Publications (4) View all
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Article: Abatement of the inhibitory effect of chloride anions on the photo-Fenton process.
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ABSTRACT: The inhibition of the photo-Fenton (Fe2+/Fe3+, H2O2, UV light) degradation of synthetic phenol wastewater solutions by chloride ions is shown to affect primarily the photochemical step of the process, having only a slight effect on the thermal or Fenton step. Kinetic studies of the reactions of oxoiron (IV) (FeO2+) with phenol indicate that, if FeO2+ is formed in the photo-Fenton degradation, its role is probably minor. Finally, it is shown that, for both a synthetic phenol wastewater and an aqueous extract of Brazilian gasoline, the inhibition of the photo-Fenton degradation of the organic material in the presence of chloride ion can be circumvented by maintaining the pH of the medium at or slightly above 3 throughout the process, even in the presence of significant amounts of added chloride ion (0.5 M).Environmental Science and Technology 01/2008; 41(24):8459-63. · 5.23 Impact Factor -
Article: Preparation of silver nanoprisms using poly(N-vinyl-2-pyrrolidone) as a colloid-stabilizing agent and the effect of silver nanoparticles on the photophysical properties of cationic dyes.
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ABSTRACT: The synthesis of silver nanoprisms in aqueous solution using poly(N-vinyl-2-pyrrolidone) (PVP) with different molecular weights (29, 55 and 1300 kg mol(-1)) as a stabilizing agent is described. Low molecular weight PVP (55 kg mol(-1)) is indicated for the preparation of a stable blue solution containing Ag nanoprisms via extended irradiation of a yellow colloidal solution of nanospheres with polychromatic visible light. The fluorescence properties of some cationic dyes (acridine, 9-aminoacridine, Nile Blue and auramine), free and bound to poly(methacrylic acid), have been studied in the presence of different shaped Ag colloidal particles in solution. Only auramine displays an amplification of the fluorescence signal with increasing colloid concentration, while the fluorescence of the other dyes is quenched by interaction with the polymer-stabilized metal nanoparticles.Photochemical and Photobiological Sciences 10/2003; 2(9):921-5. · 2.58 Impact Factor -
Article: Estudos mecanísticos da origem da inibição da reação foto-fenton por íons cloreto.
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ABSTRACT: O objetivo principal deste estudo foi determinar a origem da inibição do processo foto-Fenton [Fe(II)/Fe(III), 'H IND.2''O IND.2', luz UV] pelo íon cloreto. Um estudo das reações primárias da etapa fotocatalítica do processo foto-Fenton por fotólise por pulso de laser na presença de NaCI mostrou que a inibição reflete: i) fotólise competitiva dos complexos Fé '(CI) POT.2'POSITIVO'' e Fe''(Cl) IND.2'POT.POSITIVO', ii) "captura" do radical hidroxila (dependente do pH) pelo íon cloreto. Esses dois processos formam o ânion radical menos reativo 'CI IND.2 POT.'ponto''NEGATIVO'' em lugar do radical HO, provocando uma progressiva inibição da reação de degradação com a diminuição do pH. Modelagem cinética destes resultados previa que a manutenção do pH em 3,0 durante a fotodegradação evitaria a formação do 'CI IND.2 POT.'ponto''NEGATIVO'', o que foi confirmada através de experimentos de fotodegradação do fenol e da gasolina em meio aquoso na presença de NaCI. Por outro lado, na degradação do fenol pela reação térmica de Fenton [Fe(II)/Fe(III), 'H IND.2''O IND.2'], o radical hidroxila não parece ter um papel muito importante. A degradação térmica não foi inibida pela presença de íon cloreto e a cinética de mineralização do fenol pela reação térmica de Fenton é indistinguível da degradação do fenol pelo processo foto-Fenton inibido por NaCI. Isso sugere que a reação proposta por Hamilton, isto é, a redução de Fe(lIl) a F. Tese (Doutorado). -
Article: Transferência de energia entre corantes catiônicos em sistemas homogêneos
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ABSTRACT: In this work, the energy transfer by dipole-dipole interaction between cationic dyes in n-alcohols (methanol, ethanol, 1-propanol and 1-butanol) is studied by time resolved and steady state fluorescence measurements. The critical radii of energy transfer were determined by three independent methods; the spectral overlap, fluorescence decay profiles, and relative intensity measurements. In all solvents, R0 values of the dye pairs obtained from spectral overlap were between 40 to 90 Å. Steady state and time resolved fluorescence measurements resulted in values of R0 in the range of 50 - 80 Å, with good correlation of values.Química Nova 01/2003; · 0.76 Impact Factor
