B-doped NiFe2Ox based on the activation of peroxymonosulfate for degrading 2,4-dichlorophenoxyacetic acid in water

Catalysts used to degrade pollutants are easily limited by surface reaction sites. Herein, we modified the catalyst by doping boron (B) to overcome the above shortcomings. B-doped NiFe2Ox catalysts with oxygen vacancies (OVs) were synthesized by the sol–gel method to activate peroxymonosulfate (PMS) for 2,4-dichlorophenoxyacetic acid (2,4-D) degradation. 2,4-D is a widely used herbicide in agricultural production. However, it was difficult to be degraded and dangerous to human health. The B-doped NiFe2Ox (especially 10B-NiFe2Ox) exhibited a high catalytic capacity for 2,4-D, aceclofenac (ACF), bisphenol S (BPS) and amidotrizoic acid (DTZ). And the removal rate of 2,4-D in 10B-NiFe2Ox/PMS system was increased by 26.4 percentage points compared with NiFe2O4/PMS system. It was verified that B-O-Fe and B-O-Ni were formed. And OVs were formed on the surface of the catalyst after B doping. SO4− was confirmed as the major reactive oxygen species (ROS) by quenching experiments. Metal sites and OVs were conducive to the generation of SO4−. According to the in situ analysis of the interfacial reaction mechanism, the –OH structure of HSO5− and H2O could be adsorbed on the OVs sites and combined with the adjacent Lewis acid sites. The cycle of Fe2+/Fe3+ and Ni2+/Ni3+ promoted the interfacial electron transfer of the combined HSO5−, and thus generating SO4−. The degradation pathways of 2,4-D were proposed through its intermediates and density functional theory (DFT) calculation by the Fukui function. The degradation mechanism included decarboxylation, dechlorination, dehydroxylation, hydroxylation, H-abstraction, bond cleavage and ring opening. This study verified the possibility of highly efficient pollutant degradation by activating PMS with B-doped modified catalyst.