A novel Co/TiO2 nanocomposite derived from a metal-organic framework: synthesis and efficient microwave absorption

To overcome the shortcomings (poor impedance mismatching and weak electromagnetic wave attenuation) of the Co nanoparticles embedded into nanoporous carbon (Co@NPC) derived from the thermal decomposition of zeolitic imidazolate framework-67 (ZIF-67), two coated titanium oxide (TiO2) routes are designed to prepare core-shell Co@NPC@TiO2 and multi-interfaced yolk-shell C-ZIF-67@TiO2 (obtained from the thermal decomposition of ZIF-67@TiO2) structures. The permittivity and permeability of C-ZIF-67@TiO2 significantly depend on the thickness of the TiO2 shell in ZIF-67@TiO2, and the thickness of the TiO2 shell in the as-obtained samples can be easily controlled via changing the addition content of tetrabutyl titanate in the hydrolyzation process. The as-prepared samples have remarkable absorbing characteristics in wide frequency bands from 2-18 GHz with thicknesses of 1.0-5.0 mm. 50 wt% of the C-ZIF-67@TiO2-2 (the addition amount of tetrabutyl titanate is 2 mL) nanocomposite filled within paraffin shows a maximum reflection loss (RL) of -51.7 dB at an absorbing thickness of 1.65 mm, meanwhile, for the Co@NPC@TiO2-1.2 (the addition amount of tetrabutyl titanate is 1.2 mL) nanocomposite, a maximum RL can be achieved of -31.7 dB at 1.5 mm. This study provides a good reference for the future preparation of other carbon-based lightweight microwave absorbing materials derived from metal organic frameworks.