Preparation and tailoring electromagnetic shielding and microwave absorbing performance of Fe₃O₄ modified activated carbon foam based on mesophase coal pitch pyrolysis foaming

The development of materials with excellent microwave absorption (MWA) and electromagnetic interference (EMI) shielding performances has currently received attention. Herein, mesophase pitch-based carbon foam (MPCF) with 3D interconnected pore structure was prepared through the high pressure pyrolysis of mesophase coal tar pitch. It is found that the 3D interconnected cellular pores of MPCF facilitate multiple reflections of electromagnetic waves, which results in the minimum reflection loss (RLmin) value of MPCF reaches −37.84 dB with the effective absorption bandwidth (EAB) of 5.44 GHz at a thickness of 2.70 mm, and the total average electromagnetic shielding effectiveness (SET) under 3.00 mm thickness achieves 26.52 dB in X-band. Subsequently, MPCF is activated by KOH to obtain activated carbon foam (A-MPCF). The average SET of A-MPCF achieves 103.00 dB for abundant nanopores on the pore cell walls, which leads to a transition from the multiple reflections of electromagnetic waves on the walls to diffuse reflection. Unfortunately, the reflection coefficient (R) of A-MPCF increases from 0.78 to 0.90. To reduce the R value, Fe3O4/A-MPCF was fabricated via the in situ growth of nano Fe3O4 on A-MPCF. Consequently, the R value of Fe3O4/A-MPCF was reduced from 0.90 to 0.74, whereas the MWA performance was only slightly decreased. This work proposes a simple strategy for simultaneously adjusting MWA and EMI shielding performances of materials.