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The electrochemical behaviour of 2,5-di-(-2-thienyl)-furan (SOS) on Pt has been studied in 0.2 M LiClO 4 +acetonitrile+0.25% (v/v) water solutions by cyclic voltammetry, chronoamperometry and chronopotentiometry. The monomer oxidises at more positive potentials than 0.7 V vs. Ag|AgCl giving a dark-blue film. The most reproducible film weights are obtained by flowing a constant current lower than 1.0 mA cm −2 . The resulting insoluble oxidised films are electroactive and electrochromic. Their control voltammograms exhibit two redox processes attributed to polaronic and bipolaronic states, together with an intermediate reduction shoulder ascribed to radical cation pairs. Electropolymerisation kinetics have been followed by `ex situ' ultramicrogravimetry, giving a maximum productivity of 1.85 mg mC −1 . The oxidised poly(SOS) contains polarons and electroinactive positive charges, both compensated with perchlorate counterions. The reduced poly(SOS) has been obtained in the same electrolyte by applying a constant potential of 0 V to oxidised films. A partial electrodissolution of films is observed during their reduction. The electroinactive charges present in the resulting reduced state cause its insolubility in the medium. Densities, conductivities and solubilities in different organic solvents of both oxidised and reduced poly(SOS) have been determined. Short linear oligomers formed during SOS electropolymerisation have been detected in the saturated solutions of reduced poly(SOS) by mass spectrometry-fast atom bombardment.

We report an experimental and theoretical study of two stable radical adducts of the triphenylmethyl series, 1 and 2, whose composition and molecular structure are distinguished by the content and position of chlorine atoms in phenyls. The electrochemical study through cyclic voltammetry of these open layer species shows the existence of two reversible processes, related to reduction and oxidation, to stable charged species. The chemical oxidation of both radical adducts gives rise to stable cations, whose fundamental state has a biradical triplet electronic structure or a closed shell singlet character, depending on the electronic conjugation between the donor and acceptor electron moieties. The presence of chlorines adjacent to the nitrogen in 1 breaks the conjugation between both halves, facilitating the formation of a triplet electronic state of the cation, while the absence of chlorines in these positions in 2 facilitates partial conjugation and stabilizes the closed shell singlet electronic state of the cation. © 2019 the Owner Societies., Financial support for this research from the MCI (Spain) through projects AGL2017-83599-R and CTQ2015-65770-P is gratefully acknowledged. JMA thanks the Generalitat de Catalunya (Grant 2017SGR348) for financial support, and the Consorci de Serveis Universitaris de Catalunya (CSUC) for providing computational resources.

Two different methods are presented to follow kinetics of redox processes in conducting polymers linked to properties of technological interest: electrodissolution, electrodeposition and electrochromism. Spectroelectrochemical and “ex-situ” microgravimetric measurements allow kinetic magnitudes to be obtained from solid state reactions in polypyrrole and from solution deposition reaction using poly(2,5-di-(2-thienyl) pyrrole.

The electropolymerization of 2,5-di(2-(thienyl)pyrrole) (SNS) on a Pt electrode from ethanolic solution with LiClO4 or LiCl as electrolyte has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). In both media, a quasi-reversible process has been indicated by CV, reversing the scan at low oxidation potentials. Under these conditions, reducible positive charges formed in both oxidized polymers are compensated by the entrance of anions from solution. Elemental analysis reveals that polymers generated at a low oxidation potential by CA contain a 21.03% (w/w) of ClO4- or a 9.56% (w/w) of Cl-. The poly(SNS) doped with Cl- presents higher proportion of reducible positive charges, higher polymerization charge and lower productivity. A much higher electrical conductivity, however, has been found for the poly(SNS) doped with ClO4-. Both polymers are soluble in DMSO, acetone and methanol. The dimer, trimer, tetramer and pentamer have been detected as soluble and neutral linear oligomers by mass spectrometry-fast atom bombardment. The analysis of polymers by infrared spectroscopy confirms the predominant formation of linear molecules with α-α linkages between monomeric units. A condensation mechanism involving one-electron oxidation of all electrogenerated linear and neutral polymeric chains is proposed to explain the SNS electropolymerization.

The feasibility of destruction of organic pollutants in water at near-neutral pH by homogeneous electro-Fenton (EF) process employing a soluble Fe(III)–EDDS complex as catalyst is demonstrated for the first time. The performance of the Fe(III)–EDDS-assisted EF process with carbon-felt or air-diffusion cathodes was evaluated from the degradation of butylated hydroxyanisole (BHA) in sulfate medium. The influence of applied current, pH and Fe(III):EDDS ratio and dosage on BHA decay and mineralization was related to the evolution of H2O2 and iron concentrations. Using Fe(III)–EDDS, up to 50% Fe(II) regeneration was achieved in 10 min, whereas only 23% was transformed using hydrated Fe3+. Almost total removal of BHA was achieved thanks to homogenous Fenton, heterogeneous Fenton with cathodically adsorbed Fe(III), and electrocatalysis. The mineralization partly corresponded to the gradual destruction of EDDS by hydroxyl radical (kabs = 5.22 × 109 M−1 s−1), and involved the formation of 5 oxidation and 6 dimerization or cyclization by-products.

