Yolk-shell Co3O4@Fe3O4/C Nanocomposites as a Heterogeneous Fenton-like Catalyst for Organic Dye Removal

Graphical MB and PMS are absorbed by the Fe 3 O 4 /C shell and subsequently diffuse into the interior cavity of the yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites. PMS enter the catalyst and interact with active sites on the shell and in the core. Co 2+ and Fe 2+ in the catalyst can activate PMS to generate SO 4 ⋅ − . Meanwhile, OH − /H 2 O will be oxidized by SO 4 ⋅ − to ⋅OH, generating H + while consuming OH − . SO 4 ⋅ − , ⋅OH and , resulting from a typical chain reaction, will interact with MB and breakdown it to intermediates CO 2 and H 2 O. The yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites with Co 3 O 4 as the core, Fe 3 O 4 /C as the shell, and a cavity structure were synthesized by the hard template method. The physical and chemical properties of the composites were characterized by SEM, TEM, XRD, TGA, XPS, BET, and VSM. The specific surface area of yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites is 175.9 m 2 g −1 , showing superparamagnetic properties. The yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites were used as heterogeneous Fenton catalysts to activate peroxymonosulfate (PMS) to degrade MB, which showed high catalytic degradation performance. The degradation rate of MB reached 100 % within 30 min under the circumstances of the yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites dosage of 0.1 g L −1 , the PMS dosage of 1.0 g L −1 , the initial MB concentration of 100 mg L −1 , an initial pH of 5.5, and a temperature of 30±2 °C. The enhanced catalytic performance of the yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites can be attributed to the synergistic effect of the two catalytically active materials and the middle cavity. The effects of different operating parameters and co-existing anion species on MB degradation were also investigated. Electron paramagnetic resonance (EPR) analysis and quenching experiments confirmed that the formation of SO 4 ⋅ − in the yolk-shell Co 3 O 4 @Fe 3 O 4 /C/PMS system contributes to MB degradation. In addition, yolk-shell Co 3 O 4 @Fe 3 O 4 /C nanocomposites can be easily separated from the pollutant solution under the action of an external magnetic field, and the degradation rate of MB can still reach 98 % after five cycles, indicating that it has good stability and reusability and has broad application prospects in the field of water purification.