Modeling Fe(II)/Fe(III) Redox Cycle in the Presence of Dihydroxybenzenes and Peroxymonosulfate

Activation of peroxymonosulfate (PMS) by iron species represents an efficient advanced oxidation route for the degradation of contaminants in water, being Fe(III) reduction a crucial stage. In this work, the role of protocatechuic acid (pCtchA) in the Fe(II)/Fe(III)/PMS system was investigated through a mechanistic model constructed from a comprehensive set of elementary reactions describing radical and nonradical pathways. Model simulations were validated with batch reactor data and accurately reproduced the effects of iron (2.0 × 10−6−2.0 × 10−5 M) and PMS (4.1 × 10−5−2.45 × 10−3 M) concentrations, temperature (10–50ºC), and pH (2–7). The results confirm that Fe(III) reduction to Fe(II) is the rate-determining step. Optimal degradation occurs near pH 3.5, where Fe(III)–pCtchA monocomplexes predominate. Proton concentration is inversely proportional to the efficacy of the process in the acidic region. The apparent activation energy for Fe(III) reduction is approximately 36 kJ mol−1. This study provides a quantitative kinetic framework for the Fe(II)/Fe(III)/PMS system accounting for the effect of essential parameters such as pH, reagent concentrations, and temperature, demonstrating its potential as a sustainable catalytic process in aqueous media.