Enhanced oxidative degradation of 2,4-dichlorophenol by iron oxychloride supported on graphitic carbon nitride via peroxymonosulfate activation: Significant role of Fe(II)/Fe(III) conversion cycle.

The activation of peroxymonosulfate (PMS) by heterogeneous catalysts presents an exciting but challenging strategy for degrading persistent organic pollutants in water. Iron oxychloride (FeOCl) is considered a promising heterogeneous catalyst due to its unique oxygen bridge structure, which could render it more active by facilitating the iron valence transitions between Fe(II) and Fe(III). However, the limited Fe(II)/Fe(III) conversion cycle rate hinders its catalytic activity, leading to unsatisfactory PMS activations in practical applications. Herein, we demonstrated the performance and the mechanistic pathway of enhanced FeOCl (CNFeOCl) catalytic activation using a graphitic carbon nitride (g-C3N4) with a unique electronic structure as a carrier employing 2,4-dichlorophenol (2,4-DCP) as a representative pollutant. The CNFeOCl/PMS system achieved complete degradation of 2,4-DCP (30 mg/L) in a short time (<5 min), whereas the FeOCl/PMS system degraded only 35.98% under the same conditions. The high 2,4-DCP degradation rate of CNFeOCl was due to its improved Fe(II)/Fe(III) ratio (34.34%/40.03%), increased specific surface area (30.32 m2/g), and reduced charge-transfer resistance. Combining a series of characterizations, electron spin resonance (ESR) detection, and quenching experiments, the investigations elucidated the enhanced catalytic activation mechanism of CNFeOCl which includes dominant reactive oxygen species (ROS) generation and some key factors that generally affected the efficiency of oxidative degradation. We believe this study offers new insights into the intrinsic role of g-C3N4 supported FeOCl for PMS activation and provides theoretical support to guide the rational design for developing efficient iron-based catalysts toward heterogeneous catalysis.