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 CF 2 at defect sites at low temperature. The preformed CF 2 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.