An iron chlorophyll derivative for enhanced degradation of bisphenol A: New insight into the generation mechanism of high-valent iron oxo species

The pressure to environmental concern from toxic precursors of metalloporphyrin synthesis and the inadequate understanding of metalloporphyrin with β-site substituents on activation of peroxides have impeded the full potential of metalloporphyrin for the oxidation of recalcitrant organic compounds. Here, we report a “green” iron(III) chlorophyll derived from naturally abundant chlorophyll. It shows remarkable degradation efficiency of bisphenol A in the presence of hydrogen peroxide, with a second-order rate constant of 87.3 ± 1.1 L·mmol−1·min−1, which is 7-fold faster than the degradation rate of the Fenton oxidation system. It also demonstrates a wide pH tolerance range of 4–12 and is barely affected by concomitant inorganic anions or natural organic matter. Different from the generation of oxygen-centered radicals, including •OH and •O2−, in the Fenton system, a high-valent iron (Ⅳ) -oxo chlorin π-cation radical is formed with an atypical pathway of homolytic O O bond cleavage via a proton-coupled electron transfer process and is responsible for the degradation of bisphenol A, which is confirmed with spectroscopic studies and theoretical analysis. This abundant “green” catalyst could be beneficial for wastewater treatment by addressing the limitation of a narrow acidic pH range and the susceptibility to scavenging of nonselective radicals in conventional Fenton reactions.