Water/ silica nanoparticles interfacial kinetics of sulfate, hydrogen phosphate and dithiocyanate radicals.

PAULA CAREGNATO; SONIA G. BERTOLOTTI; MÓNICA C. GONZALEZ; DANIEL O. MÁRTIRE

PHOTOCHEMISTRY AND PHOTOBIOLOGY

American Society for Photobiology

Lugar: Lawrence, USA; Año: 2005 vol. 81 p. 1526 - 1533

0031-8655

The values of the rate constants for the reactions of the sulfate (2.5 x 109 M-1s-1) and hydrogen phosphate (2.2 x 108 M-1s-1) radicals with silica nanoparticles are obtained by flash-photolysis experiments with silica suspensions containing S2O82- or P2O84-, 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 298.2 K of  7 x 107 M-1s-1 (per mole 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. winDirVariable="C:/WINDOWS"