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Water/Silica Nanoparticle Interfacial Kinetics of Sulfate, Hydrogen Phosphate, and Dithiocyanate Radicals

Authors

  • Paula Caregnato,

    1. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
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  • Sonia G. Bertolotti,

    1. Departamento Química Física, Universidad Nacional de Río Cuarto, Río Cuarto, Argentina
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  • Mónica C. Gonzalez,

    1. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
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  • Daniel O. Mártire

    Corresponding author
    1. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, La Plata, Argentina
      *To whom correspondence should be addressed: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Chemical Kinetics and Photochemistry, Casilla de Correo 16, Sucursal 4, La Plata, Buenos Aires 1900, Argentina. Fax: 54 221 425 4642; e-mail: dmartire@inifta.unlp.edu.ar
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*To whom correspondence should be addressed: Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Chemical Kinetics and Photochemistry, Casilla de Correo 16, Sucursal 4, La Plata, Buenos Aires 1900, Argentina. Fax: 54 221 425 4642; e-mail: dmartire@inifta.unlp.edu.ar

ABSTRACT

The values of the rate constants for the reactions of the sulfate (2.5 × 109M−1 s−1) and hydrogen phosphate (2.2 × 108M−1 s−1) radicals with silica nanoparticles are obtained by flash photolysis experiments with silica suspensions containing S2O82− or P2O24−, respectively. The interaction of these radicals with the silica nanoparticles leads to formation of transients, probably adsorbed sulfate and hydrogen phosphate radicals, with absorption maxima at around 320 and 350 nm, respectively. A different mechanism takes place for the interaction of the less oxidizing dithiocyanate radicals with the silica nanoparticles. These radicals selectively react with the dissociated silanol groups of the nanoparticles with a rate constant at 298.2K of 7 × 107M−1 s−1 (per mol of SiO groups), and there is no evidence for their adsorption at the surface. All the results are discussed in terms of the Smoluchowski equation and redox potential of the inorganic radicals.

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