Oxygen-vacancy-rich N-doped NiFe₂O₄ activates peroxymonosulfate for efficient water purification

An efficient catalyst with abundant oxygen vacancies (OVs) was obtained via nitrogen (N) doping NiFe₂O₄ for peroxymonosulfate (PMS) activation to achieve durable water purification. The N-NiFe₂O₄ activated process enhanced the formation of SO₄^[rad]− and ·OH, thus endowing the system with high decontamination performance compared to pristine NiFe₂O₄. The influence of complex aquatic matrices on the N-NiFe₂O₄/PMS system towards 2,4-dichlorophenoxyacetic acid (2,4-D) removal was investigated in detail. The systematic evaluation revealed that the 5.0 % N-doped NiFe₂O₄/PMS system demonstrated optimal catalytic activity, achieving an 86.9 % removal efficiency of 2,4-D within 15 min. Radical quenching experiments identified SO₄^[rad]− and ·OH were predominantly responsible for 2,4-D degradation. According to the in situ tests and Density functional theory (DFT) calculation, the constructed OVs on N-NiFe₂O₄ greatly promoted the adsorption of PMS, and next served as reactive sites for electron transfer via the Fe³⁺ or Ni²⁺ sites, which further activated PMS for the formation of SO₄^[rad]−. In short, this work gives an effective strategy to prepare high-performance catalysts for durable water purification system construction.