Aplicação de um corante tiazolilazo como indicador ácido-base e determinação das suas constantes de ionização ácida

The pKa values of the 6-[2´-(6´-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic acid (Me-BDBD) have been determined at 25 °C, in 0.10 mol L-1 NaCl medium by spectrophotometric method. The SQUAD computer program was used to process experimental data in pH range 1.78 - 11.54 and 290 - 720 nm. The pKa values obtained were 4.60 ± 0.04 and 9.48 ± 0.02. The Me-BDBD reagent was applied as indicator in titration of acid-base. The results were compared with phenolphthalein and bromocresol green indicators. Statistical t and F tests indicated that there were no statistically significant differences between the results for indicators with good agreement.

Estudo da sorção do corante catiônico violeta cristal por espuma de poliuretano em meio aquoso contendo dodecilsulfato de sódio

This work presents a detailed study about the sorption of crystal violet (CV) cationic dye onto polyether type polyurethane foam (PUF). The sorption process was based on the formation of an ionic-pair between cationic dye and dodecylsulfate anion (SDS), which presented high affinity by PUF. Set-up employed in the study was built up by adjusting a 200 mg cylinder of PUF to the arm of an overhead stirrer. The system was characterized in relation to equilibrium and kinetic aspects and it was modeled by employing Langmuir and Freundlich isotherms. Obtained results showed that the ratio between SDS and MB concentrations played an important role on the sorption process. According to results found it was possible to retain up to 3.4 mg of dye from 200 mL of a 5.0 x 10-5 mol L-1 CV solution containing 1.25 x 10-4 mol L-1 SDS, which represented a removal efficiency of around 92%.

Adsorção do corante reativo laranja 16 de soluções aquosas por zeólita sintética

Coal fly ash, a waste generated in a coal-fired electric power plant, was used to synthesize zeolite by hydrothermal treatment with NaOH solution. This zeolite was used as adsorbent to investigate the adsorption kinetics and isotherm parameters of the reactive orange 16 (RO16) dye from aqueous solutions at different concentrations (1.3-15.4 mg L-1). Three kinetic models, the pseudo-first-order, second-order, and intraparticle diffusion were used to predict the adsorption rate constants. The kinetics of adsorption of the RO16 dye followed pseudo-second-order kinetics. The adsorption isotherm data were closely fitted to the Langmuir equation. Keywords: coal fly ash; zeolite; reactive dye adsorption.

Reaproveitamento de óxidos de manganês de pilhas descartadas para eletrocatálise da reação de redução de oxigênio em meio básico

The oxygen reduction reaction was studied in alkaline media using manganese oxides obtained from spent batteries as electrocatalysts. Three processes were used to recover manganese oxides from spent batteries. The particles obtained were in the range from 8 to 11 nm. The electrochemical experiments indicated a good electrocatalytic activity toward oxygen reduction using the different samples and showing approximately a direct transference of 4 electrons during the process. Even though all the processes were efficient, the best result was observed for the prepared sample using reactants of low cost.

Adsorção do corante vermelho congo por derivados da o-carboximetilquitosana hidrofobicamente modificados

Hydrophobically modified O-carboxymethylchitosan derivatives were synthesized through a reaction with lauroyl chloride and applied for adsorption of congo red dye. The Langmuir-Freundlich isotherm model was found to be the most suitable one for the VC adsorption and maximum adsorption capacity obtained was 281.97 mg g-1 at a pH value of 7.0 for HL 1.0. The adsorption process follows the pseudo-second-order kinetics and the corresponding rate constants were obtained. The thermodynamic parameters showed that adsorption process is spontaneous (positive ∆Hº) and favorable (negative ∆Gº). The hydrophobic derivatives are able to adsorb the dye even in high pH values.

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.

Remoção de corante por uso de Aspergillus niger AN400 em reator em bateladas sequenciais

A sequential batch reactor (4 L) inoculated with Aspergillus niger was operated in order to remove congo red dye (10 mg L-1). The feeding of the reactor was done to each 7 days. The glucose was added in the concentration of 1 g.L-1 (Stage I) and 0.5 g L-1 (Stage II). The Stage III occurred without glucose addition. The Stage I was great to process, because the system reached the greater dye removal (95%) as well as the kinetic parameters ware the best - K M (0.7 g L-1) and k1 (0.025 h-1).

Remoção dos corantes azul brilhante, amarelo crepúsculo e amarelo tartrazina de soluções aquosas utilizando carvão ativado, terra ativada, terra diatomácea, quitina e quitosana: estudos de equilíbrio e termodinâmica

This work compared activated carbon, activated earth, diatomaceous earth, chitin and chitosan to removal acid blue 9, food yellow 3 and FD&C yellow nº 5 dyes from aqueous solutions with different pH values (2-10). In the best process condition for each dye, equilibrium studies were carried out at different temperatures (from 298 to 328 K) and Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich models were fitted with experimental data. In addition, entropy change, Gibbs free energy change and enthalpy change were obtained in order to verify the thermodynamic adsorption behavior.

