Metal ferrites nanocrystallites, MFe2O4 (M = Mn, Co, Ni, Zn) were prepared by coprecipitation method and characterized by a combination of physico‐chemical and spectroscopic techniques. MFe2O4 nanoparticles having particle size in the range 10–35 nm were tested as catalysts in the oxidation of o‐phenylenediamine (OPD) to 2,3–diaminophenazine (DAP) using hydrogen peroxide as oxidant at room temperature. Kinetic data was collected for the catalytic oxidation of OPD to DAP by monitoring the UV–vis absorbance at 415 nm and fit well to the Michaelis–Menten model yielding kinetic parameters Km (Michaelis–Menten constant) and Vmax (maximum rate of reaction). MnFe2O4 nanoparticles provide the highest catalytic activity in the oxidation of OPD to DAP at room temperature. A colorimetric method was developed based on the MnFe2O4/OPD system for the detection of H2O2 in reaction solution. The method has a detection limit of 30 μM for H2O2 and wide linear range.

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