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

Abstract

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.