Alzira Maria Serpa Lucho

Electrochemical studies of propargyl alcohol as corrosion inhibitor for nickel, copper, and copper/nickel (55/45) alloy

Abstract The electrochemical behaviour of copper, nickel and copper/nickel (Cu55/Ni45) alloy in 0.50 M H2SO4 in the absence and presence of propargyl alcohol has been studied. The results indicate that the electrochemical behaviour of the copper/nickel alloy is similar to that of nickel. The interaction between the electrode surface and the organic compound is a relatively fast process and depends on the adsorption potential and alcohol concentration. Anodic currents associated with the electrooxidation of the metals decrease in the presence of propargyl alcohol. Differences in inhibition experience by the three electrodes are discussed in terms of cyclic voltammetry, potentiometry and impedance measurements.

Electrooxidation of nitrite on a silica-cerium mixed oxide carbon paste electrode.

A silica-cerium mixed oxide (SiCe) was prepared by the sol-gel process, using tetraethylorthosilicate and cerium nitrate as precursors and obtained as an amorphous solid possessing a specific surface area of 459 m(2) g(-1). Infrared spectroscopy of the SiCe material showed the formation of the Si-O-Ce linkage in the mixed oxide. Scanning electron microscopy/energy dispersive spectroscopy indicated that the cerium oxide particles were homogenously dispersed on the matrix surface. X-ray diffraction and (29)Si solid-state nuclear magnetic resonance implied non-crystalline silica matrices with chemical environments that are typical for silica-based mixed oxides. X-ray photoelectron spectroscopy showed that Ce was present in approximately equal amounts of both the 3+ and 4+ oxidation states. Cyclic voltammetry data of electrode prepared from the silica-cerium mixed oxide showed a peak for oxidation of Ce(3+)/Ce(4+) at 0.76 V and electrochemical impedance spectroscopy equivalent circuit indicated a porous structure with low charge transfer resistance. In the presence of nitrite, the SiCe electrode shows an anodic oxidation peak at 0.76 V with a linear response as the concentration of the analyte increases from 3×10(-5) at 3.9×10(-3) mol L(-1).

Anilinepropylsilica xerogel used as a selective Cu (II) adsorbent in aqueous solution

The metal ion adsorption properties of the microporous hybrid anilinepropylsilica xerogel were studied using divalent copper, zinc, and cadmium ions in aqueous solutions in concentrations ranging from 10(-4) up to 5x10(-3) moll(-1). At low concentrations the surface of the solid phase presents selectivity for Cu (II), even in competitive conditions. This preferential sorption ability for copper in relation to zinc and cadmium ions was interpreted by considering the xerogel morphology.

Thin film of copper hexacyanoferrate dispersed on the surface of a conducting carbon ceramic material, SiO2/ZrO2/C-graphite: characteristics and electrochemical studies

O material SiO2/ZrO2/C-graphite (SZC) foi preparado pelo metodo sol-gel apresentando duas composicoes, designadas por: (a) SZC30 (SiO2= 50%, ZrO2= 20%, C= 30%) e (b) SZC20 (SiO2 =60%, ZrO2= 20%, C= 20%) em % m. A estrutura do material foi investigada por difracao de raios X (XRD), microscopia eletronica de transmissao de alta resolucao (HR-TEM) e espectroscopia de fotoeletrons excitados por raios X (XPS). A condutividade eletrica dos discos prensados destes materiais foi 4 e 18 S cm-1 para SZC20 e SZC30, e a area superficial especifica (determinado pelo metodo BET) dos compositos carbono cerâmico foi 45 e 12 m2 g-1, respectivamente. Um filme fino de hexacianoferrato(II) de cobre foi formado in situ na superficie do material contendo 30 % (em massa) de grafite (SZC30). A espessura do filme foi estimada como sendo 110 nm. O potencial medio para o processo redox foi dependente da concentracao de eletrolito suporte na faixa de 0,1 a 1,0 mol L-1 de KCl e a resistencia de transferencia de carga, determinada por espectroscopia de impedância eletroquimica (EIS), foi de 23,8 ohm cm2.

Evidence of a polymeric film formation from furfural electrooxidation on platinum platinized electrode in acetonitrile

Abstract A polymeric film formed from furfural (2‐furancarboxaldehyde) dissolved in acetonitrile was observed on Pt/Pt electrodes. Three different electrochemical methods such as cyclic voltammetry (CV), chronopotentiometry, and chronoamperometry were used to grow the film. The polymeric film was perfectly visible on the electrode surface, however, scanning electron microscopy (SEM) photographs were taken in order to confirm the presence of the film. The structure of the polymer according to the data obtained from IR spectroscopic data is also presented. The influence of the film on the electrochemical behavior of the platinum electrode was characterized by comparing the I(E) curves in aqueous 0.50 mol/L H2SO4 solutions. After recovering the voltammograms confirm the modification of the electrode surface. Basically, a strong inhibition of hydrogen reduction/oxidation was observed in the cathodic potential range. However, at potentials more positive than 1.10 V (SCE) the stability of the film was poor, suggesting a degradation of the polymer. The electrochemical impedance spectroscopy (EIS) responses of modified Pt/Pt electrodes coated with polyfurfural were also placed in aqueous sulfuric acid. The presence of the film on the electrode surface was characterized by a capacitive behavior at low frequencies.

