Controllable Synthesis of γ-Fe2O3 Nanotube/Porous rGO Composites and Their Enhanced Microwave Absorption Properties

γ-Fe2O3 nanotube/porous reduced graphene oxide (rGO) composites were prepared using a controllable method. Uniform γ-Fe2O3 nanotubes with a diameter of about 85 nm and a length of about 230 nm are well distributed between porous rGO sheets. Compared with the γ-Fe2O3 nanorod/porous rGO and γ-Fe2O3 nanotube/nonporous rGO, the γ-Fe2O3 nanotube/porous rGO composites with both unique hollow and porous structure show an advantage for the attenuation of microwaves. The appropriate dielectric loss and magnetic loss result in a good impedance matching. The minimum reflection loss of γ-Fe2O3 nanotube/porous rGO composite reaches −34.20 dB with a thickness of 2.0 mm, and the absorption bandwidth is 4.59 GHz. These results reveal that the synthesis of hollow and porous composites is a promising way for getting lightweight microwave materials with high performance.