Construction of biomass-derived magnetic-recyclable FeNi-LDO@CS to activate persulfate for simultaneous degradation of cationic and anionic dyes: Discrepancy, mechanism and toxicity analysis

Abstract

In this study, layered chitosan-based magnetic nickel ferrite NiFe₂O₄/chitosan (CS-LDO) composites were synthesized. The results show that under optimal conditions, 98 % of methylene blue (MB) and 92 % of xylenol orange (XO) can be simultaneously degraded within 120 min in the CS-LDO/persulfate (PS) system, and the removal rates of total organic carbon (TOC) and chemical oxygen demand (COD) can reach 67.32 % and 74.23 %, respectively. In addition, the strong magnetism of the material itself and multiple cycle experiments indicate that CS-LDO has good recyclability and reusability. The results of quenching experiments, electron paramagnetic resonance (EPR) and electrochemical characterization tests demonstrate that the degradation occurred via both radical and non-radical mechanisms. The differing types of reactive oxygen species (ROS) acting and the different electrostatic attraction between the materials and the two dyes lead to a significant difference in the removal effect of two dyes. The degradation mechanism is the redox reaction between Ni²⁺/Ni³⁺, Fe²⁺/Fe³⁺ and the synergistic effect of Ni³⁺/Fe²⁺. Finally, the biotoxicity assessment demonstrated that both the degradation intermediates of mixed dyes and the material itself exhibited low biotoxicity.