The electrochemical behaviour of the Zn(II)–Zn(Hg) system in aqueous ethylene glycol (EG) solutions containing 5.0 × 10−2 M LiClO4 has been studied by polarography and cyclic voltammetry. The reversible half-wave potentials, the diffusion coefficients and the Walden products for Zn(II) have been polarographically determined. The standard free energies of transfer of 1 mol of Zn(II) ions from water to EG–water mixtures, [Formula: see text], obtained from the reversible half-wave potentials vs. the ferrocene electrode scale, are always negative, indicating a greater stability of Zn(II) in EG–water mixtures than in pure water. The splitting of the [Formula: see text] values into electrostatic and chemical contributions shows that the mixtures are more basic than water. The analysis of the variation of the Walden product with solvent composition indicates an enhancement of the solvent structure in the water-rich region. The diffusion coefficient for Zn in mercury, the transfer coefficients for Zn(II) electroreduction, and the apparent standard rate constants of the Zn(II)–Zn(Hg) system have been determined by cyclic voltammetry. The change in the kinetics with solvent composition is discussed in terms of existing models.

The flow of an anodic current density of 0.5 mA. cm-2 through a 5 mmol/l solution of 2,5-di-(2-thienyl)pyrrole (SNS), in acetonitrile, gives dark-violet and uniform polymer films coating the platinum electrode in presence of different electrolytes. The process is named either electropolymerization or electrogeneration. The new material was insoluble in acetonitrile solutions of different salts. When a cathodic current density of 0.2 mA. cm−2 was applied to the coated electrode, a yellow-green cloud was observed around it. The electrodissolution occurs due to the high, and fast, solubility of the reduced poly(SNS) in the electrolyte. This electrodissolu. m also followed a faradaic process. Deposits of oxidized poly(SNS) films have been further obtained on a Pt electrode by flow of an anodic constant current through a solution containing a salt and the reduced poly(SNS) in acetonitrile. The electrodeposition occurs in presence of different electrolytes. Electrodeposited weights are proportional to the consumed charge: the electrodeposition is a faradaic process. Electrodeposited films are partially electrosoluble in their background solutions. Electrodissolution and electrodeposition from ammonium salts are reverse processes showing the same productivities and mimicking similar processes with inorganic metals. Electrodissolution and electrodeposition processes are being applied to the processability of new actuators and artificial muscles.

Poly(2,5-di-(2-thienyl)-thiophene) films with thickness less than 1.32 μm were electrogenerated on Pt from 5 mM and 20 mM monomer concentrations in 0.1 M LiClO 4 + acetonitrile at constant current. Cyclic voltammograms recorded between 0 and 1.10 V vs. SSCE in the electrolyte showed a redox couple associated to the reduced and oxidized states. The polymer retains its reduced form until 0.6 V, its oxidized form from 0.8 V and a mixture of both states in the potential region 0.6 to 0.8 V. Faradaic impedance measurements for both states were performed at a constant potential between 0.3 and 1.0 V after reducing the electrogenerated polymer at 0 V. A progressive decrease in impedance was always found with increasing the film thickness and more positive potential. An equivalent circuit involving two complex elements is proposed to simulate adequately the Bode plots. Nyquist diagrams and complex plane admittance diagrams obtained. The film resistance is very high for all polymers, suggesting that the mass transport of ClO 4 − ions through the polymer is the rate-determining of the oxidation-doping process. The film capacitance is low for the reduced form and gradually increases when the polymer is oxidized. Deposits obtained from a 20 mM monomer solutions have higher charge-storage capacity than those generated from a 5 mM one, particularly for the oxidized polymer where large amounts of ClO 4 − counterions are accumulated.

Hydrogen peroxide is a pollution-control chemical commonly used as a bleaching agent, as a disinfectant, and as a nonselective oxidant for water purification and in different industrial processes. This paper describes a novel electrochemical method for the generation of HO{sub 2}{sup {minus}} using an alkaline fuel cell (AFC). The system is formed by an undivided cell containing a H{sub 2}-diffusion anode, an O{sub 2}-diffusion cathode, and a KOH solution as electrolyte. It can work in batch or in continuous mode, cogenerating electricity and HO{sub 2}{sup {minus}}, which is formed from the two-electron reduction of O{sub 2} at the cathode. The evolution of cell voltage, current density, HO{sub 2}{sup {minus}} production, and current efficiency with time have been determined when the electrolyte remains quiescent, recirculates through the cell, or is continuously injected to it. This last device yields the best operative parameters, allowing current densities of 130 mA/cm{sup 2} and current efficiencies close to 100% using 1 mol/dm{sup 3} KOH at 20 C. The effect of HO{sub 2}{sup {minus}} upon the anodic and cathodic reactions has been studied by linear sweep voltammetry. Adsorption of this species on the cathode can explain the loss of performance of the AFC with working timemore » using a quiescent electrolyte or under recirculation conditions. The O{sub 2}-diffusion cathode and the AFC showed good reversibility when the cell contained a fresh KOH solution with HO{sub 2}{sup {minus}}.« less

