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

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) had the highest removal of triclosan (97.0%). The removal of triclosan in the HC/HO 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. HO 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 HO 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.