are important to understand possible toxic activities. The gained knowledge about the metabolism will simplify interpretation and predictions of metabolitic pathways. The oxidized products were analyzed with high performance liquid chromatography‐mass spectrometry using electrospray ionization (HPLC‐ESI‐MS) and nuclear magnetic resonance (NMR) spectroscopy. For proof‐of‐principle, we present a synthesis of one pyridinated main oxidation product of Metoprolol.

The climate change imposes to mankind a severe management of CO2 emissions in atmosphere. CO2 valorization through electrocatalysis revealed to be a valuable solution to this global issue. SnO2 is an electrocatalyst widely investigated for its capability to reduce CO2 to formic acid. In particular, mesoporous SnO2 offers a high adsorption capability, resulting in a high catalytic activity. In order to improve its performance, Fe-doping is here investigated for the first time. We observed that Fe-doped SnO2 exhibits a remarkable 100% enhancement of the partial current density for HCOOH production at relatively low overpotentials, although keeping the selectivity unchanged.

TiO2 nanotube arrays (TNAs) prepared by the traditional methods are prone to peeling off from the underlying titanium due to the weak interfacial adhesion between the nanotube layers and Ti substrates, which greatly restricts their applications. Here, 2.5 mm titanium plates are cold rolled to the Ti sheets of various thicknesses by controlling the cold-rolling reduction process. Ti sheets are then anodized in an electrolyte that was composed of water, NH4F, and ethylene glycol. It is discovered that after the cold-rolling process, not only are the pore sizes of the nanotubes smaller, but also the tube length is longer, indicating different growth behavior for the rolled Ti sheets. The results of XRD, EBSD, and metallographic microstructure analysis revealed mechanical anchorage at grain boundaries and decreased F contents, which leads to release stress at the TNAs/Ti interface. Most probably the released stress, finer grain sizes and increased dislocation density are responsible for the improved adhesion.

Anodic TiO2 nanotube (TNT) films show promises for photon-driven catalytic, electricity storage and chemical processes. The film thickness of anodic TNT is known to affect its performance in optical and electronic applications. Also, factors affecting the morphology and dimensions of anodic TNT films are rather well-known. However, the knowledge on phase transition and composition in the growth of anodic TiO2 from the titanium metal is very limited. In this work, the anodization time is controlled in intervals of 10, 60, 300, 1000, 2000 and 5000 s to investigate its effect on phase composition and transition, and the morphology of the anodic TNT during the growth process. Even though the mechanism of anodic TNT formation is still under debate, the scanning electron microscope results support bottom-up tube growth with evidence of a compact layer. It was also found that the Richards growth model is applicable to correlate growth time and film thickness. Finally, the phase transition, crystal orientation and pore formation during the anodic process are further discussed.

A simple and sustainable one-step strategy for the preparation of electron-deficient aryl trifluoromethyl ethers (ArOCF3) from the corresponding phenols by electrochemical synthesis is presented. Anodic oxidation of trifluoromethane sulfinate (Langlois reagent) leads to direct O-trifluoromethylation of phenol-derivatives bearing fluorine, chlorine, bromine and nitrile substituents under mild conditions in yields up to 75% and in gram-scale. This electrochemical protocol provides an economic and green synthesis for an otherwise inaccessible class of molecules without the need for expensive or toxic reagents, oxidants or metal catalysts.

Germanides are an interesting class of two-component systems which consist of metal and germanium. They are similar in their structure with silicides but have the specific properties. The target of the investigation was finding the main anodic electrochemical behaviour mechanisms for magnesium germanide Mn5Ge3 in an Na2SO4 aqueous solution. Electrochemical behaviour of manganese germanide obtained by Czochralski method was investigated by polarization curves and electrochemical impedance spectroscopy methods and accomplished by microscopy data. Individual manganese and germanium were investigated in the same way for comparison. It was established that in the anodic oxidation process germanium is the potential-determining component. The passivation process associated with the formation of surface oxide films was accomplished by the current density oscillations appearing due to the bad adhesion of oxide film to the surface of the sample, its imperfection and discontinuity. The nature of oxide film formed in the polarization process was partially established. The dependence of the anodic behaviour of the sample on the sulphate concentration was established: in the diluted solutions the passivation occurs at more positive potentials than in the concentrated. This phenomenon can be explained by the different mechanisms of anodic oxidation in the solutions of different concentrations.

