Photocatalytic wet peroxide oxidation process at circumneutral pH using ilmenite as catalyst

Abstract

The effect of the initial pH upon Catalytic Wet Peroxide Oxidation (CWPO) and CWPO-Photoassisted (λ: 200–600 nm) has been evaluated with ilmenite (FeTiO3) as catalyst (450 mg/L) and phenol as target compound (100 mg/L). Under dark conditions, pH0 plays a key role on the mineralization degree that steeply decreased (from 50% to almost negligible) as the pH0 value rose (from 3 to 6, respectively) entailing that HO generation occurs following the classical Fenton mechanism. The irradiation with UV–vis light allows to overcome this pH-dependence, increasing the organic matter conversion above 95% within the pH range 3–6. This can be explained by considering, on the one hand, the photocatalytic properties of ilmenite, provoking H2O2 decomposition into HO radicals and, on the other hand, the effect of UV–vis light upon Fe(II)-Fe(III) cycle increasing the H2O2 decomposition rate and, consequently, HO generation at acidic pH. Therefore, under these conditions H2O2 decomposition occurs following two different mechanisms: the classical Fenton one at acidic pH and by photogenerated charges at circumneutral one. A lumped kinetic model is proposed to predict the evolution of TOC upon CWPO-Photoassisted process. Finally, ilmenite stability has been evaluated through several sequential runs.