Controllable synthesis of N-doped carbon nanoparticles with proper electrical conductivity for excellent microwave absorption performance

•N-doped carbon nanoparticles are synthesized by heat treatment on phenolic resin.•The σ of carbon were tuned by morphology, diameter and graphitization degree.•Microwave absorption (MA) properties of carbon were intensively affected by the σ.•The total σ of composites with order of magnitude of 10-1 S/m is proper for MA.•Carbon nanoparticles with σ of 0.61 S/m show effective bandwidth of 6.7 GHz.