F. Cases

A voltammetric and FTIR–ATR study of the electropolymerization of phenol on platinum electrodes in carbonate medium: Influence of sulfide

Abstract Voltammetry and FTIR–ATR techniques have been employed to investigate polyphenol films formed on platinum surfaces by electrochemical oxidation of phenol. The media used in the electropolymerization were aqueous carbonate solutions, with and without Na 2 S. The polymeric films created are not permeable to ferrocyanide and ferricyanide species and present low water mobility. The presence of sulfide in the electropolymerization solution enhances these characteristics. The amount of sulfur detected by an energy dispersive X-ray detector (EDX) in the polymeric films created in the presence and in the absence of sulfide in the solution is very similar. Thus, the sulfur present in the polymer created in solutions with a sulfide concentration up to 10 −3 M is not representative. A strong stretching vibration band at 900–1150 cm −1 is obtained in the IR spectrum that can be associated to the ether linkages of the phenolic rings (ue605Cue5f8Oue5f8Cue605).

Characterization and stability of doped SnO2 anodes

Doped tin dioxide electrodes have been prepared by a standard spray pyrolysis technique. The electrochemical behaviour of these electrodes has been investigated by cyclic voltammetry in sulphuric acid using the Fe2+/Fe3+ redox couple system as test reaction. Oxygen evolution has been used to study the stability of doped SnO2 electrodes. The SnO2 electrodes doped with antimony and platinum exhibit the highest stability. XPS analysis shows that the oxidation state of Sn, Sb and Pt are +4, +3 and +2, respectively, the probable species being SnO2, Sb2O3 and PtO.

Corrosion behaviour at the interface of steel bars embedded in cement slurries: effect of phenol polymer coatings

Direccion General de Ensenanza Superior e Investigacion Cientifica (PB97-0130); Generalitat Valenciana (GV-1159/93) AE97-2).

Influence of electrochemical reduction and oxidation processes on the decolourisation and degradation of C.I. Reactive Orange 4 solutions

The electrochemical treatment of wastewaters from textile industry is a promising treatment technique for substances which are resistant to biodegradation. This paper presents the results of the electrochemical decolourisation and degradation of C.I. Reactive Orange 4 synthetic solutions (commercially known as Procion Orange MX2R). Electrolyses were carried out under galvanostatic conditions in a divided or undivided electrolytic cell. Therefore, oxidation, reduction or oxido-reduction experiences were tested. Ti/SnO(2)-Sb-Pt and stainless steel electrodes were used as anode and cathode, respectively. Degradation of the dye was followed by TOC, total nitrogen, COD and BOD(5) analyses. TOC removal after an oxidation process was higher than after oxido-reduction while COD removal after this last process was about 90%. Besides, the biodegradability of final samples after oxido-reduction process was studied and an improvement was observed. UV-Visible spectra revealed the presence of aromatic structures in solution when an electro-reduction was carried out while oxido-reduction process degraded both azo group and aromatic structures. HPLC analyses indicated the presence of a main intermediate after the reduction process with a chemical structure closely similar to 2-amine-1, 5-naphthalenedisulfonic acid. The lowest decolourisation rate corresponded to electrochemical oxidation. In these experiences a higher number of intermediates were generated as HPLC analysis demonstrated. The decolourisation process for the three electrochemical processes studied presented a pseudo-first order kinetics.

Voltammetric and in situ FTIRS study of the electrochemical oxidation of aniline from aqueous solutions buffered at pH 5

The electrochemical oxidation of aniline at low concentration was carried out in phosphate buffer solutions of pH 5. Both electrochemical and spectroscopic results indicate that during the initial stages of aniline oxidation, a dimerisation process takes place. The dimer has been identified as p-aminodiphenylamine (ADPA). No evidence supporting the formation of other dimerisation products, such as benzidine or hydrazobenzene has been found. The hydrolysis of ADPA seems to be a very slow process at pH 5 and, consequently, the formation of hydroquinone/p-benzoquinone has not been observed. ADPA is poorly soluble in aqueous medium and a part of these species precipitates on the electrode surface when formed. This precipitated dimer could act as an active centre for the further growth of the polymeric chains.

