Two types of manganese oxide were investigated for the removal/degradation of Orange G (OG) dye in aqueous solution. One manganese oxide (pyrolusite) was obtained commercially and the other (birnessite) was prepared according to the polyol method by means of the oxidation of Mn II hydroxide by H 2 O 2 . Both materials were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM), and nitrogen adsorption/desorption at 77 K. The effects of agitation time, pH, and MnO 2 dose on the degradation of OG by the birnessite and pyrolusite were evaluated. Approximately 90 and 99% decoloration of OG (10 mg L -1 ) was obtained after 30 min of stirring with 0.20 g L -1 of birnessite or pyrolusite, respectively. The decoloration and increased intensity of absorbance bands in the UV-visible spectrum were indicative of a degradation process that followed pseudo-first order kinetics. The findings demonstrated the high efficiency of different types of manganese oxides for removal of this organic pollutant from waters.
A new method has been developed to determine trace levels of organophosphorus pesticide parathion-methyl in water samples by using dispersive liquid-liquid microextraction (DLLME), followed by gas chromatograph coupled with electron capture detector (GC/ECD) analysis. The optimized and validated method showed high extraction recovery (101.1%), high enrichment factor (57.3), low limits of detection and quantification, 0.083 and 0.250 μg L -1 , respectively. The established DLLME-GC/ECD method has been successfully applied for the evaluation of the photodegradation of the parathion-methyl by UV 254nm radiation in different conditions of pH and temperature. The parathion-methyl photodegradation at pH 3 and 35 °C achieved > 99.5% after 120 min of exposition. For this condition, it was observed the kinetic rate of 0.0515 min -1 , the quantum yield of 1.22 × 10 -5 mol Einstein -1 and a half-life time of 13.46 min. All experimental conditions tested proved to be strongly influenced by pH and temperature. The application of the optimized process in distilled and drinking water spiked with parathion-methyl provided residues of this pesticide at levels below the maximum permitted by Brazilian legislation, which is 9.0 μg L -1 .
Discute-se, neste relato, a aplicação e o resultado de uma Sequência Didática (SD) realizada com os alunos do terceiro ano do ensino médio da Educação de Jovens e Adultos (EJA), com a temática “agrotóxicos, as novas legislações e impactos socioambientais”. Por meio da metodologia dos Três Momentos Pedagógicos (3MP) para trabalhou-se o conteúdo Química Orgânica, na perspectiva Ciência, Tecnologia, Sociedade e Ambiente (CTSA). Para possibilitar a apropriação crítica dos conceitos em Química, foram analisadas as seguintes atividades: aulas expositivas-dialogadas, discussões, pesquisas para exposição oral com os estudantes e questionários. Ao final da SD, o objetivo geral foi atingido por meio dos instrumentos avaliativos propostos e das contribuições dos estudantes durante o processo de ensino-aprendizagem. A avaliação do professor da unidade de ensino mostrou-se satisfatória em relação à SD realizada e ao envolvimento das turmas.
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