Rational Design of Superior Microwave Shielding Composites Employing Synergy of Encapsulating Character of Alginate Hydrogels and Task-Specific Components (Ni NPs, Fe₃O₄/CNTs)

Three-dimensional (3D) porous magnetic carbonaceous bead-like (MCB) composites (SA-Ni-(Fe 3 O 4 /CNTs)- X; SA stands for sodium alginate, CNTs means carbon nanotubes and X means Fe 3 O 4 /CNTs percentage) have been successfully fabricated through a facile one-step encapsulation process, followed by carbonization at 600 °C in nitrogen atmosphere. These magnetic nickel nanocrystals and Fe 3 O 4 /CNTs were uniformly dispersed into the entire porous carbon matrix without aggregation; and various techniques like scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and vector network analyzer (VNA) were conducted to demonstrate the morphology, structure, chemical content and electromagnetic parameters of the SA-Ni-(Fe 3 O 4 /CNTs)- X composites. The effect of the Fe 3 O 4 /CNTs molar percentage on the electromagnetic parameters and electromagnetic wave absorbing properties of the SA-Ni-(Fe 3 O 4 /CNTs)- X composites were investigated in the frequency range of 2–18 GHz. It was proven that the composites would be superior lightweight microwave absorbers when the Fe 3 O 4 /CNTs molar percentages were relatively high. When a 25% Fe 3 O 4 /CNTs molar percentage was used, it could lead to a maximum reflection loss (RL) of −32 dB at 10.8 GHz even with a thickness of 2 mm; the effective microwave absorption bandwidth (RL < −10) reached 3.2 GHz (from 9.3 to 12.5 GHz). The superior electromagnetic wave absorbing properties could be assigned to the high attenuation, Debye relaxation, electric polarization, interfacial polarization and high conductivity of the task-specific components. It is thus considered that the newly synthesized SA-Ni-(Fe 3 O 4 /CNTs)- X composite could be a promising candidate for novel types of lightweight and high-performance electromagnetic wave absorbing materials with great potentiality in practice.