Remoção de cor em soluções de corantes reativos por oxidação com H2O2/UV

This paper summarizes the result of a degradation test of two azo-reactive dyes (Reactive Blue 214, Reactive Red 243) under UV irradiation in the presence of H2O2. Five different doses of hydrogen peroxide (0 mM, 5 mM, 10 mM, 20 mM and 30 mM) at constant initial concentration of the substrate (100 mg/L) were used. The radiation source were three 15 W-lamps. Complete destruction of the color of the solutions was attained in 40-50 min of irradiation. UV/H2O2 proved capable of complete discoloration and degradation of the above azo reactive dyes.

Construção e aplicação de biossensores usando diferentes procedimentos de imobilização da peroxidase de vegetal em matriz de quitosana

Biosensors were developed by immobilization of gilo (Solanum gilo) enzymatic extract on chitosan biopolymers using three different procedures: glutaraldehyde, carbodiimide/glutaraldehyde and epichlorohydrin/glutaraldehyde. The best biosensor performance was obtained after the immobilization of peroxidase on chitosan with epichlorohydrin/glutaraldehyde. Linear analytical curves for hydroquinone concentrations from 2.5x10-4 to 4.5x10-3 mol L-1 with a detection limit of 2.0x10-6 mol L-1 and recovery of hydroquinone ranging from 95.1 to 105% were obtained. The relative standard deviation was < 1.0 % for a solution of 3.0x10-4 mol L-1 hydroquinone and 2.0x10-3 mol L-1 hydrogen peroxide in 0.1 mol L-1 phosphate buffer solution at pH 7.0 (n=8). The lifetime of this biosensor was 6 months (at least 300 determinations).

Decoloración de alginato de sodio extraído de las algas pardas marinas del género Sargassum con el uso de peróxido de hidrógeno

Hydrogen peroxide bleaching of sodium alginate from seaweeds oh the Sargassum genus was studied. The influence of H2O2 concentration (percentage of H2O2 on a dry weight alginate basis, w/w) and NaOH/H2O2 ratio (% NaOH/% H2O2, both referred to a dry weight alginate basis, w/w) on the molecular weight, color removal and content of Fe3+ ions of bleached alginate samples was investigated by UV and IR spectroscopies, colorimetric determination of Fe3+ ions and vapor pressure osmometry. Higher yield, purity and molecular weight of alginate were obtained using 3% (or less) of hydrogen peroxide and a NaOH/H2O2 ratio of 1.2 for bleaching.

Processamento de pilhas Li/MnO2 usadas

This work presents two recycling processes for spent Li/MnO2 batteries. After removal of the solvent under vacuum the cathode + anode + electrolyte was submitted to one of the following procedures: (a) it was calcined (500 ºC, 5 h) and the calcined solid was submitted to solvent extraction with water in order to recover lithium salts. The residual solid was treated with sulfuric acid containing hydrogen peroxide. Manganese was recovered as sulfate; (b) the solid was treated with potassium hydrogeno sulfate (500 ºC, 5 h). The solid was dissolved in water and the resulting solution was added dropwise to sodium hydroxide. Manganese was recovered as dioxide. The residual solution was treated with potassium fluoride in order to precipitate lithium fluoride.

Recuperação de cobalto e de lítio de baterias íon-lítio usadas

The "active mass" (cathode + anode + electrolyte) of spent Li-ion batteries was submitted to one of the following procedures: (a) it was calcined (500 ºC) and submitted to extraction with water to recover lithium salts. The residual solid was treated with sulfuric acid containing hydrogen peroxide. Cobalt was recovered as sulfate; (b) the "active mass" was treated with potassium hydrogen sulfate (500 ºC) and dissolved in water. Cobalt was precipitated together with copper after addition of sodium hydroxide. Lithium was partially recovered as lithium fluoride. Co-processing of other battery components (aluminum and copper foils) affected negatively the behavior of the recovery procedures. Previous segregation of battery components is essential for an efficient and economical processing of the "active mass".

Extraction, purification and biochemical characterization of a peroxidase from Copaifera langsdorffii leaves

The aim of this work is to obtain, purify and characterize biochemically a peroxidase from Copaifera langsdorffii leaves (COP). COP was obtained by acetone precipitation followed by ion-exchange chromatography. Purification yielded 3.5% of peroxidase with the purification factor of 46.86. The COP optimum pH is 6.0 and the temperature is 35 ºC. COP was stable in the pH range of 4.5 to 9.3 and at temperatures below 50.0 ºC. The apparent Michaelis-Menten constants (Km) for guaiacol and H2O2 were 0.04 mM and 0.39 mM respectively. Enzyme turnover was 0.075 s-1 for guaiacol and 0.28 s-1 for hydrogen peroxide. Copaifera langsdorffii leaves showed to be a rich source of active peroxidase (COP) during the whole year. COP could replace HRP, the most used peroxidase, in analytical determinations and treatment of industrial effluents at low cost.

Uso da casca de coco verde como adsorbente na remoção de metais tóxicos

Green coconut shells were treated with acid, base and hydrogen peroxide solutions for 3, 6, 12 and 24 h for removing toxic metals from synthetic wastewater. The removal of ions by the adsorbent treated with 0.1 mol L-1 NaOH/ 3h was 99.5% for Pb2+ and 97.9% for Cu2+. The removal of Cd2+, Ni2+, Zn2+, using adsorbent treated with 1.0 mol L-1 NaOH/3 h, was 98.5, 90.3 and 95.4%, respectively. Particle size, adsorbent concentration and adsorption kinetics were also studied. An adsorbent size of 60-99 mesh and a concentration of 30-40 g/L for 5 min exposure were satisfactory for maximum uptake of Pb2+, Ni2+, Cd2+, Zn2+ and Cu2+ and can be considered as promising parameters for treatment the aqueous effluents contaminated with toxic metals.