Electrochemical polymerization of furfural on a platinum electrode in aqueous solutions of potassium biphthalate

Three different electrochemical methods confirm the growth processes of polyfurfural on platinum electrodes in aqueous solutions. The electrochemical oxidative polymerization of furfural occurs only with 0.10 mol L-1 potassium biphthalate as the supporting electrolyte. Electrochemical and spectroscopic methods are employed to characterize the polymeric film produced. Based on spectroscopic data, a polymeric structure involving furfural and biphthalate anions is discussed.

Polyfurfural Film Synthesized by Electrochemical Reduction of Furfural on Bright Platinum Electrode

The electroreduction of furfural (2‐furancarboxaldehyde) was confirmed on bright platinum electrode in acetonitrile solutions. The product synthesized was an organic film with good adherence and electrical conductivity. Three electrochemical methods such as CV, chronopotentiometry and chronoamperometry were used in this process. SEM photographs were conclusive to confirm the presence of the film on the electrode surface. The IR and 13C NMR spectra of the resin obtained galvanostatically suggest a complex structure with the presence of the furfural and organic solvent molecules.

Electrochemical Oxidation, Adsorption and Quantification of 1,2-Benzopyrone Employing a Glassy Carbon Electrode

The electrooxidation of 1,2-benzopyrone (BP) was assessed via linear voltammetry and electrochemical impedance spectroscopy on a glassy carbon electrode in dibasic potassium phosphate buffer. The oxidation process for BP requires one electron and forms a ketone. This oxidation product was adsorbed by the electrode surface to form a film that blocks active sites and increases in thickness over consecutive measurements. The oxidation conditions were optimized using factorial design and Doehlert matrices. This electrochemical method was compared to high performance liquid chromatography (HPLC), which has a detection limit of 26.4 µmol L-1 for BP. The voltammetric results were statistically similar to those from HPLC; however, the method was faster, simpler, more easily acquired, more sensitive, and required less organic solvent.

ELETRODOS DE FTO MODIFICADOS POR ELETRODEPOSIÇÃO DIRETA DE OURO: PRODUÇÃO, CARACTERIZAÇÃO E APLICAÇÃO COMO SENSOR ELETROQUÍMICO

Chemically modified electrodes have been studied to obtain new and better electrochemical sensors. Transparent conductive oxides, such as fluorine-doped tin-oxide (FTO), shows electrical conductivity comparable to metals and are potential candidates for new sensors. In this work, FTO was modified by gold electrodeposition from chlorine-auric acid solution using cyclic voltammetry (CV) technique. A set of different materials were produced, varying the scan number. Scanning electron microscopy and electrochemical impedance spectroscopy were performed for the characterization of electrodes surfaces. From this analysis was possible to observe the resistive, capacitive and difusional aspects from all kind of modified electrodes produced, establishing a relationship between this parameters and the scan number. The electrode with 100 scans of CV presented better characteristics for an electrochemical sensor; it has the lowest global impedance and rising of capacitive behavior (related to electrical double layer formation) at lower frequencies. This electrode was tested for paracetamol and caffeine detection. The results showed a high specificity, decreased oxidation potential (0.58 V and 0.97 Vvs. SCE, for paracetamol and caffeine, respectively) and low detection limits (0.82 and 0.052 µmol L-1).

Electrode Material Containing Graphite Incorporated to an Amino-Functionalized Polydimethylsiloxane Network for the Detection of Copper

Graphite was incorporated to a polydimethylsiloxane (PDMS) polymer network functionalized with amino groups to obtain an electrode material and used to detect copper ions in aqueous solutions and sugarcane spirit. The polymer network was prepared with PDMS, 3-aminopropyltrimethoxysilane (APTMS), tetraethyl orthosilicate (TEOS) with addition of graphite to obtain the electrode material. The materials were prepared with different mass concentrations of PDMS: 0, 3, 6, 12 and 18%; and characterized by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). Quasi-reversible behavior was found when studying the [Fe(CN)6] redox probe and were electrochemically stable up to 100 consecutive cycles. Electrochemical impedance measurements showed a second time constant at high frequencies for the PDMS electrodes, indicating a second phase in the polymer network with resistive properties, probably due to an increase in the material polymerization resistance. Square wave voltammetry studies were conducted with these electrodes to detect copper(II) ions in aqueous solution. The electrode proposed was applied to determine Cu in a real sample, sugarcane spirit. The PDMS electrodes prepared here presented a potential to be applied as electrochemical sensors for detecting copper ions.