Kinetic, mechanistic, and thermodynamic investigations on ferrofluid-catalyzed oxidation of L-ascorbic acid by hydrogen peroxide in acidic aqueous solution

The reduction of ferrofluid (FF) by L-ascorbic acid (H₂A) and the reoxidation of the reduced FF to its original form by hydrogen peroxide have been investigated in aqueous acidic medium. The rate of reduction of FF was found to be first order with respect to [H₂A] and [FF] and independent with respect to [H₂O₂] and ionic strength. The rate of reduction of FF increased with increasing pH (2.5-4.0), having an inverse first order dependence in [H⁺]. With increasing temperature (15-45°C), the rate of reduction was increased in line with the Arrhenius equation. Based on experimental evidence and results a mechanism, operative to reduce FF and reoxidize the reduced FF by H₂O₂, which makes the system catalytic, is suggested. Thermodynamic quantities associated with FF-catalyzed oxidation of H₂A by H₂O₂ were determined and compared with other closely related systems.