Fe-Ti oxides/carbon composites derived from temperature-dependent solid-state reaction between MOFs core and TiO2 shell for broadband microwave absorption

Abstract

Regulating phase composition and dispersion state of oxide particles inside metal-organic frameworks-derived carbon composite holds enormous potential in enhancing dielectric property and microwave absorption performance. Herein, solid state reaction between Fe-bdc nanorod and TiO2 shell has been used to synthesize a series of Fe-Ti oxides/carbon (FTO/C) composites at different annealing temperatures. The results show that with the increase of temperature, the grain size of oxide particles, which tend to distribute in the center of carbon rod, has increased, resulting in the formation of continuous conductive surface caron layer. Meanwhile, the aspect ratio of carbon rod would decrease, which would hinder the construction of conductive path in paraffin matrix. At lower temperature, internal oxide particles are less crystallized (Fe2.5Ti0.5)1.04O4, which may induce obvious dipole polarization. While at higher temperature, phase conversion from (Fe2.5Ti0.5)1.04O4 to Fe2TiO4 and FeTiO3 would bring about more interfaces, which generate strong interfacial polarization. Therefore, dielectric loss of as-prepared FTO/C composites would be enhanced with rising temperature until 700 oC, and impedance matching condition would always be improved with increasing temperature, in terms of lowest matching thickness in whole Ku or X bands. Consequently, S-700 owns a broad effective absorption bandwidth (EAB) of 6.84 GHz at 2.2 mm, covering whole Ku band and S-800 owns a large EAB of 4.16 GHz at 2.8 mm, covering whole X band. This work may provide novel insights into the design of metal-organic frameworks-derived carbon composite with desired dielectric properties through controlling the composition and dispersion of inner oxide particles.