Activation of peroxymonosulfate by natural pyrite for effective degradation of 2,4,6-trichlorophenol in water: Efficiency, degradation mechanism and toxicity evaluation

Natural pyrite was employed to activate peroxymonosulfate (PMS) to degrade 2,4,6-trichlorophenol (2,4,6-TCP) in water. The pyrite was proven to be the FeS2 crystal and with the mesopore structure. The optimized system with a ratio of pyrite to PMS at 8:1 showed the highest performance, and more than 99.8% of 2,4,6-TCP was removed by the pyrite/PMS system. Additionally, the removal efficiency of 2,4,6-TCP under various water matrix factors was comprehensively evaluated. Sulfate radical (SO4−) and hydroxyl radical (OH) were identified as the major species that dominated the efficiency of the pyrite/PMS system for organic compound degradation. The static content of SO4− was calculated to be 6.84 × 10−13 mol/L, which was 4.36 times that of OH. The SO4− and OH could powerfully induce the degradation of 2,4,6-TCP by attacking the Cl in the structure with high electron density. According to the Fukui functions calculation, O(9), C(4) and C(1) with higher fr− values were more readily to undergo electrophilic reaction, and the three Cl with higher fr0 values in the structure were easily dechlorinated. The dechlorination, radical substitution, hydroxylation and ring-opening processes caused the degradation of 2,4,6-TCP. Meantime, the dechlorination process significantly decreased the toxicity of the intermediate products. This study proposed an effective and safe process for 2,4,6-TCP degradation.