A combined theoretical and experimental study on the oxidation of fulvic acid by the sulfate radical anion

P.M. DAVID GARA; G.N. BOSIO; MÓNICA C. GONZÁLEZ; NINO RUSSO; MARIA C MICHELINI; REINALDO PIS DIEZ; DANIEL O. MÁRTIRE

Photochem. Photobiol. Sci.

RSC

Año: 2009 vol. 8 p. 992 - 997

The kinetics of the reaction of sulfate radicals with the IHSS Waskish peat fulvic acid in water wasinvestigated in the temperature range from 289.2 to 305.2 K. The proposed mechanism considers thereversible binding of the sulfate radicals by the fulvic acid. The kinetic analysis of the data allows thedetermination of the thermodynamic parameters DG◦ = -10.2 kcal mol-1, DH◦ = -16 kcal mol-1 andDS◦ = -20.3 cal K-1 mol-1 for the reversible association at 298.2 K. Theoretical (DFT) calculationsperformed with the Buffle model of the fulvic acids support the formation of H-bonded adductsbetween the inorganic radicals and the humic substances. The experimental enthalpy change compareswell with the theoretical values found for some of the investigated adducts.