Novel coagulation waste-based Fe-containing carbonaceous catalyst as peroxymonosulfate activator for pollutants degradation: Role of ROS and electron transfer pathway

Highlights: • A novel Fe-containing carbonaceous catalyst (PMCW) was prepared using hazardous CW • Over 98% of RR2 removal was achieved in the PMCW/PMS system within 10 min reaction. • Both radical and non-radical take effect on RR2 degradation in PMCW/PMS system • Electron transfer induced by −OH and π-π* played a vital role in RR2 degradation • Analyses of QTOF LC/MS and DFT successfully reveal RR2 degradation pathway by PMCW A facile one-step pyrolysis method was employed to prepare an iron containing carbonaceous catalyst using coagulation waste (CW) from paper mill. The catalyst (noted as PMCW) was used to activate peroxymonosulfate (PMS) for decomposition of Reactive Red 2 (RR2). The degradation mechanism was analyzed by reactive oxygen species (ROS) scavenging experiments, electron spin resonance spectroscopy, electrochemical measurements, selective deactivation of the functional groups on the catalyst surface, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results showed that, besides ROS (^• OH, SO₄^{• -} and ¹O₂), electron transfer pathways induced by −OH functional groups and the π-π* system are involved in the degradation mechanism of RR2. Concerning different decomposition pathways, seven intermediates were identified, and three important steps, including attack on the azo group, cleaving the N9−C10 bond, and opening the naphthalene ring, were deduced via application and analysis of quadrupole time-of-flight liquid chromatography/mass spectrometry (QTOF LC/MS) and density functional theory (DFT) calculations based on Fukui indices and electrostatic potential (ESP) distributions. This work not only provides a novel facile recycling strategy of industrial waste from paper manufacturing to good carbonaceous catalysts but also deepens the understanding of the mechanisms of PMS activation with carbonaceous materials.