Electrochemical behaviour of amino acids on Pt(h,k,l): a voltammetric and in situ FTIR study. Part 1. Glycine on Pt(111)

Abstract A spectroelectrochemical study of the adsorption and oxidation of glycine on a Pt(111) electrode has been carried out in 0.1 M HClO4 solution. Two types of adsorbate were identified. On the one hand, strongly adsorbed cyanide which comes from the oxidative adsorption of the molecule. This adsorbate has been isolated and characterized. On the other hand reversibly adsorbed glycinate anions, which adsorb at potentials above 0.3 V, have been detected. As in the case of acetate anions, glycinate is two-fold coordinated to the Pt(111) surface through the carboxylate group. The analysis of the potential dependent band centre frequencies and integrated band intensities suggests that lateral interactions between adsorbed glycinate anions are at the origin of the small frequency shift observed with increasing potential.

Dissociative adsorption of ethanol on Pt (h, k, l) basal surfaces

This work shows that Pt surfaces with different crystalline orientations are able to break the C-C bond of this C2 molecule, producing various types of adsorbed residues

Irreversible adsorption of methanol on Pt(110) in carbonate solution

Abstract An electrochemical study of the adsorbed species formed from the irreversible adsorption of methanol on a Pt(110) electrode in carbonate solution has been carried out. The adsorbed species may be assigned to adsorbed CO. These adsorbed species produce a structural surface modification of a Pt(110)-(1 × 1) surface in the same way as direct irreversible adsorption of CO.

Study of the electrochemical oxidation and reduction of C.I. Reactive Orange 4 in sodium sulphate alkaline solutions.

Synthetic solutions of hydrolysed C.I. Reactive Orange 4, a monoazo textile dye commercially named Procion Orange MX-2R (PMX2R) and colour index number C.I. 18260, was exposed to electrochemical treatment under galvanostatic conditions and Na2SO4 as electrolyte. The influence of the electrochemical process as well as the applied current density was evaluated. Ti/SnO2-Sb-Pt and stainless steel electrodes were used as anode and cathode, respectively, and the intermediates generated on the cathode during electrochemical reduction were investigated. Aliquots of the solutions treated were analysed by UV-visible and FTIR-ATR spectroscopy confirming the presence of aromatic structures in solution when an electro-reduction was carried out. Electro-oxidation degraded both the azo group and aromatic structures. HPLC measures revealed that all processes followed pseudo-first order kinetics and decolourisation rates showed a considerable dependency on the applied current density. CV experiments and XPS analyses were carried out to study the behaviour of both PMX2R and intermediates and to analyse the state of the cathode after the electrochemical reduction, respectively. It was observed the presence of a main intermediate in solution after an electrochemical reduction whose chemical structure is similar to 2-amino-1,5-naphthalenedisulphonic acid. Moreover, the analysis of the cathode surface after electrochemical reduction reveals the presence of a coating layer with organic nature.

Electrochemical oxidation of ethanol on Pt(hkl) basal surfaces in NaOH and Na2CO3 media

Abstract The electrooxidation of ethanol as well as its irreversible adsorption on platinum single crystal electrodes have been studied in NaOH and Na 2 CO 3 media. Pt(110) and Pt(100) electrodes show deactivation for oxidation of bulk ethanol in both media, caused mainly by a structural surface modification of the electrode surface. However, in NaOH solution Pt(lll) exhibits the best behaviour on ethano] oxidation showing the highest current density and the most stable surface. From the SNIFT-IR spectra adsorbed CO is the main poisoning species in the irreversible adsorption of ethanol on Pt(110) and Pt(100); on Pt(111) only a very weak band of adsorbed CO is observed. From the FT-IR spectra obtained during the oxidation of ethanol on Pt(HO), Pt(100) and Pt(111) electrodes, acetate anions have been identified as the main soluble oxidation product.