Descoloração e degradação do azo corante Vermelho GRLX-220 por ozonização

The discoloration and degradation of the textile dye RED GRLX-220 using the electrochemically generated ozone was investigated. Total discoloration was rapidly achieved in both acid and basic conditions. A pseudo-first order kinetics was observed for discoloration, influenced by pH and ozonation time. A considerable degree of mineralization (60%) was obtained after 30 min of ozonation in alkaline medium. The feasibility of organic matter oxidation during the ozonation process increased in both acidic and alkaline media. The toxicity decreased after the ozonation process, suggesting that the byproducts are less toxic than the parental compound.

Tratamento de resíduos de corante por eletrofloculação: um experimento para cursos de graduação em química

This paper describes the use of a simple experiment of electroflocculation for classroom in Chemistry. Parameters such as electrode material, current density and temperature direct influence the process efficiency. Due to the process low cost and efficient color removal, the methodology proposed has shown good potential for use in wastewater treatment. In addition, the proposed experiment allows discussion about environmental electrochemistry, introduction to concepts of water contamination by industry and university, and also about different alternatives in wastewater treatment used nowadays. Finally, the very easy operation make possible to easy adapt this experiment for high school and elementary school.

Fotoeletrodegradação do corante AO7 utilizando filmes de nanocompósitos de ZnO-TiO2

The Zn-TiO2nanocomposite films were prepared by electrodeposition, using an acidic zinc sulphate solution with TiO2 nanoparticles in suspension. The as-deposited samples have been heated in air at 450 ºC for 6 h. The XRD and SEM analyses pointed out to the metal matrix conversion from Zn to ZnO and a rich morphology of needles-shaped grains. These materials were used on the photoelectrochemical degradation of AO7, which was efficiently degraded, with 40% of color removal, after 2 h period at 1.0 V, under white light irradiation. The apparent first order rate constant of the photoelectrodegradation reaction was 4.12 x 10-3 min-1.

Hidrólise de celulose por catalisadores mesoestruturados NiO-MCM-41 e MoO3-MCM-41

This study was carried out to synthesize, characterize and evaluate the application of mesoestruturated catalysts MCM-41, 5%MoO3-MCM-41 and 5%NiO-MCM-41 in the hydrolysis of microcrystalline cellulose. XRD results indicate that the phase of mesoporous MCM-41 was obtained and that the introduction of metal oxides did not affect this mesoporous phase. About the heterogeneous hydrolysis reaction, it was observed that the increase in temperature results in a higher concentration of glucose and the catalyst 5%MoO3-MCM-41 provides the highest concentrations of glucose.

Avaliação do processo adsortivo utilizando mesocarpo de coco verde para remoção do corante cinza reativo BF-2R

This work used green coconut mesocarp as a bioadsorbent to remove Reactive Gray BF-2R dye. A 2³ factorial design was used to evaluate the influence of the variables adsorbent mass, particle size and stirring speed on the adsorptive process. Kinetic and adsorption equilibrium studies were performed. Results showed that the kinetic equilibrium was reached after 150 min. Using the Langmuir model, a q max of 21.9 mg g-1 and k of 0.30 L g-1 was obtained. The mesocarp of coconut, a residue of agribusiness, proved to be an effective alternative technique for the removal of dye in this study.

Preparação de derivados do lapachol em meio ácido e em meio básico: uma proposta de experimentos para a disciplina de Química Orgânica Experimental

In this educational paper we describe the extraction of lapachol from its natural source according to acid-base concepts in organic chemistry and the use of its derivatives β-lapachone and hydroxy-hydrolapachol to exemplify intramolecular cyclization, carbocation stability, Michael addition reaction and chromatography. The experiments were performed during three different undergraduate organic chemistry laboratory classes using low cost material, while avoiding color reagents for TLC visualization, as well as small-scale column chromatography to isolate the mixture of lapachol and β-lapachone.

Síntese do material mesoporoso MCM-41 usando esponja de água-doce como fonte de sílica

Fresh water sponge was used as a silica source for the synthesis of MCM-41 via the hydrothermal process. The silica was extracted from the sponge by washing with nitric acid and piranha solution. Synthesis of MCM-41 was performed at 100 °C for 5 days and the procedure was optimized, with modifications made to the leaching temperature of the silica and the synthesis of mesoporous material, which was characterized by XRD, FT-IR, SEM and adsorption of N2. The optimal result was achieved at a temperature of 135 °C for 3 days, showing ordered mesoporous material with a surface area of 1080 m² g-1.