The oxidation of chlorobenzene (CB) was studied by electrochemical electrolysis using boron-doped diamond (BDD), PbO2 or platine (Pt) as anode and graphite bar as cathode. The effect of applied current density, supporting electrolyte and initial pH value were also studied. The results demonstrated that BDD anode had the best effectiveness and accomplishment of electrochemical degradation of CB compared to PbO2 and Pt anodes. For a current density of 20 mA/cm2 and at pH = 3, the elimination of COD and TOC were about 97% and 98%, respectively, after 360 min of electrolysis with the BDD anode. Pseudo-first order kinetics appears to be the most appropriate to describe the degradation of chlorobenzene. The electrochemical mechanism of chlorobenzene on BDD was proposed based on the identified intermediates.

Lead dioxide-based electrodes have shown a great performance in the electrochemical treatment of organic wastewater. In the present study, modified PbO2 anodes supported on stainless steel (SS) with a titanium oxide interlayer such as SS/TiO2/PbO2 and SS/TiO2/PbO2-10% Boron (B) were prepared by the sol–gel spin-coating technique. The morphological and structural properties of the prepared electrodes were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). It was found that the SS/TiO2/PbO2-10% B anode led to a rougher active surface, larger specific surface area, and therefore stronger ability to generate powerful oxidizing agents. The electrochemical impedance spectroscopy (EIS) measurements showed that the modified PbO2 anodes displayed a lower charge transfer resistance Rct. The influence of the introduction of a TiO2 intermediate layer and the boron doping of a PbO2 active surface layer on the electrochemical degradation of ampicillin (AMP) antibiotic have been investigated by chemical oxygen demand measurements and HPLC analysis. Although HPLC analysis showed that the degradation process of AMP with SS/PbO2 was slightly faster than the modified PbO2 anodes, the results revealed that SS/TiO2/PbO2-10%B was the most efficient and economical anode toward the pollutant degradation due to its physico-chemical properties. At the end of the electrolysis, the chemical oxygen demand (COD), the average current efficiency (ACE) and the energy consumption (EC) reached, respectively, 69.23%, 60.30% and 0.056 kWh (g COD)−1, making SS/TiO2/PbO2-10%B a promising anode for the degradation of ampicillin antibiotic in aqueous solutions.

Abstract Oxidative functionalization of alkenes is a versatile strategy for the preparation of many oxygen‐containing scaffolds, such as epoxides, diols, or carbonyl‐containing compounds. In addition to conventional chemical methods, which rely on the utilization of stoichiometric amounts of oxidizing reagents, some electrochemical procedures have been developed to achieve these transformations. Typical electrochemical procedures employ tailored and often complex redox mediators to achieve the target transformation. Herein we present a modular approach for the synthesis of epoxides, diols, and aldehydes from a single set of reaction components. With sodium bromide as an inexpensive electrocatalyst and water as the oxygen donor, the outcome of the reaction (epoxide, 1,2‐diol, or aldehyde) can be selected by simply tuning the electrolysis conditions. This convenient platform has been accomplished by developing a selective one‐pot three‐step bromide‐electrocatalyzed epoxidation/ring opening/carbon‐carbon cleavage sequence. Its modularity permits the selection of the desired product, as the sequential reaction can be ended when the target compound has been formed. The method has been applied to a diversely functionalized terminal and non‐terminal olefins.

Organic pollutants in domestic sewage, agricultural runoff, industrial wastewater, and contaminated land pose a serious threat to human beings as well as to ecosystems. Anodic oxidation is one of the technologies most commonly used for the degradation of organic pollutants. In this review, we present the current status of promising anodic oxidation technologies for the degradation of organic pollutants, with fundamental insights into anode materials, operating conditions and mechanisms. Firstly, anodes based on metallic Pt, metal oxides (RuO2, IrO2, PbO2 and SnO2), and carbon (BDD and others) are critically reviewed. Secondly, strategies for the effective removal of organic pollutants in wastewater under appropriate operating conditions are systematically investigated. Thirdly, the anodic oxidation mechanism is comprehensively summarized with illustrations of how the organic pollutants can be broken down into small molecules of low or zero toxicity. Finally, we conclude with some future perspectives for application of anodic oxidation.

