Niobian iron oxides as heterogeneous Fenton catalysts for environmental remediation

Heterogeneous Fenton or Fenton-like reagents consist of a mixture of an iron-containing solid matrix and a liquid medium with H₂O₂. The Fenton system is based on the reaction between Fe^2?+? and H₂O₂ to produce highly reactive intermediate hydroxyl radicals (^???OH), which are able to oxidize organic contaminants, whereas the Fenton-like reaction is based on the reaction between Fe^3?+? and H₂O₂. These heterogeneous systems offer several advantages over their homogeneous counterparts, such as no sludge formation, operation at near-neutral pH and the possibility of recycling the iron promoter. Some doping transition cations in the iron oxide structure are believed to enhance the catalytic efficiency for the oxidation of organic substrates in water. In this work, goethites synthesized in presence of niobium served as precursors for the preparation of magnetites (niobian magnetites) via chemical reduction with hydrogen at 400°C. These materials were used as Fenton-like catalysts. Both groups of (Nb, Fe)-oxide samples were characterized by ⁵⁷Fe Mössbauer spectroscopy at 298 K. The results show that increasing niobium contents raise the catalytic potential for decomposition of methylene blue, which was, in this work, used as a model molecule for organic substrates in water.