Ultrasound-assisted heterogeneous activation of peroxymonosulphate by natural pyrite for 2,4-diclorophenol degradation in water: Synergistic effects, pathway and mechanism

In this paper, the natural pyrite was firstly used as peroxymonosulphate (PMS) activator in conjunction with ultrasonic irradiation (US) for 2,4-dichlorophenol (2,4-DCP) degradation in water. The most relevant findings indicated that a superior degradation of 2,4-DCP has been successfully achieved in pyrite/PMS/US system compared with pyrite/PMS and/or pyrite/US systems, which involved a synergistic effect between sonolysis and Fenton-like reaction. Within 120 min, nearly 98% of 2,4-DCP could be degraded at optimum reaction conditions of pyrite 1.00 g L⁻¹, 2,4-DCP 10 mg L⁻¹, PMS 2.00 mM and pH 4.02. A significantly enhanced PMS decomposition was probably ascribed to the sonochemistry (PMS/US and pyrite/US systems) and catalytic chemistry (pyrite/PMS system) under acidic conditions. Both SO₄ ^[rad]− and HO^[rad] took part in reaction process, while the SO₄ ^[rad]− was dominant for 2,4-DCP degradation. A total of six intermediate products including 3,5-dichlorocatechol, 2-chlorophenol, 4-chlorocatechol, hydroquinone, maleic acid and oxalic acid were identified using GC/MS analyses to clarify the possible degradation pathways, which involved hydroxylation and substitution reactions. Compared to other Fenton reaction systems, both maximum degradation and mineralization levels of 2,4-DCP have been obtained from pyrite/PMS/US system. This study provides an interesting insight for PMS activation by the natural mineral-based catalyst with US irradiation for in situ organic pollutants remediation.