In-situ constructed NiCoFe-sulfide porous cube-like structure enable photo-synergistic PMS activation for efficient levofloxacin degradation

Accelerating the Mⁿ⁺/Mⁿ⁺¹ redox cycling and enhancing electron-transfer efficiency during peroxymonosulfate (PMS) activation remain major challenges in advanced oxidation processes. In this work, a trimetallic nickel-cobalt-iron Prussian blue analogue (NiCoFe-PBA) precursor was synthesized via a co-precipitation method, followed by calcination and subsequent hydrothermal sulphuration, yielding a catalyst capable of photo-synergistic PMS activation for the degradation of levofloxacin (LEV). Oxygen vacancies were generated through the partial removal of lattice oxygen during air calcination and were further enriched by sulfur ion incorporation via hydrothermal sulfidation, which induces anion exchange and lattice distortion. Structural characterizations and catalytic experiments consistently confirm that NiCoFe-PBA-O-S possesses a markedly increased oxygen-vacancy density. Notably, the combined effects of sulfur species, Ni incorporation, and visible-light excitation markedly facilitated Fe³⁺/Fe²⁺ and Co³⁺/Co²⁺ redox cycling by enhancing interfacial electron transfer, enabling efficient photo-synergistic PMS activation. Consequently, 100% LEV removal was achieved within 30 min, with a high degradation rate constant of 0.46 min⁻¹, surpassing most reported catalysts. More importantly, the catalyst retained over 80% LEV removal efficiency within 30 min after eight reuse cycles, and after sulfur regeneration, the 30 min removal efficiency recovered to above 90%. Mechanistic investigations demonstrated that the degradation process was predominantly governed by reactive species in the order O₂•^- > ¹O₂ > SO₄•^- > •OH. This work provides a generalizable strategy for designing recyclable, high-efficiency heterogeneous catalysts for wastewater treatment applications.