Temperature dependence of hydroxyl radical formation in the hv/Fe3+/H2O2 and Fe3+/H2O2 systems

The thermal enhancement of the formation of (OH)-O-. by the hv/Fe(III)/H2O2 system (including the Fe(III)/H2O2 system) was quantitatively investigated with reaction temperatures ranging from 25 to 50degreesC. A temperature dependent kinetic model for the hv/Fe(III)/H2O2 system, incorporating 12 major reactions with no fitted rate constants or activation energies, was developed, and successfully explained the experimental measurements. Particularly, the thermal enhancement of Fe(OH)(2+) photolysis which is the most significant step in the hv/Fe(Ill)/H2O2 system was effectively explained by two factors; (1) the variation of the Fe(OH)(2+) concentration with temperature, and (2) the temperature dependence of the quantum yield for Fe(OH)(2+) photolysis (measured activation energy = 11.4 kJ mol(-1)). Although in both the hv/Fe(III)/H2O2 and Fe(III)/H2O2 Systems, elevated temperatures enhanced the formation of (OH)-O-., the thermal enhancement was much higher in the dark Fe(III)/H2O2 system than the hv/Fe(III)/H2O2 system. Furthermore, it was found that the relative thermal enhancement of the formation of (OH)-O-. in the presence of (OH)-O-. scavengers (tert-butyl alcohol) was magnified in the Fe(III)/H2O2 system but was not in the hv/Fe(III)/H2O2 system. (C) 2004 Elsevier Ltd. All rights reserved.