Kinetic model of photocatalytic oxidation of dye (Orange II) by superoxide radicals

The kinetics of photocatalytic decomposition of dye (Orange II) in the presence of titanium (IV) dioxide was studied. A presented kinetic model takes into account the active forms of particles involved in the process of photocatalytic oxidation. By adding various scavengers, it was found that superoxide radicals (O-2(center dot-)) play the most significant role in dye photodegradation. Tert-butanol (t-BuOH), ammonium oxalate (OA), sodium azide (NaN3), 4-hydroxy-TEMPO (TEMPOL) and dimethyl sulfoxide (DMSO) were used as scavengers with a final concentration of 10 mM of hydroxide radicals (center dot OH), holes (h(+)), singlet oxygen (O-1(2)), superoxide radicals (O-2(center dot-)) and electrons (e(-)) in 40 mL of Orange II solution. The proposed kinetic model includes the following stages: photogeneration of particles, formation of superoxide radicals and their interaction with organic dye, products and inactive surfaces. Studies were conducted to determine the kinetic parameters of the reaction, particularly the order of Orange II photodegradation, showed that the reaction follows a pseudo-first-order kinetics, which is consistent with the proposed kinetic model. The resulting linear dependence of ln(C-0/C) with time shows that the photodecomposition reaction of Orange II is a pseudo-first order reaction, the rate constant of which is (35.1 +/- 1.3)center dot 10(-3) min(-1).