Unraveling the carbon dot bridges in oxidized carbon nanotubes for efficient microwave absorption

Carbon nanotube (CNT)-based composites hold immense promise in the realm of electromagnetic (EM) wave absorption. Surface functionalization of CNTs plays a pivotal role in augmenting their surface binding energy, thereby bolstering their affinity for composites. However, the incorporation of functional groups may disrupt the electronic configuration of sp2 plus delocalized π-bonds and impede electronic transport within the CNT framework. Herein, carbon dots (CDs) were introduced onto the surface of oxidized CNTs (O-CNTs) using a one-step hydrothermal method to enhance their bonding capability and microwave absorption performance. Analysis showed that the characteristic functional groups on the surfaces of the CDs formed amide bonds between the CNTs, bridging them with π-conjugated structures and repairing the blocked electron transport pathway triggered by carboxyl groups. The bridging accelerated the electron flow between adjacent CNTs and enhanced the electron jumping and migration in the CDs-CNTs system. Additionally, a comprehensive investigation of the heterogeneous charge distribution within the CDs bridges and their tunable band gap demonstrated their significant influence on polarization relaxation and conduction loss. In short, the study presents a novel functionalization theory for CNTs that exhibit remarkable microwave-absorption performance in X-band.