A comparative study of spinel structured Mn₃O₄, Co₃O₄ and Fe₃O₄ nanoparticles in catalytic oxidation of phenolic contaminants in aqueous solutions

Spinel structured Mn₃O₄, Co₃O₄ and Fe₃O₄ nanoparticles were prepared, characterized, and tested in degradation of aqueous phenol in the presence of peroxymonosulfate. It was found that Mn₃O₄ and Co₃O₄ nanoparticles are highly effective in heterogeneous activation of peroxymonosulfate to produce sulfate radicals for phenol degradation. The activity shows an order of Mn₃O₄>Co₃O₄>Fe₃O₄. Mn₃O₄ could fast and completely remove phenol in about 20min, at the conditions of 25ppm phenol, 0.4g/L catalyst, 2g/L oxone®, and 25°C. A pseudo first order model would fit to phenol degradation kinetics and activation energies on Mn₃O₄ and Co₃O₄ were obtained as 38.5 and 66.2kJ/mol, respectively. In addition, Mn₃O₄ exhibited excellent catalytic stability in several runs, demonstrating that Mn₃O₄ is a promising catalyst alternative to toxic Co₃O₄ for water treatment.