On disclosing the role of mesoporous alumina in the ozonation of sulfamethoxazole: Adsorption vs. Catalysis

Abstract

Ordered mesoporous alumina (MA) and Fe-doped MA were synthesized by evaporation-induced self-assembly and tested for the ozonation of sulfamethoxazole (SMX). The synthesis methodology produced MA whose surface and structural properties exceeded those of commercial types displaying a BET surface area of 263 m2/g, a pore volume of 0.8 cm3/g and aligned cylindrical pores of c.a. 10 nm. The ozonation of SMX (20 mg/L) was performed in a semibatch stirred tank reactor at: T = 22 °C, [O3]gas = 10 mg/L, Qgas = 42 L/h NTP, [solid] ≈ 1 g/L, t = 120 min. Single ozonation achieved fast and complete SMX removal and mineralized up to 35% of the organics at neutral pH. The addition of MA or Fe-doped MA did not affect the removal rate of SMX, but did achieve a remarkable TOC removal up to 86% at acid pH. However, under the selected operating conditions, ferric species did not improve the removal of organic matter. Then, the adsorption and catalytic contribution of MA was evaluated in specifically-designed experiments. While SMX adsorption was low, its oxidation intermediates did adsorb onto MA surface. Despite the high ability of the materials to decompose ozone, the results revealed that the by-products adsorption is the prevailing process for the TOC removal. After four successive reuses, MA reduced its adsorption performance due to chemisorption of carboxylates. Nevertheless, the worn material was regenerated by direct ozonation in gas phase. In addition, primary transformation products were identified by LC–ESI–TOF–MS and the scavenging effect of the water matrix was assessed using bottled water and a real secondary wastewater.