Efficient activation of oxone by pyrite for the degradation of propanil: Kinetics and degradation pathway

Highlights: • The pyrite/oxone process was successfully employed for the catalytic degradation of propanil. • Fe(II) regeneration and S conversion effectively enhanced the catalytic activity of pyrite. • SO₄ and OH were the dominant reactive species generated in the pyrite/oxone process. • Activation mechanism of pyrite/oxone process for propanil degradation was interpreted. • A series of intermediates was discovered via four major pathways in the degradation of propanil. Pyrite (FeS₂) is an abundant sulfide-associated iron mineral that exists in the earth. In this study, the pyrite/oxone process was demonstrated to be an effective approach for the catalytic degradation of propanil, where more than 90% decay ([propanil]₀ = 0.01 mM) was achieved within 15 min. Typically, the effects of various experimental parameters, including catalyst loading, oxone dosage, propanil concentration, and initial solution pH, were examined. Two optimal reaction pH values were observed at pH 9.1 and pH 2.9. The generated SO₄ and OH were verified to be the dominant reactive radicals and primarily responsible for the propanil degradation. Both Fe(II) regeneration and sulfur conversion play an important role in oxone activation mechanism and effectively aid the catalytic activity of pyrite. Different co-existing natural water constituents exert dissimilar effects on the pyrite/oxone process. Additionally, the reusability test of pyrite exhibited a reasonable catalytic activity. The pyrite/oxone process was proven efficient in terms of propanil mineralization. A series of reaction intermediates was detected via four major degradation pathways. Overall, the pyrite/oxone process could be a promising approach for the removal of organic compounds in water.