This study develops the nanostructured superhydrophobic titanium-based materials using a combined preparation method of laser marking step and the subsequent anodizing step. The structural properties were determined using an X-ray diffractometer (XRD) and scanning electron microscope (SEM), while the performance was explored by wear and corrosion tests. The laser marking caused a rough surface with paralleled grooves and protrusions, revealing surface superhydrophobicity after organic modification. The anodizing process further created a titanium oxide (TiO2) nanotube film. Both phase constituent characterization and surface elemental analysis prove the uniform nanofilm. The inert nanosized oxide film offers improved stability and superhydrophobicity. Compared to those samples only with the laser marking process, the TiO2 nanotube film enhances the corrosion resistance and mechanical stability of surface superhydrophobicity. The proposed preparation pathway serves as a novel surface engineering technique to attain a nanostructured superhydrophobic surface with other desirable performance on titanium alloys, contributing to their scale-up applications in diverse fields.

In this study, a new anodic oxidation with a step-bias increment is proposed to evaluate oxidized titanium (Ti) nanostructures on transparent fluorine-doped tin oxide (FTO) on glass. The optimal Ti thickness was determined to be 130 nm. Compared to the use of a conventional constant bias of 25 V, a bias ranging from 5 V to 20 V with a step size of 5 V for 3 min per period can be used to prepare a titanium oxide (TiOx) layer with nanohollows that shows a large increase in current of 142% under UV illumination provided by a 365 nm LED at a power of 83 mW. Based on AFM and SEM, the TiOx grains formed in the step-bias anodic oxidation were found to lead to nanohollow generation. Results obtained from EDS mapping, HR-TEM and XPS all verified the TiOx composition and supported nanohollow formation. The nanohollows formed in a thin TiOx layer can lead to a high surface roughness and photon absorbance for photocurrent generation. With this step-bias anodic oxidation methodology, TiOx with nanohollows can be obtained easily without any extra cost for realizing a high current under photoelectrochemical measurements that shows potential for electrochemical-based sensing applications.

In this work, black phosphorus nanosheets (BPNSs) were prepared by liquid exfoliation in N-methyl-2-pyrrolidone (NMP) and characterized by TEM, AFM, Raman spectroscopy and UV–vis absorption spectroscopy. A novel electrochemical sensor was constructed based on the BPNSs and used to measure pH. As the pH of the solution increases, the oxidation current of the BPNSs decreases. The oxidation degree of the BPNSs may be responsible for their different electrochemical responses to pH. The zeta potentials of the BPNSs also appear to be more negative at higher pH values. The results show that the sensor has a linear response in the pH range 1.0–8.0. The resulting electrochemical sensor could thus be used for accurate pH measurement and was successfully applied to the determination of pH in blood and food samples. The proposed method is simple but is shown to have high accuracy, versatility and applicability.

Molybdenum is one of the valuable metals for the industry; its special properties make it extremely urgent to study the process of separation of molybdenum from other impurities. The article considers the optimization of electrochemical separation of molybdenum from Mo-W system. The electrochemical dissolution of molybdenum and tungsten in solutions of LiCl and NH4NO3 in dimethylsulfoxide was studied using polarization curves and calculation of the efficiency of anodic dissolution of molybdenum in the presence of tungsten. The electrolyte with a composition of 0.5 M LiCl; 5.2 M dimethylsulfoxide; 32.2 M water was selected as an effective solution for the electrochemical separation of molybdenum in the potential range of 1.0‒2.2 V. Results obtained in this study can be used for the development of selective separation method in the molybdenum production.

