Ordered mesoporous hematite promoted by magnesium selective leaching as a highly efficient heterogeneous Fenton-like catalyst

Abstract

Ordered mesoporous hematite with an ultrahigh surface area (up to 200 m² g⁻¹) was prepared through a hard templating method of Mg and Fe in mesoporous silica KIT-6 (meso-Mg/Fe₂O₃) and used for highly efficient wet peroxide oxidation of methylene blue. The obtained results showed that approximately two thirds of Mg cations were removed in the leaching process, resulting in a highly porous hematite with a significant amount of defects in the structure. The activated mesoporous iron oxide exhibited excellent catalytic activity for the degradation of methylene blue, achieving above 95% removal of 60 mg L⁻¹ methylene blue after 3 h at reaction conditions of initial pH, 0.6 mg L⁻¹ catalyst and 2600 mg L⁻¹ H₂O₂ dosage. The apparent rate constant of used meso-Mg/Fe₂O₃ is 1.972 h⁻¹, which is 1.22, 3.02 and 4.53 times those of meso-Fe₂O₃, con-Mg/Fe₂O₃ and α-Fe₂O₃, respectively. With the increase of reusability of the meso-Mg/Fe₂O₃ catalyst, both the leaching concentration of Mg and the catalytic activity of the catalyst increased, which is quite different with the catalytic mechanism of composite components in heterogeneous Fenton-like processes, such as Fe–Cu and Fe–Zn composites. The leaching concentrations of iron in the catalysts were found to be low (<5 mg L⁻¹) in consecutive runs. Hence, the meso-Mg/Fe₂O₃ catalyst has proved to be an attractive alternative in the treatment of environmental refractory organic pollutants and has a unique and superb catalytic activity in the heterogeneous Fenton-like system.