Excellent Microwave Absorbing Property of Multiwalled Carbon Nanotubes with Skin-Core Heterostructure Formed by Outer Dominated Fluorination

It is attractive that excellent microwave absorbing materials with novel structure are prepared. In this work, we present a novel skin-core strctured fluorinated multiwalled carbon nanotubes (MWCNTs) microwave absorbing material through selective fluorination of the outer shell of MWCNTs. Fluorine gas (F-2) can attack defect sites to form CF2 at defect sites at low temperature. The preformed CF2 bond can prevent the permeation of F-2 into inner tubes, bringing about the mere fluorination of the outer skin with inner tubes intact at high temperature (the sample is denoted as F-h-MWCNTs). As a result, composed of an outer insulating skin and inner conductive tubes, F-h-MWCNTs behave as a skin-core heterostructure and show excellent microwave absorbing property with minimal reflection loss up to -69 dB at a thickness of 1.5 mm when the filler loading is only 9.1 wt %. Based on the investigation of electromagnetic behavior of a fluorinated single -walled carbon nanotube (SWCNT), the strong microwave absorption capacity of F-h-MWCNTs was attributed to the skin-core heterostructure. The outer skin is a fluorinated layer behaving with good impedance matching, which is conducive to the transmission of electromagnetic waves. The inner tubes maintain intact after direct heating fluorination and show a strong ability of attenuating electromagnetic waves. Meanwhile, F-h-MWCNTs possess better dispersibility in epoxy, making F-h-MWCNTs a proper candidate to prepare advanced an composite with strong absorption and good mechanical property.