Processos avançados de oxidação de compostos fenólicos em efluentes industriais

In an effort to minimize the impact on the environment, removal of pollutants, such as phenolic compounds, from the industrial wastewater has great importance nowadays because of the high toxicity and low biodegradability of these compounds. This work discusses the different methods to remove these compounds from industrial wastewater, showing their advantages and disadvantages. Advanced Oxidation Process (AOPs) are presented as a promising technology for the treatment of wastewater containing phenolic compounds. Among the AOPs, photolysis, photocatalysis and the processes based on hydrogen peroxide and on ozone are discussed with emphasis on the combined processes and the oxidation mechanisms.

Desenvolvimento de um spot test para o monitoramento da atividade da peroxidase em um procedimento de purificação

In this work we describe both a chromatographic purification procedure and a spot test for the enzyme peroxidase (POD: EC 1.11.1.7). The enzyme was obtained from crude extracts of sweet potatoes and the chromatographic enzyme purification procedure resulted in several fractions. Therefore a simple, fast and economic spot test for monitoring peroxidase during the purification procedure was developed. The spot test is based on the reaction of hydrogen peroxide and guaiacol, which is catalyzed by the presence of peroxidase yielding the colored tetraguaiacol.

Determinação espectrofotométrica de citrato de sildenafil em formulações farmacêuticas

This paper describes a simple and rapid spectrophotometric method for quantitative determination of sildenafil citrate based on its reaction with p-chloranil accelerated by hydrogen peroxide, producing a stable purple compound (λmax= 535 nm). In the absence of peroxide this reaction is very slow. The experimental conditions were optimized by using response surface methodologies. Beer's law is obeyed in a concentration range of 8.52 x 10-5 - 1.70 x 10-3 mol L-1 (r = 0.999). The detection limit was 1.96 x 10-5 mol L-1. The method was successfully applied for the determination of sildenafil citrate in medicines with good accuracy and precision.

Tratamento de águas de refrigeração com peróxido de hidrogênio

Hydrogen peroxide and chlorine are compared as possible disinfectants for water-cooling circuits. To this purpose, samples taken from the cooling system of a steel making plant were treated (at 25ºC and pH values of 5.5 and 8.5) with varying amounts of the two oxidizing agents (0.0 mg/L, 2.0 mg/L and 6.0 mg/L). The results were evaluated through bacterial counting and measurement of corrosion rates upon AISI1020 carbon steel coupons. Bacterial removal and corrosion effects proved to be similar and satisfactory for both reagents.

Estudo da degradação de ranitidina via H2O2 eletrogerado/Fenton em um reator eletroquímico com eletrodos de difusão gasosa

The study of the electrochemical degradation of the ranitidine was developed using an electrochemical reactor with a gas diffusion electrode (GDE) as cathode. The electrolysis experiments was performed at constant current (1 < A < 10) and flow rate of 200 L h-1. The process of drug degradation, chemical/electrochemical and electro-Fenton ways, using electrochemical reactor showed best efficiency at current values of > 4 A. The process reached a production of 630 mg L-1 of the H2O2 at 7 A. The ranitidine concentrations was reduced in 99.9% (HPLC) and chemical oxygen demand (COD) was reduced in 86.7% by electro-Fenton.

Estudio cinético de la descomposición catalizada de peróxido de hidrógeno sobre carbón activado

The kinetic study of decomposition of hydrogen peroxide catalyzed by activated carbon was carried out. The effect of concentrations of reactants and temperature were experimentally studied. Kinetic data were evaluated using differential method of initial rates of reaction. When a typical kinetic law for reactions in homogeneous phase is used, first order of reaction is obtained for hydrogen peroxide and activated carbon, and activation energy of 27 kJ mol-1 for the reaction was estimated. Experimentally was observed that surface of activated carbon is chemically modified during decomposition of hydrogen peroxide, based on this result a scheme of reaction was proposed and evaluated. Experimental data fits very well to a Langmuir- Hinshelwood kinetic model and activation energy of 40 kJ mol-1 was estimated for reaction in heterogeneous phase.

Branqueamento de polpa celulósica kraft de eucalipto com peróxido ácido ativado por molibdênio

Optimum conditions to run the P Mo stage for bleaching eucalyptus kraft pulp were 90 ºC, pH 3.5, 2 h, 0.1 kg/t Mo and 5 kg/t H2O2. The P Mo stage efficiency increased with decreasing pH (1.5-5.5) and increasing temperature (75-90 ºC), time (2-4 h), and hydrogen peroxide (3-10 kg/t) and molybdenum concentration (0.1-0.4 kg/t). The implementation of the P Mo stage, as replacement for the A stage, decreased total active chlorine demand of the OAZDP sequence by 6 kg/t to reach 90% ISO, both in laboratory and mill scale. Such practice resulted in decreased bleaching chemical costs to produce fully bleached pulp of 90% ISO.

Nióbia sintética modificada como catalisador na oxidação de corante orgânico: utilização de H2O2 e O2 atmosférico como oxidantes

In this work synthetic niobia was used to promote the oxidation of methylene blue dye in aqueous medium. The niobia was characterized by N2 adsorption/desorption, XRD and TG measurements. The presence of reactive species on the niobia surface strongly increased the oxidation rate of the methylene blue dye. The reaction mechanism was studied by ESI-MS suggesting that the oxidation of the organic dye involve oxidizing species generated mainly after previous treatment with H2O2. It can be observed that the catalyst is a good material in the activation of gas (atmospheric oxygen) or liquid (hydrogen peroxide) oxidant agent with a total discoloration of the dye solution after only 1 h of reaction.