Effect of structural optimization of magnetic MnFe2O4@Bi24O31Br10/Bi5O7I with core-shell structure on its enhanced photocatalytic activity to remove pharmaceuticals

Abstract

Pharmaceutical contamination spreading across the aquatic environment has resulted in great disturbance to ecosystem and severe menace to human health. Magnetic photocatalysts have achieved great attention due to their magnetic separation capacity, recycling usage and low risk for secondary pollution. However, their practical applications to solve pollution problem are limited due to the insufficient photocatalytic activity, which is caused by their low valence band potentials and fast recombination of photo-generated carriers. In our research, by involvements of layer-structured bismuth-rich oxyhalides (BixOyXz, X = Cl, Br, I), optimizations for the microstructure and band structure of magnetic MnFe2O4 were applied to improve its photocatalytic activity for effectively removing pharmaceuticals residues. With the assistance of Bi24O31Br10 and Bi5O7I, MnFe2O4 nanoparticles (NPs) was gradually optimized to core-discontinuous shell structure of MnFe2O4@Bi24O31Br10 (M@B) and multi-layer entire core-shell structure of MnFe2O4@Bi24O31Br10/Bi5O7I (M@B/B). The optimized microstructures of M@B and M@B/B provide tight contact between components and promote the separation and utilization rates of carriers in photocatalytic process. For ternary M@B/B, tight contact between the components permits the working of optimized band structure, where double-Z scheme is formed and a favorable electron transfer mode is allowed. The production rates of active radicals from CB of Bi5O7I and VB of MnFe2O4 and Bi24O31Br10 are promoted and their redox abilities are strengthened. The synergy of improved utilization rate of carriers and their strengthened redox ability endows M@B/B with superior photocatalytic performance for removing pharmaceuticals with high concentrations. The removal efficiencies of M@B/B are determined to be 93.2%, 95.0% and 87.8% in 100 min for levofloxacin (LVFX, 20 mg L−1), tetracycline (TC, 50 mg L−1) and triclosan (TCS, 100 mg L−1), respectively. Our research provides a novel and effective channel to improve the photocatalytic activity of magnetic materials by involvements of BixOyXz compounds. According to its enhanced photocatalytic performance, suitable magnetic separation capacity and recycling usage, the practical applications of MnFe2O4 magnetic composites to treat real pharmaceuticals wastewater are reasonable and realistic.