Polyphenazine films as inhibitors of copper corrosion

The polyphenazines poly(brilliant cresyl blue) (PBCB), poly(Nile blue A) (PNB) and poly(safranine T) (PST) have been investigated as corrosion protection films on copper electrodes by open circuit measurements, Tafel plots and electrochemical impedance spectroscopy, complemented by scanning electron microscopy. Pure copper electrodes were initially passivated in sodium oxalate or hydrogen carbonate solutions, to inhibit copper dissolution at potentials where phenazine monomer oxidation occurs, before electropolymerisation by potential cycling. The corrosion inhibition of these films was tested in 0.10 M KCl solution. It was found that, after long immersion times, the best protection efficiency was with PNB films formed on copper passivated in sodium hydrogen carbonate solution

Development of electrochemical oxidase biosensors based on carbon nanotube-modified carbon film electrodes for glucose and ethanol

Functionalised multi-walled carbon nanotubes (MWCNTs) were cast on glassy carbon (GC) and carbon film electrodes (CFE), and were characterised electrochemically and applied in a glucose-oxidase-based biosensor. MWCNT-modified carbon film electrodes were then used to develop an alcohol oxidase (AlcOx) biosensor, in which AlcOx-BSA was cross-linked with glutaraldehyde and attached by drop-coating. The experimental conditions, applied potential and pH, for ethanol monitoring were optimised, and ethanol was determined amperometrically at -0.3 V vs. SCE at pH 7.5. Electrocatalytic effects of MWCNT were observed with respect to unmodified carbon film electrodes. The sensitivity obtained was 20 times higher at carbon film/MWCNT-based biosensors than without MWCNT.http://www.sciencedirect.com/science/article/B6TG0-4RPM7TX-1/1/c7c201831d528c29b469d52592bc656

Eléctrodos de filme de carbono : caracterização e aplicação em sensores e biossensores electroquímicos

Tese de doutoramento em Química (Electroquímica) apresentada à Fac. de Ciências e Tecnologia da Univ. de CoimbraNeste trabalho investigaram-se as propriedades electroquímicas e microestruturais de eléctrodos de filme de carbono com vista à sua utilização em sensores e foram aplicados como eléctrodo-substrato para sensores e biossensores electroquímicos. Os eléctrodos foram preparados a partir de resistências eléctricas de filme de carbono de valores nominais 1,5, 2, 15, 140 e 2 k. A caracterização electroquímica foi efectuada através das técnicas de voltametria cíclica e espectroscopia de impedância electroquímica (EIS) em diferentes soluções de electrólito suporte. Observou-se que os eléctrodos de 1,5 e 2,0 apresentam uma larga janela de potencial e parâmetros cinéticos próximos de reversibilidade após pré-tratamento electroquímico. Os eléctrodos das resistências de 15 e 140 têm uma cinética mais lenta, enquanto que os das resistências de 2 k mostram perfis voltamétricos menos definidos. Da análise da morfologia dos filmes de carbono realizada através de microscopia de força atómica, verificou-se que a uniformidade destes aumenta com a diminuição do valor da resistência nominal. A maior uniformidade foi relacionada com as melhores características electroquímicas obtidas. A estrutura grafítica dos filmes de carbono foi observada por microscopia de Raman confocal e por análise de difracção de raios-X. Os eléctrodos de filme de carbono de resistência de 2 foram modificados com filmes de Nafion e de bismuto para serem usados como sensores electroquímicos de concentrações sub-micromolares de catiões de metais pesados em amostras naturais por técnicas de pré-concentração, exemplificados por cádmio e chumbo. Estudou-se através de EIS a influência do tensioactivo Triton X- I 00 nos resultados experimentais obtidos, utilizado para simular as condições em amostras naturais ambientais, e da modificação dos eléctrodos nas propriedades interfaciais do filme de carbono. Observou-se que os eléctrodos modificados com filmes de bismuto e protegidos com filmes de Nafion facilitam a deposição dos iões metálicos, sugerindo que estes eléctrodos modificados são melhores para a electroanálise dos iões cádmio e chumbo do que os eléctrodos de filmes de carbono modificados apenas com Nafion. Utilizaram-se nanotubos de carbono de paredes múltiplas (MWCNT) funcionalizados em ácido nítrico para modificar eléctrodos de filme de carbono de 2 para o desenvolvimento de biossensores enzimáticos para glucose e etanol. As enzimas foram imobilizadas nos eléctrodos através do método de reticulação com glutaraldeído. Foram observados efeitos electrocatalíticos devidos à presença dos MWCNT em comparação com os biossensores desenvolvidos em eléctrodos sem MWCNT. A sensibilidade obtida com o biossensor modificado com MWCNT foi 20 vezes superior à do biossensor sem MWCNT. Os mediadores redox hexacianoferrato de cobre e poli(vermelho neutro) foram utilizados na modificação dos eléctrodos de filme de carbono e avaliadas as suas características electroquímicas. Os eléctrodos modificados com filmes de PNR foram utilizados, com sucesso, para o desenvolvimento de um biossensor enzimático para a glucose, onde a enzima glucose oxidase foi encapsulada numa matriz de sol-gel oxisilano, a funcionar a potenciais perto de zero onde as interferências são pequenas

