Biomass-derived pyrolytic carbons accelerated Fe(III)/Fe(II) redox cycle for persulfate activation: Pyrolysis temperature-depended performance and mechanisms

• Pyrolytic carbon exhibited excellent catalytic activity in Fe 3+ /PS system. • PC400 could significantly and continuously accelerate Fe 3+ /Fe 2+ circulation. • Fe(IV) and surface electron-transfer were identified as main nonradical pathways. • Appreciable SMX removal was obtained in the real water matrixes. The oxidation efficiency of iron/persulfate coupled system was limited by the sluggish Fe 3+ /Fe 2+ cycle and severe Fe 3+ precipitation. In this study, we reported that pyrolytic carbon under low-temperature (PC400) could significantly and continuously accelerate the Fe 3+ /Fe 2+ circulation in the Fe 3+ -mediated persulfate system. The fast Fe 3+ /Fe 2+ circulation was due to the transformation between semiquinone radicals and quinones on PC400, resulting in the great reusability and continuous degradation of sulfamethoxazole (SMX). In contrast, pyrolytic carbon derived under high temperature (PC700) could not maintain the Fe 3+ /Fe 2+ cycle for continuous SMX degradation. SMX removal in both two systems was barely affected by the presence of chloride and humic acid. Even in the real water matrixes (e.g., seawater, piggery wastewater, and landfill leachate), appreciable SMX removal was obtained because of the nonradical reaction pathways, including high-valence Fe(IV) and surface electron-transfer process, verified by methyl phenyl sulfoxide-based probe tests, Mössbauer spectroscopy, electrochemical test, and kinetic calculation. This study advances the knowledge of Fe 3+ -mediated persulfate reaction enhanced by pyrolytic carbons. The outcomes will inspire new strategies for developing cost-effective and efficient carbon-accelerated Fenton-like systems.