Heterogeneous activation of peroxymonosulfate by Co-doped Fe₂O₃ nanospheres for degradation of p-hydroxybenzoic acid

Environmental remediation has become more effective when using nanotechnologies. In this study, iron oxide (α-Fe₂O₃) nanospheres with different cobalt doping levels (xCo-Fe₂O₃) were synthesised and applied in the heterogeneous activation of peroxymonosulfate (PMS) for the degradation of p-hydroxybenzoic acid (p-HBA). The catalyst (3Co-Fe₂O₃) with 3% Co doping exhibits the best performance for PMS activation, possibly because of the larger specific surface area and the tailored catalyst surface as confirmed by X-ray photoelectron spectroscopy (XPS). Reaction parameters were investigated to optimise the degradation efficiency. The metal ions leaching tests confirmed the higher stability of the catalyst, thanks to the leaching suppression by the doping of Co²⁺. The main contribution of free radicals (SO₄^•- and ^•OH) was confirmed by electron paramagnetic resonance (EPR) spectra, whereas partial contribution of oxygen anions and singlet oxygen (O₂^•-, ¹O₂) was observed during the quenching tests. Finally, a radical based degradation mechanism was proposed for the removal of p-HBA. It is expected to open up a novel perspective for the application of iron oxide as a potential catalyst for the removal of emerging contaminants.