Modeling PM2.5 and PM10 Using a Robust Simplified Linear Regression Machine Learning Algorithm

The machine learning algorithm based on multiple-input multiple-output linear regression models has been developed to describe PM2.5 and PM10 concentrations over time. The algorithm is fact-acting and allows for speedy forecasts without requiring demanding computational power. It is also simple enough that it can self-update by introducing a recursive step that utilizes newly measured values and forecasts to continue to improve itself. Starting from raw data, pre-processing methods have been used to verify the stationary data by employing the Dickey–Fuller test. For comparison, weekly and monthly decompositions have been achieved by using Savitzky–Golay polynomial filters. The presented algorithm is shown to have accuracies of 30% for PM2.5 and 26% for PM10 for a forecasting horizon of 24 h with a quarter-hourly data acquisition resolution, matching other results obtained using more computationally demanding approaches, such as neural networks. We show the feasibility of using multivariate linear regression (together with the small real-time computational costs for the training and testing procedures) to forecast particulate matter air pollutants and avoid environmental threats in real conditions

Electrochemical noise and impedance study of aluminium in weakly acid chloride solution

The electrochemical noise (EN) characteristics of pure aluminium in unbuffered potassium chloride solution and with acetic acid/sodium acetate buffer at pH 5.4 and 4.3 have been analysed to throw light on the influence of pH and of the presence of buffer at the aluminium surface on chloride ion-induced corrosion. Comparison has been made with results obtained by electrochemical impedance spectroscopy (EIS) and quantitative deductions made concerning the values of the noise resistance and the magnitude of the electrochemical impedance. Deviations between results obtained by the two experimental techniques are discussed.http://www.sciencedirect.com/science/article/B6TG0-4B2CD8N-1/1/ecb8c688527c2a1bd273f30152f5809

Electrochemical, morphological and microstructural characterization of carbon film resistor electrodes for application in electrochemical sensors

The electrochemical and microstructural properties of carbon film electrodes made from carbon film electrical resistors of 1.5, 15, 140 [Omega] and 2.0 k[Omega] nominal resistance have been investigated before and after electrochemical pre-treatment at +0.9 V vs SCE, in order to assess the potential use of these carbon film electrodes as electrochemical sensors and as substrates for sensors and biosensors. The results obtained are compared with those at electrodes made from previously investigated 2 [Omega] carbon film resistors. Cyclic voltammetry was performed in acetate buffer and phosphate buffer saline electrolytes and the kinetic parameters of the model redox system Fe(CN)63-/4- obtained. The 1.5 [Omega] resistor electrodes show the best properties for sensor development with wide potential windows, similar electrochemical behaviour to those of 2 [Omega] and close-to-reversible kinetic parameters after electrochemical pre-treatment. The 15 and 140 [Omega] resistor electrodes show wide potential windows although with slower kinetics, whereas the 2.0 k[Omega] resistor electrodes show poor cyclic voltammetric profiles even after pre-treatment. Electrochemical impedance spectroscopy related these findings to the interfacial properties of the electrodes. Microstructural and morphological studies were carried out using contact mode Atomic Force Microscopy (AFM), Confocal Raman spectroscopy and X-ray diffraction. AFM showed more homogeneity of the films with lower nominal resistances, related to better electrochemical characteristics. X-ray diffraction and Confocal Raman spectroscopy indicate the existence of a graphitic structure in the carbon films.http://www.sciencedirect.com/science/article/B6THY-4S7BD8R-1/1/06dc918640a4700879aa96e50ac04a8

Enzyme immobilisation on electroactive nanostructured membranes (ENM): Optimised architectures for biosensing

Electroactive nanostructured membranes have been produced by the layer-by-layer (LbL) technique, and used to make electrochemical enzyme biosensors for glucose by modification with cobalt hexacyanoferrate redox mediator and immobilisation of glucose oxidase enzyme. Indium tin oxide (ITO) glass electrodes were modified with up to three bilayers of polyamidoamine (PAMAM) dendrimers containing gold nanoparticles and poly(vinylsulfonate) (PVS). The gold nanoparticles were covered with cobalt hexacyanoferrate that functioned as a redox mediator, allowing the modified electrode to be used to detect H2O2, the product of the oxidase enzymatic reaction, at 0.0 V vs. SCE. Enzyme was then immobilised by cross-linking with glutaraldehyde. Several parameters for optimisation of the glucose biosensor were investigated, including the number of deposited bilayers, the enzyme immobilisation protocol and the concentrations of immobilised enzyme and of the protein that was crosslinked with PAMAM. The latter was used to provide glucose oxidase with a friendly environment, in order to preserve its bioactivity. The optimised biosensor, with three bilayers, has high sensitivity and operational stability, with a detection limit of 6.1 [mu]M and an apparent Michaelis-Menten constant of 0.20 mM. It showed good selectivity against interferents and is suitable for glucose measurements in natural samples.http://www.sciencedirect.com/science/article/B6THP-4SDPX4X-3/1/4f9bf4e20f357feac1d3435f51b9823