A Kinetic Study of the Reactions of Sulfate Radicals at the Silica Nanoparticle-Water

PAULA CAREGNATO; VERóNICA C. MORA; GALO CARRILLO LE ROUX; DANIEL O. MáRTIRE; MóNICA C. GONZALEZ

JOURNAL OF PHYSICAL CHEMISTRY B

American Chemical Society

Lugar: Washington D.C. , USA.; Año: 2003 vol. 107 p. 6131 - 6138

1089-5647

Sulfate radicals, SO4.-, were generated by flash photolysis of aqueous S2O82- solutions and the reactions of the inorganic radicals with the surface of suspended silica nanoparticles (NP) investigated. In the presence of colloidal silica no absorption traces due to SO4.- radicals are observed at 100 ìs after the flash of light. However, two transient species with absorption maxima around 320 nm and 600 nm, respectively, are formed. A kinetic analysis of the experimental results indicate that SO4.-radicals are “adsorbed” on the NP surface, leading to the formation of an adduct, with lambda max. ~ 330 nm (epsilon ~ 7000 cm-1 M-1) and showing similar reactivity to that observed for the sulfate radical in aqueous solutions. NP - sulfate radical adducts react with adsorbed water and with single and geminal SiO- sites with reaction rate constants of 1.5 x 1014 x e-(58±12)kJ/mol)/RT s-1, < 103 x e-(2±17)kJ/mol/RT s-1 and < 1011 x e-(46±13)kJ/mol/RT s-1, respectively. Two different SiO. surface defects, showing similar spectra (lambda max. ~ 600 nm) but different reactivities, are formed from the reaction of NP-sulfate radicals and deprotonated geminal and single silanols.   winDirVariable="C:/WINDOWS"