Boron as a promoter in the goethite (α-FeOOH) phase: Organic compound degradation by Fenton reaction

Abstract

The aim of this study was to obtain iron oxides (goethite phase, α-FeOOH) to be used as Fenton catalysts in the catalytic oxidation of methylene blue (MB). Moreover surface modifications were attempted by treating the oxides with boric acid in order to improve the materials’ catalytic properties through the generation of more active groups on the surface of goethite. The types of structures formed on the surface were investigated through the following characterization techniques: vibrational infrared spectroscopy, Mössbauer spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy and BET surface area measurements. The results of these characterization analyses the showed complexation of boric acid on the surface of goethites and the partial reduction of some Fe(III) to Fe(II) species, resulting of a hybrid material containing both goethite and magnetite phases. When tested in the oxidation of organic compounds, the new class of iron oxide showed high capacity for degradation of organic compounds present in the solution. The Gt-B catalyst exhibited enhanced catalytic activity in degradation of methylene blue compared with the pure goethite, especially Gt-B1×4 which, after 240min of reaction, was able to degrade about 80% of the MB in solution. The increase in the catalytic activity was assigned to the role of boron as a promoter in the transfer of electrons from iron to hydrogen peroxide, the increasing of surface area and the presence of Fe(II) species, which are kinetically more favourable for the Fenton’s reaction. In addition, theoretical calculations were carried out at the density functional theory (DFT) level in order to investigate the interaction between goethite and boric acid. The theoretical findings showed that the treatment with the H3BO3 significantly modifies the electron density of goethite (100).