Low temperature preparation of highly fluorinated multiwalled carbon nanotubes activated by Fe₃O₄ to enhance microwave absorbing property

Abstract

Conventional approaches to preparing highly fluorinated multiwalled carbon nanotubes (MWCNTs) always require a high temperature. This paper presents a catalytic approach to realizing the effective fluorination of MWNCTs at room temperature (RT). Fe₃O₄/MWCNTs composites with Fe₃O₄ loaded on MWCNTs were first prepared using the solvothermal method, followed by fluorination treatment at RT. The attachment of Fe₃O₄ changes the charge distribution and dramatically improves the fluorination activity of MWCNTs. Consequently, the fluorine content of fluorinated Fe₃O₄/MWCNTs (F-Fe₃O₄/MWCNTs) can reach up to 17.13 at% (almost six times that of the unloaded sample) only after fluorination at room temperature, which leads to an obvious decrease in permittivity. Besides, the partial fluorination of Fe₃O₄ brings about abnormally enhanced permeability due to strengthened exchange resonance. Benefiting from the lower permittivity and higher permeability, F-Fe₃O₄/CNTs composite exhibits increased impedance matching and thus an enhanced microwave absorption property with a minimal reflection loss of -45 dB at 2.61 mm when the filler content is 13 wt%. The efficient absorption bandwidth (<-10 dB) reaches 4.1 GHz when the thickness is 2.5 mm. This work illustrates a novel catalytic approach to preparing highly fluorinated MWCNTs as promising microwave absorbers, and the design concept can also be extended to the fluorination of other carbon materials.