In meeting the need for environmental remediation in wastewater treatment and the development of popular sulfate-radical-based advanced oxidation processes (SR-AOPs), a series of Co/Fe-based catalysts with confirmed phase structure were prepared through extended soft chemical solution processes followed by atmosphere-dependent calcination. Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and ⁵⁷Fe Mössbauer spectroscopy were employed to characterize the composition, morphology, crystal structure and chemical state of the prepared catalysts. It was shown that calcination in air, nitrogen and ammonia atmospheres generated Co-Fe catalysts with cobalt ferrite (CoFe₂O₄), Co-Fe alloy and Co-Fe nitride as dominant phases, respectively. The prepared Co/Fe-based catalysts were demonstrated to be highly efficient in activating peroxymonosulfate (PMS) for organic Orange II degradation. The activation efficiency of the different catalysts was found to increase in the order CoFe₂O₄ < Co-Fe nitride < Co-Fe alloy. Sulfate radical was found to be the primary active intermediate species contributing to the dye degradation for all the participating catalysts. Furthermore, a possible reaction mechanism was proposed for each of the studied catalysts. This study achieves progress in efficient cobalt-iron catalysts using in the field of SR-AOPs, with potential applications in environment remediation.

Nanocrystalline EuCrO₃ particles (∼25 nm) have been prepared by pre-milling a 1 : 1 molar mixture of Eu₂O₃ and Cr₂O₃ for 60 h followed by sintering at 700 °C (12 h). This temperature is ∼500–600 °C lower than those at which the material, in bulk form, is conventionally prepared. Rietveld analysis of the x-ray powder diffraction pattern of the EuCrO₃ nanoparticles favours a structural model involving a slight degree of cationic exchange where ∼11% of the Eu³⁺ and Cr³⁺ ions exchange their normal dodecahedral A- and octahedral B-sites, respectively, in the perovskite-related structure. This cationic site exchange, which is unusual in a perovskite structure, has been well supported by the corresponding room-temperature ¹⁵¹Eu Mössbauer spectrum of the nanoparticles that in addition to displaying a distribution in the principal component of the EFG tensor (V _zz ) at the usual A-sites of the ¹⁵¹Eu nuclei, also revealed the presence of a subcomponent with ∼11% area fraction and a considerably increased |V _zz | value that was associated with Eu³⁺ ions at octahedral B-sites. X-ray photoelectron and Auger electron spectroscopic techniques reveal a complex surface structure where extremely thin layers of un-reacted Eu₂O₃ and Cr₂O₃ cover most of the EuCrO₃ nanoparticles' surfaces together with some traces of elemental Cr. The binding energies associated with Eu³⁺ 3d_5/2, Eu³⁺ 4d_3/2, Cr³⁺ 2p_3/2 and O²⁻ 1s core-level electrons in EuCrO₃ are estimated from the x-ray photoelectron data for the first time.