Utilization of Sn/Nb2O5 composite for the removal of methylene blue

In this work, the oxidation of methylene blue textile dye in the presence of hydrogen peroxide, using niobium oxide impregnated with different proportions of tin (1, 5 and 10% in mass) as catalyst was studied. The materials were characterized by TPR, XPS, XRD and FTIR. The oxidation tests monitored by ESI-MS showed that the composite containing the higher amount of tin was the most efficient in the removal of the dye. The XRD, XPS, and TPR data presented evidence of the formation of the tin-niobium oxide composite containing Sn0 and supported SnO2.

Desenvolvimento, caracterização e aplicação eletroanalítica de um compósito fluido de adesivo epóxi, grafite e ciclo-hexanona

A fluid conducting composite material prepared from graphite powder, commercial epoxy resin Araldite®, and cyclohexanone has been developed. The composition was optimized considering the mechanical properties as conductivity and adhesiveness using response surface methodology. This work employed cyclic voltammetry and amperometry to investigate the characteristics of such composite electrodes without and with the insertion of Prussian blue in the electrode body (bulk modified electrode). The composite electrodes were also successfully used for the amperometric detection of hydrogen peroxide at 0.0V vs Ag/AgCl.

Spectroscopic characterization of schiff base-copper complexes immobilized in smectite clays

Herein, the immobilization of some Schiff base-copper(II) complexes in smectite clays is described as a strategy for the heterogenization of homogeneous catalysts. The obtained materials were characterized by spectroscopic techniques, mostly UV/Vis, EPR, XANES and luminescence spectroscopy. SWy-2 and synthetic Laponite clays were used for the immobilization of two different complexes that have previously shown catalytic activity in the dismutation of superoxide radicals, and disproportionation of hydrogen peroxide. The obtained results indicated the occurrence of an intriguing intramolecular redox process involving copper and the imine ligand at the surface of the clays. These studies are supported by computational calculations.

Determinação de arsênio em amostras da cadeia produtiva de frangos de corte por espectrometria de absorção atômica com forno de grafite

Chicken meat is largely consumed in human nutrition and it is produced in extremely large scale in some countries, including Brazil. In this work graphite furnace atomic absorption spectrometry was used for determination of arsenic in chicken and chicken production-related samples. These samples were digested employing a microwave-assisted procedure in closed vessels using a 7 mol L-1 nitric acid solution plus concentrated hydrogen peroxide. The concentration range of total As determined in chicken production-related samples varied from 1.30 to 29.8 mg kg-1 of As. The detection and quantification limits reached were 0.055 and 0.182 mg kg-1, respectively (n = 15).

Reciclagem do crômio de resíduos químicos provenientes da determinação de carbono oxidável em fertilizantes orgânicos

This work proposes a separation, recovery and reuse procedure of chemical residues with chromium. This residue was generated by the determination of oxidizable carbon in organic fertilizers samples. The Cr(VI) of the residue was reduced with ethanol and precipitated with NaOH. The Cr(OH)3 precipitate was separated and oxidized to dichromate ions with hydrogen peroxide. This solution was used another time in organic carbon determination. The uses of recycled dichromate solution were appropriated in four successive recycling. The accuracy was proven using potassium hydrogen phthalate and ten organic fertilizer samples. The organic carbon results, determined with recycled solutions, were similar the conventional solution.

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.

Atividade eletrocatalítica de sistemas biomiméticos da enzima catalase

In this work, we describe the immobilization of the dinuclear compound [Cu2(apyhist)2Cl2](ClO4)2 (1) and its derived cations complexes, obtained in water solution or by deprotonation of the imidazolate moiety in the ligand leading to a cyclic tetranuclear species, in the Nafion® membrane on glass carbon electrode surface. After that, we studied the influence of the equilibrium in the electrocatalytic activity towards the reduction of H2O2 in the development of an amperometric sensor for the analytical determination of hydrogen peroxide. This strategy proved successful, and the electrochemical behaviour of the all complexes formed within the Nafion® coatings was characterized. We also provide evidence that its related cyclic tetranuclear imidazolate-bridged complex acts as a catalysts for the intramolecular, two-electron reduction of H2O2.

Actividad catalítica de metales de transición en la descomposición de peróxido de hidrógeno

This paper compares the catalytic activities of some transition metal ions (Fe3+, Co2+, Cu2+, Ni2+, Zn2+) in the H2O2 decomposition in homogenous and heterogeneous processes, including solid mixed systems (Fe-Cu-Co/Al2O3, Fe-Cu/Al2O3, Fe-Co/Al2O3 and Co-Cu/Al2O3). The solids were characterised by X-ray diffraction to explore evolution of phases or possible changes. Different trends of the catalytic activity were observed: in homogeneous medium the most active species was Fe3+, whereas in heterogeneous one the higher activities were shown for Co/Al2O3 and Co-Cu/Al2O3. A strong cooperative effect for the Co-Cu/Al2O3 system was observed, which can be considered as a new catalyst of interest for this type of reactions.

