Iron precursor salt effect on the generation of [rad]OH radicals and sulfamethoxazole degradation through a heterogeneous Fenton process using Carbon-Fe catalysts

Abstract

The influence of the iron precursor salt on the preparation of Carbon-Fe catalysts was evaluated based on the generation of OH radicals in a heterogeneous Fenton process applied to the degradation of sulfamethoxazole (SMX). Carbon catalysts were obtained with 9% Fe by weight using three iron salts: iron acetate (C-AC-AFe), iron sulfate (C-AC-SFe) and iron nitrate (C-AC-NFe). Characterization of catalysts was evaluated by N2 physisorption, X-ray diffraction, scanning electron microscopy and spectroscopic techniques (FTIR, EDX, XPS); these properties were related to the OH generation kinetics and to SMX degradation rate. The iron precursor salt favors the anchoring of the metal in different oxidation state on the catalyst in a proportion of: Fe2+ / Fe3+ = 4.1 for C-AC-AFe, 1.5 for C-AC-SFe and 1.7 for C-AC-NFe, which is related to the OH generated: 53.8 μM g−1, 37.9 μM g−1 and 42.4 μM g−1, respectively. The OH generation kinetics were described by a pseudo-first-order model with rate constants of 0.0252 and 0.0299 min−1 for C-AC-AFe and C-AC-SFe respectively, which coincide with the kinetic constants for the degradation of SMX (0.0262 and 0.0297 min−1), therefore, the oxidation process is carried out by OH. In the case of C-AC-NFe, Fe was fixed within the texture of the carbon and the OH generation was the lowest (0.0005 min−1), explaining the reaction is limited by diffusion. For SMX, the degradation percentage achieved for 20 mg L−1 was: 98.2 % in 120 min for C-AC-AFe, 98.1 % in 180 min for C-AC-SFe and 92.8 % in 210 min for C-AC-NFe.