Construção de célula eletroquímica para observação de amostras in situ em estereomicroscópio

The electrochemical study of glass like tungsten oxide derivatives requires the construction of special electrodes due to the fact that these glasses are not conductive. Electrodes modified with WO3 change their color when submitted to some potential perturbation. The color change of the electrochromic materials was observed in situ by coupling an electrochemical cell to a stereomicroscope. The constructed cell is versatile and may represent a great contribution to the electrochemical studies of materials, especially in the systems where it is interest to observe the working electrode surface during the electrochemical experiment.

Separation and preconcentration trace amounts of gold by using modified organo nanoclay closite 15A

The application of organo nanoclay 5-(4-dimethylamino-benzylidene) rhodanine-immobilized as a new, easily prepared, and stable solid sorbent for preconcentration trace amounts of Au(III) ions in aqueous solution is presented. The sorption of Au(III) ions was quantitative in the pH range of 2-4, and quantitative desorption occurred instantaneously with 10.0 mL of a mixture containing 0.5 mol L-1 Na2S2O3 and KSCN. Various parameters, such as the effect of pH, breakthrough volume, extraction time, and interference of a large number of anions and cations have been studied. The proposed method has been applied for determination of trace amount of gold in water samples.

Diesel/biodiesel soot oxidation with ceo2 and ceo2-zro2-modified cordierites: a facile way of accounting for their catalytic ability in fuel combustion processes

CeO2 and mixed CeO2-ZrO2 nanopowders were synthesized and efficiently deposited onto cordierite substrates, with the evaluation of their morphologic and structural properties through XRD, SEM, and FTIR. The modified substrates were employed as outer heterogeneous catalysts for reducing the soot originated from the diesel and diesel/biodiesel blends incomplete combustion. Their activity was evaluated in a diesel stationary motor, and a comparative analysis of the soot emission was carried out through diffuse reflectance spectroscopy. The analyses have shown that the catalyst-impregnated cordierite samples are very efficient for soot oxidation, being capable of reducing the soot emission in more than 60%.

Determinação de peróxido de hidrogênio em antisséptico bucal usando um microdispositivo contendo partículas de Azul da Prússia

A simple flow-injection amperometric procedure using a three-electrode-integrated sensor for the determination of H2O2 in antiseptic mouthwash is reported. This method involves the use of a working composite electrode modified with Prussian Blue (PB) particles that was easily adapted as detector in FIA. The best amperometric response was observed for a composite containing 30% of graphite modified with PB particles (GAP) and 70% of pure graphite (GR). The proposed method presents a linear response in the range of 10 to 200 μmol L-1. The detection and quantification limits were 0.8 and 2.6 μmol L-1, respectively.

Highly improved chromium (III) uptake capacity in modified sugarcane bagasse using different chemical treatments

The present paper focuses on improving chromium (III) uptake capacity of sugarcane bagasse through its chemical modification with citric acid and/or sodium hydroxide. The chemical modifications were confirmed by infrared spectroscopy, with an evident peak observed at 1730 cm-1, attributed to carbonyl groups. Equilibrium was reached after 24 h, and the kinetics followed the pseudo-second-order model. The highest chromium (III) maximum adsorption capacity (MAC) value was found when using sugarcane bagasse modified with sodium hydroxide and citric acid (58.00 mg g-1) giving a MAC value about three times greater (20.34 mg g-1) than for raw sugarcane bagasse.

Sodium dodecyl sulfate coated γ-alumina support modified by a new Schiff base for solid phase extraction and flame-AAS determination of lead and copper ions

A simple and fast approach for solid phase extraction is herein described, and used to determine trace amounts of Pb2+ and Cu2+ metal ions. The solid phase support is sodium dodecyl sulfate (SDS)-coated γ-alumina modified with bis(2-hydroxy acetophenone)-1,6-hexanediimine (BHAH) ligand. The adsorbed ions were stripped from the solid phase by 6 mL of 4 M nitric acid as eluent. The eluting solution was analyzed by flame atomic absorption spectrometry (FAAS). The sorption recovery of metal ions was investigated with regard to the effects of pH, amount of ligand, γ-alumina and surfactant and the amount and type of eluent. Complexation of BHAH with Pb2+ or Cu2+ ions was examined via spectrophotometry using the HypSpec program. The detection limit for Cu2+ was 7.9 µg L-1 with a relative standard deviation of 1.67%, while that for Pb2+ was 6.4 µg L-1 with a relative standard deviation of 1.64%. A preconcentration factor of 100 was achieved for these ions. The method was successfully applied to determine analyte concentrations in samples of liver, parsley, cabbage, and water.

A simple square-wave voltammetric method for the determination of scopolamine in pharmaceuticals using a boron-doped diamond electrode

A simple procedure is described for the determination of scopolamine by square-wave voltammetry using a cathodically pretreated boron-doped diamond electrode. Cyclic voltammetry studies indicate that the oxidation of scopolamine is irreversible at a peak potential of 1.59 V (vs. Ag/AgCl (3.0 mol L-1 KCl)) in a 0.50 mol L-1 sulfuric acid solution. Under optimized conditions, the analytical curve obtained was linear (r = 0.9996) for the scopolamine concentration range of 1.0 to 110 µmol L-1, with a detection limit of 0.84 µmol L-1. The method was successfully applied to the determination of scopolamine in pharmaceutical formulations with minimum sample preparation.