Desenvolvimento e avaliação de eletrodos de difusão gasosa (EDG) para geração de H2O2 in situ e sua aplicação na degradação do corante reativo azul 19

This work reports the development of GDE for electrogeneration of H2O2 and their application in the degradation process of Reactive Blue 19 dye. GDE produced by carbon black with 20% polytetrafluoroethylene generated up to 500 mg L-1 of H2O2 through the electrolysis of acidic medium at -0.8 V vs Ag/AgCl. Reactive Blue 19 dye was degraded most efficiently with H2O2 electrogenerated in the presence of Fe(II) ions, leading to removal of 95% of the original color and 39% of TOC at -0.8 V vs Ag/AgCl.

Adsorção do corante Reativo Azul 19 em solução aquosa por lama vermelha tratada quimicamente com peróxido de hidrogênio

Adsorption of Reactive Blue 19 dye onto activated red mud was investigated. Red mud was treated with hydrogen peroxide (LVQ) and heated at both 400 ºC (LVQ400) and 500 ºC (LVQ500). These samples were characterized by pH, specific surface area, point of zero charge and mineralogical composition. Adsorption was found to be significantly dependent on solution pH, with acidic conditions proving to be the most favorable. The adsorption followed pseudo-second-order kinetics. The Langmuir isotherm was the most appropriate to describe the phenomenon of dye removal using LVQ, LVQ400 and LVQ500, with maximum adsorption capacity of 384.62, 357.14 and 454.54 mg g-1, respectively.

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.

Kalvonpesuprosessit paperiteollisuuden sovelluksissa

Tämän työn tarkoituksena oli löytää tehokas ja taloudellinen pesuaine/pesuaineyhdistelmä kahdelle nanosuodatuskalvolle, joiden läpi on suodatettu paperitehtaan kirkassuodosta ja hiomon kiertovettä. Työssä tutkittiin myös sitä, kestävätkö tutkitut kalvot vetyperoksidia. Työssä havaittiin, että tutkituista kalvoista huokoisempi ei puhdistunut millään tutkituista pesuaineista/pesuaineyhdistelmistä. Tiiviimmän kalvon vesivuo palautui hyvin kahdella tutkituista pesuaineista. Palautuminen oli todennäköisesti seurausta siitä, että pesuaine irrotti lian kalvon pinnasta ja modifioi sen jälkeen kalvon pintaa. Työssä havaittiin myös, että huokoisempi kalvo kestää hyvin toistuvaa vetyperoksidikäsittelyä. Tiiviimpi kalvo puolestaan ei kestä toistuvaa käsittelyä vetyperoksidilla. Vetyperoksidia voidaan kuitenkin käyttää satunnaisesti apuna tiiviimpienkin kalvojen pesussa.

Simultaneous determination of Cd and Pb in antibiotics used in sugar-cane fermentation process by GFAAS

A method has been developed for the simultaneous determination of Cd and Pb in antibiotics used in sugar-cane fermentation by GFAAS. The integrated platform of transversely heated graphite atomizer was treated with tungsten to form a coating of tungsten carbide. Six samples of commercial solid antibiotics were analyzed by injecting 20 µL of digested samples into the pretreated graphite platform with co-injection of 5 µL of 1000 mg L-1 Pd as chemical modifier. Samples were mineralized in a closed-vessel microwave-assisted acid-digestion system using nitric acid plus hydrogen peroxide. The pyrolysis and atomization temperatures of the heating program of the atomizer were selected as 600°C and 2200°C, respectively. The calculated characteristic mass for Cd and Pb was 1.6 pg and 42 pg, respectively. Limits of detection (LOD) based on integrated absorbance were 0.02 µg L-1 Cd and 0.7 µg L-1 Pb and the relative standard deviations (n = 10) for Cd and Pb were 5.7% and 8.0%, respectively. The recoveries of Cd and Pb added to the digested samples varied from 91% to 125% (Cd) and 80% to 112% (Pb).

Photo-Fenton process for treating biological laboratory wastewater containing formaldehyde

Laboratories consume great amounts of hazardous chemicals substances and consequently generate wastewater containing them, for example formaldehyde. This substance is widely utilized to preserve biological samples generating many liters of this residue every year. The present work proposes the use of the photo-Fenton process to treat formaldehyde wastewater using sunlight irradiation. Some aspects were investigated such as the iron source, sample and hydrogen peroxide concentration and also the use of stirred systems. The use of ferrioxalate (0.5 mmol L-1) improved the efficiency of the process in relation to the use of iron nitrate, while at least 1.0 mol L-1 H2O2 is necessary to treat the sample of the 500 mg C L-1. Under these conditions, every formaldehyde detectable was degradeted and 89% of the dissolved organic carbon was removed in two hours of exposure to sunlight. These results are satisfaction considerate for São Paulo State Environmental Agency.

Antioxidant and cytotoxic studies for kaempferol, quercetin and isoquercitrin

The aim of the present study was to investigate a cytotoxic oxidative cell stress related and the antioxidant profile of kaempferol, quercetin, and isoquercitrin. The flavonol compounds were able to act as scavengers of superoxide anion (but not hydrogen peroxide), hypochlorous acid, chloramine and nitric oxide. Although flavonoids are widely described as antioxidants and this activity is generally related to beneficial effects on human health, here we show important cytotoxic actions of three well known flavonoids. They were able to promote hemolysis which one was exacerbated on the presence of hypochlorous acid but not by AAPH radical. Therefore, despite they expected scavenger action over free radicals an oxidants, these compounds could be very lesive to living organisms by acting over erythrocytes and maybe other cellular types.