Heterogeneous electron transfer (ET) to o-nitrobenzoic acid has been investigated in NN-dimethylformamide containing tetrabutylammonium perchlorate. Although primary anion radicals undergo fast homogeneous decay, voltammetric measurements allowed the ET rate constant to be determined at various temperatures. These rate constants are abnormally low for an aromatic nitro derivative, even ortho-substituted, as also shown by comparison with the ET rate constant for methyl o-nitrobenzoate, which is at least two orders of magnitude higher. However, the e.s.r. spectrum demonstrates the presence of a hydrogen bond in o-nitrobenzoic acid anion radical, which is not present in the parent molecule, showing that the ET process entails significant structural change. The latter rather than solvent reorganisation around the charge of the anion-radical, localised by the ortho effect, is believed to provide the major contribution to the charge-transfer activation free energy.

Corantes orgânicos têm sido amplamente utilizados em diversos ramos das indústrias de tingimento. Esses compostos são conhecidos por serem bastante tóxicos, mutagênicos, carcinogênico além de causarem poluição estética e danos irreversíveis aos ecossistemas aquáticos e a saúde humana. Estes são considerados contaminantes recalcitrantes devido a sua elevada estabilidade e resistência a bio e foto degradação. Diante deste contexto, a busca por tecnologias capazes de minimizar os efeitos provocados por esses poluentes se faz necessária. Nas ultimas décadas os Processos Eletroquímicos Oxidativos Avançados (PEOA’s) baseados na geração de espécies fortemente oxidantes (radicais ●OH) oferecem abordagens promissoras para a prevenção dos problemas provocados por efluentes industriais. O presente trabalho analisou a degradação e mineralização dos corantes têxteis e o estudo de um efluente real, a fim de avaliar a viabilidade dos PEOA’s tais como Eletrofeton (EF), Fotoeletro-Fenton (FEF) e Oxidação Anódica (OA), bem como a implementação de Fotoeletro-Fenton Solar (FEFS) em uma planta pré-piloto, a fim de estudar o tratamento eletroquímico em escala industrial. No estudo desenvolvido foram comparados o efeito dos PEOA’s na remoção da cor, decaimento do COT e cinética de degradação dos compostos e, ainda para o VC utilizando o SFEFS foram realizados estudos da Eficiência de Corrente de Mineralização (ECM). Os melhores resultados se deram com o tratamento do FEF para todos os corantes estudados. A partir dos resultados obtidos foi possível eleger o FEF como método mais eficiente e promissor para aplicação do tratamento quando comparado aos demais métodos de tratamento, além de comprovar a partir do FEFS que o processo pode ser utilizado em escalas industriais, uma vez que esse método FEF foi aperfeiçoado e a irradiação solar substituiu a lâmpada UVA. Organic dyes have been widely used in various branches of dyeing industries. These compounds are known to be very toxic, mutagenic, cancinogenic only cause aesthetic pollution and irreversible damage to aquatic ecosystems and human health. Are recalcitrant contaminants due to its high stability and resistance to photobleaching and bio. Given this context, the search for technologies that can minimize the effects of such pollutants is required. In recent decades the Electrochemical Oxidation Process Advanced (PEOAs) based on the generation of strongly oxidizing species (radicals ●OH) offer promising approaches for the prevention of problems caused by industrial effluents. This study analyzed the degradation and mineralization of textile dyes and the study of a real effluent in order to assess the feasibility of PEOAs: Electro-Fenton (EF), Photo Electro-Fenton (PEF) and anodic oxidation (AO), and these methods still was studied the Solar Fotoelectro-Fenton (SPEF) in a pre-pilot plant, in order to study the electrochemical treatment on an industrial scale. In the study has compared the effect of PEOAs in the removal of color, TOC and decay kinetics of degradation of the compounds, and also for using the Congo Red (CR) SPEF studies were performed mineralization current efficiency (MCE). The best results are given to the treatment of the PEF for all the studied dyes. From the results it was possible to choose the PEF as the most effective and promising for application of treatment when compared to other methods of treatment, and prove from SPEF that the process can be used in industrial scales, since this method PEF has been improved and solar irradiation replaced the UVA lamp.