Preparation and evaluation of magnetic chitosan particles modified with ethylenediamine and Fe(III) for the removal of Cr(VI) from aqueous solutions

The adsorption of Cr(VI) in aqueous solution by magnetic particles of crosslinked chitosan-ethylenediamine-Fe(III) (MPCh-EDA-FeCL) was studied in a batch system. Fe3+ in the MPCh-EDA-FeCL permitted that adsorption of Cr(VI) occurred with maximum efficiency between pH 3 and 11. The maximum adsorption capacity at pH 7.0 was 81.04 mg g-1 at 25 ºC. The adsorption kinetic process was described by the pseudo-second-order model. Thermodynamic parameters indicated spontaneous, exothermic and chemical adsorption nature. The adsorbent was successively regenerated using a 0.1 mol L-1 NaOH solution. Results were satisfactory for treatment of wastewater from the electroplating industry.

ACIDITY OF MODIFIED MORDENITES SYNTHESIZED FROM RICE HUSK SILICA AND CATALYTIC TRANSFORMATION OF METHYLBUTYNOL

Mordenite (MOR) was synthesized using rice husk silica and modified by base (B), acid (A) or acid-base (AB) and converted to H-form. The modification did not destroy the MOR structure but increased surface area and generated mesopores. Lewis acidity of the parent and modified MOR samples investigated by aluminum NMR and NH3-TPD showed a decrease in the following order: HMOR > BMOR > ABMOR > AMOR. For the catalytic transformation of methylbutynol, ABMOR provided the highest conversion and selectivity of products from acid sites.

SÍNTESE E CARACTERIZAÇÃO DE COMPÓSITOS ORGÂNICO-INORGÂNICOS MACROPOROSOS PARA O SENSORIAMENTO DE H2O2

Electrodes modified with poly(5-amino-1-naphthol)/Prussian blue (poly(5-NH2-1-NAP)/PB) hybrid films are able to electrochemically reduce H2O2 in medium containing an excess of Na+ cations. This is an important advantage for biosensing applications over electrodes in which only conventionally (electro) deposited Prussian blue is present. Consequently, the aim of this work was to examine the application of templates of ordered arrays of colloidal poly(styrene) spheres (800, 450 and 100 nm in diameter) to produce inverse opal structures of poly(5-NH2-1-NAP)/PB hybrid platforms, in an effort to study the influence of the increase in surface area/volume ratio and higher exposition of the mediator active sites on material performance during H2O2 determination employing the different sized porous structures. Moreover, since the accentuated hydrophilic character of poly(5-NH2-1-NAP)/PB also allows H2O2 electrochemical reduction in inner active sites, issues concerning the amount of mediator electrodeposited on the electrode were also reflected in the observed results.

HYDROLYTIC DEGRADATION BEHAVIOR OF PLLA NANOCOMPOSITES REINFORCED WITH MODIFIED CELLULOSE NANOCRYSTALS

Bionanocomposites derived from poly(L-Lactide) (PLLA) were reinforced with chemically modified cellulose nanocrystals (m-CNCs). The effects of these modified cellulose nanoparticles on the mechanical and hydrolytic degradation behavior of polylactide were studied. The m-CNCs were prepared by a method in which hydrolysis of cellulose chains is performed simultaneously with the esterification of hydroxyl groups to produce modified nanocrystals with ester groups. FTIR, elemental analysis, TEM, XRD and contact angle measurements were used to confirm and characterize the chemical modifications of the m-CNCs. These bionanocomposites gave considerably better mechanical properties than neat PLLA based on an approximately 100% increase in tensile strength. Due to the hydrophobic properties of the esterified nanocrystals incorporated into a polymer matrix, it was also demonstrated that a small amount of m-CNCs could lead to a remarkable decrease in the hydrolytic degradation rate of the biopolymer. In addition, the m-CNCs considerably delay the degradation of the nanocomposite by providing a physical barrier that prevents the permeation of water, which thus hinders the overall absorption of water into the matrix. The results obtained in this study show the nanocrystals can be used to reinforce polylactides and fine-tune their degradation rates in moist or physiological environments.

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).

Influence of the medium (strongly acid or basic) over the electrochemical properties of the nitrate selective electrode

A nitrate selective electrode was prepared for use in an aggresive medium (high acidic or basic concentration). It is demonstrated that the depending E graph with respect to pNO3- has not a Nernstian response in concentration acidic range upper 0.1 mol/L H2SO4. The observed behaviour is supposed to be due to the formation of a dimeric anion HN2O6-.

Use of a Ca-selective electrode in the determination of total Ca in the production of crude sugar. Preliminary studies

The determination of the total calcium in juice, syrups, and other products of the sugar industry is investigated. Total calcium and free calcium is determinated by AAS and employing Ca-selective electrode respectively. A coefficient is obtained for the relation of total calcium with respect to free calcium. The coefficient is employed to determine the content of total calcium in accordance with the following equation.

Effect of alcohol concentration and electrode composition on the ethanol electrochemical oxidation

The electrochemical oxidation on platinum and platinum rhodium bimetallic electrodes was studied by Differential Electrochemical Mass Spectrometry for several ethanol concentrations in solution. It is found that increasing the ethanol concentration the production of the partially oxidized products (acetaldehyde) increases as the concentration increases. On the other hand, addition of 25% at. of rhodium increases the full oxidation to CO2. Another interesting result observed is a correlation between the intensity of the dehydrogenations peak at 0.3 V vs. RHE and the CO2 yield for the different ethanol concentration studied.