Photocatalysis has long been touted as one of the most promising technologies for environmental remediation. The ability of photocatalysts to degrade a host of different pollutants, especially recalcitrant molecules, is certainly appealing. Titanium dioxide (TiO2) has been used extensively for this purpose. Anodic oxidation allows for the synthesis of a highly ordered nanotubular structure with a high degree of tunability. In this study, a series of TiO2 arrays were synthesised using different electrolytes and different potentials. Mixed anatase-rutile photocatalysts with excellent wettability were achieved with all the experimental iterations. Under UVA light, all the materials showed significant photoactivity towards different organic pollutants. The nanotubes synthesised in the ethylene glycol-based electrolyte exhibited the best performance, with near complete degradation of all the pollutants. The antibacterial activity of this same material was similarly high, with extremely low bacterial survival rates. Increasing the voltage resulted in wider and longer nanotubes, characteristics which increase the level of photocatalytic activity. The ease of synthesis coupled with the excellent activity makes this a viable material that can be used in flat-plate reactors and that is suitable for photocatalytic water treatment.

The photovoltaic effect in the anodic formation of silicon dioxide (SiO2) on porous silicon (PS) surfaces was investigated toward developing a potential passivation technique to achieve high efficiency nanostructured Si solar cells. The PS layers were prepared by electrochemical anodization in hydrofluoric acid (HF) containing electrolyte. An anodic SiO2 layer was formed on the PS surface via a bottom-up anodization mechanism in HCl/H2O solution at room temperature. The thickness of the oxide layer for surface passivation was precisely controlled by adjusting the anodizing current density and the passivation time, for optimal oxidation on the PS layer while maintaining its original nanostructure. HRTEM characterization of the microstructure of the PS layer confirms an atomic lattice matching at the PS/Si interface. The dependence of photovoltaic performance, series resistance, and shunt resistance on passivation time was examined. Due to sufficient passivation on the PS surface, a sample with anodization duration of 30 s achieved the best conversion efficiency of 10.7%. The external quantum efficiency (EQE) and internal quantum efficiency (IQE) indicate a significant decrease in reflectivity due to the PS anti-reflection property and indicate superior performance due to SiO2 surface passivation. In conclusion, the surface of PS solar cells could be successfully passivated by electrochemical anodization.

This study investigated the fabrication of porous fluorescent SiC using a constant voltage-controlled anodic oxidation process. The application of a high, constant voltage resulted in a spatial distinction between the porous structures formed inside the fluorescent SiC substrates, due to the different etching rates at the terrace and the large step bunches. Large, dendritic porous structures were formed as the etching process continued and the porous layer thickened. Under the conditions of low hydrofluoric acid (HF) concentration, the uniformity of the dendritic porous structures through the entire porous layer was considerably improved compared with the conditions of high HF concentration. The resulting large uniform structure offered a sizable surface area, and promoted the penetration of atomic layer-deposited (ALD) Al2O3 films (ALD–Al2O3). The emission intensity in the porous fluorescent SiC was confirmed via photoluminescence (PL) measurements to be significantly improved by a factor of 128 after ALD passivation. With surface passivation, there was a clear blueshift in the emission wavelength, owing to the effective suppression of the non-radiative recombination rate in the porous structures. Furthermore, the spatial uniformity of emitted light was examined via PL mapping using three different excitation lasers, which resulted in the observation of uniform and distinctive emissions in the fluorescent SiC bulk and porous areas.

Azanucleosides, the sugar‐modified nucleoside analogues, have various biological activities, while their efficient synthetic strategy is still under development. Herein, a novel method for the synthesis of pharmaceutically relevant azanucleosides, β‐anomers of ribo‐azanucleosides, by means of site‐specific anodic C−H activation by using a nitroalkane–lithium perchlorate medium is reported. A mechanistic study of the electrochemical reaction and the armed/disarmed concept from traditional glycochemistry revealed that the 2′‐substituent has a significant effect on the reactivity of prolinol derivative, and suitable carboxylic acid additives can control the reactivity of the intermediate species, an iminium cation equivalent. Finally, this method was demonstrated to be applicable for the synthesis of β‐anomers of ribo‐azanucleosides with all four nucleobases in a stereoselective manner. Efficient synthesis of ribo‐azanucleosides with all four nucleobases was achieved for the first time by means of anodic oxidation. A mechanistic study of the reaction and the armed/disarmed concept from glycochemistry indicated that the acetoxy group at the 2′‐position can decrease the reactivity of the intermediate. Employing trifluoroacetic acid additive for electrosynthesis increased the reactivity of the intermediate, which significantly improved the reaction efficiency. [ABSTRACT FROM AUTHOR]