[Degradation of RBK5 by High Crystallinity Mn-Fe LDH Catalyst Activating Peroxymonosulfate].

Abstract

High crystallinity Mn-Fe LDH was synthesized by improved co-precipitation combined with the hydrothermal method and was utilized as a catalyst for peroxymonosulfate (PMS) activation to degrade reactive black 5. The high crystal purity and clear lamellar structure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The operating parameters such as Mn/Fe molar ratio, catalyst dosage, PMS concentration, and initial pH value on the absorption efficiency, catalytic degradation, and reaction kinetics of RBK5 were also investigated. The results demonstrated that high crystallinity Mn-Fe LDH has good adsorption capacity and high catalytic efficiency. The degradation efficiency of RBK5 (20 mg·L^-1) could reach 86% within 90 min when the Mn/Fe molar ratio was 1, the catalyst dosage was 0.2 g·L^-1, the PMS concentration was 1 mmol·L^-1, and the initial pH value was 7.0. The reaction process follows pseudo-first-order reaction kinetics (R²>0.9). In addition, the quenching experiment indicated that SO₄^-·and·OH were the main active species that degraded RBK5 from the Mn-Fe LDH/PMS system. The XPS analysis of the catalyst before and after the reaction confirmed the synergistic effect between Mn and Fe. The charge balance between Mn(Ⅱ) and Fe(Ⅲ) on the LDH surface and CO₃^2- in layers stabilized the structure, thus promoting the synergistic effect of Mn and Fe on the lamellar surface and improving the activation efficiency of PMS by Mn-Fe LDH. Three-dimensional fluorescence and the UV-Vis scanning spectral analysis were preliminarily discussed to understand the degradation process of RBK5.