Fe3O4 core–shell catalysts supported by nickel foam for efficient heterogeneous electro-Fenton degradation of salicylic acid at neutral pH

A novel nickel foam (NF) supported core–shell catalytic material with excellent catalytic performance was successfully prepared for the degradation of salicylic acid (SA) by heterogeneous electro-Fenton (HEEF). Under the reaction conditions of SA initial concentration of 100 mg/L, catalyst dosage of 4 g/L, aeration rate of 0.1 L/min, current of 0.3 A and pH of 7, after 2 h, the removal efficiency of the progressively modified core–shell catalysts for SA and COD was as follows: NF@Fe 3 O 4 @SiO 2 @MgAl-LDH > NF@Fe 3 O 4 @MgAl-LDH > NF@Fe 3 O 4  > NF@Fe 3 O 4 @SiO 2 . The removal efficiency of NF@Fe 3 O 4 @SiO 2 @MgAl-LDH for SA and COD reached 72.8 % and 52.12 %, respectively. The morphology, composition and structural characteristics of the composite catalysts were analyzed and compared by a series of characterization methods. Among them, NF@Fe 3 O 4 @SiO 2 @MgAl-LDH showed the largest Fe:Ni atomic content ratio, specific surface area and pore volume, with values of 1: 2.62, 7.5405 m 2 ·g −1 and 0.010504 cm 3 ·g −1 , respectively. Radical quenching experiments, changes in H 2 O 2 and Fe 2+ ion concentrations, and X-ray photoelectron spectroscopy (XPS) analysis revealed the reaction mechanism of the HEEF process. That is, synergistic oxidation of active radicals and abundant adsorbed oxygen and lattice oxygen on the surface of the materials promoted the degradation and mineralization of SA. The excellent stability and reusability of NF@Fe 3 O 4 @SiO 2 @MgAl-LDH in the HEEF system were verified through five cyclic experiments with low material loss rate and sludge production.