Oily sludge derived carbons as peroxymonosulfate activators for removing aqueous organic pollutants: Performances and the key role of carbonyl groups in electron-transfer mechanism

Highlights: • Low-cost carbocatalyst was prepared by one-pot pyrolysis of oily sludge (OS). • OS-derived carbocatalyst was highly efficient to activate peroxymonosulfate. • Carbonyl groups play a key role in electron-transfer nonradical mechanism. • A value-added and reuse approach of OS in water remediation was offered. In this work, low-cost carbon-based materials were developed via a facile one-pot pyrolysis of oily sludge (OS) and used as catalysts to activate peroxymonosulfate (PMS) for removing aqueous recalcitrant pollutants. By adjusting the pyrolysis temperature, the optimized OS-derived carbocatalyst manifested good performance for PMS activation to abate diverse organic pollutants in water treatment. Particularly, an average removal rate of 0.87 mol phenol per mol PMS per hour at a catalyst dosage of 0.2 g L⁻¹ is attained by the OS-derived carbocatalyst, higher than many other documented catalysts. A series of experimental evidences consolidated that organic pollutants were oxidized mainly via electron-transfer mechanism albeit the detection of singlet oxygen (¹O₂) from PMS activation driven by the OS-derived carbocatalyst. Specifically, the proportion of carbonyl groups (CO) in the carbocatalyst adopted with selective modification treatments to tailor the surface chemistry was found to be linearly correlated with the catalytic activity and theoretical calculations demonstrated that the reactions between CO and PMS to form surface reactive complexes were more energetically favorable compared to ¹O₂ generation. Herein, this study not only offers a new strategy for reusing OS as value-added persulfate activators but also deepens the fundamental understanding on the nonradical regime.