Unraveling the critical role of iron-enriched sludge hydrochar in mediating the Fenton-like oxidation of triclosan

Abstract

The traditional Fenton system is subject to the low efficiency of the Fe(III)/Fe(II) conversion cycle, with significant attempts made to improve the oxidation efficiency by overcoming this hurdle. In support of this goal, iron-enriched sludge-derived hydrochar was prepared as a high-efficiency catalyst by one-step hydrothermal carbonization and its performance and mechanisms in mediating the oxidation of triclosan were explored in the present study. The hydrochar prepared at 240 °C for 4 h (HC_240-4) had the highest removal of triclosan (97.0%). The removal of triclosan in the HC_240-4/H₂O₂ system was greater than 90% in both acidic and near-neutral environments and remained as high as 83.5% after three cycles, indicating the broad pH applicability and great recycling stability of sludge-derived hydrochar in Fenton-like systems. H₂O₂ was activated by both persistent free radicals (PFRs; 19.7%) and iron (80.3%). The binding of Fe(III) to carboxyl decreased the electron transfer energy from H₂O₂ to Fe(III), making its degradation efficiency 2.6 times greater than that of the conventional Fenton reaction. The study provides a way for iron-enriched sludge utilization and reveals a role for hydrochar in promoting iron cycling and electron transfer in the Fenton reaction.

Keywords: Electron transfer; Fenton-like system; Hydrochar; Iron-enriched sludge; Triclosan.