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

The influence of the iron precursor salt on the preparation of Carbon-Fe catalysts was evaluated based on the generation of (OH)-O-center dot 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 N-2 physisorption, X-ray diffraction, scanning electron microscopy and spectroscopic techniques (FTIR, EDX, XPS); these properties were related to the (OH)-O-center dot 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-ACAFe, 1.5 for C-AC-SFe and 1.7 for C-AC-NFe, which is related to the (OH)-O-center dot generated: 53.8 mu M g(-1), 37.9 mu M g(-1) and 42.4 mu M g(-1), respectively. The (OH)-O-center dot 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)-O-center dot. In the case of C-AC-NFe, Fe was fixed within the texture of the carbon and the (OH)-O-center dot 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.