Catalytic ozonation of an azo-dye using a natural aluminosilicate

Abstract

Catalytic ozonation of Orange II (100 mg/L) was studied using aluminosilicate Montanit300® (M) modified with H2SO4 (MS) and HCl (MH). Characterization of these samples was performed through several techniques: SEM/EDX, FTIR, XRD, FRX, TPD pyridine, surface area, pHPZC. Acid treatment increased surface area, Si:Al ratio and quantity of acid sites, but reduced pHPZC and Fe and Mn content. Ozonation experiments achieved complete decoloration and remarkable TOC conversions of 66, 65, 88 and 91 % by single ozonation and catalytic ozonation with MH, MS and M, respectively. Higher M and MS activity under acidic pH was attributed to Mn leaching. Decreased mineralization efficiency in the presence of tert-butanol suggested a radical mechanism. At neutral pH, M showed no activity, while MS presented mild activity owing to its enlarged hydrophobicity. The M sample sustained mineralization levels over 20 h. Lower O3 dose caused quick MS deactivation. However, it was reversed through calcination and prevented with a higher oxidant dose. Mn is naturally found in Montanit300®, thus making it an inexpensive catalyst. The development of a dynamic cycle combining reduced and oxidized forms of Mn was key to the outstanding activity observed.