Regulating surfactant strategy to synthesize Co@NCNT nanocomposites with conductive networks towards excellent electromagnetic wave absorption

•The effect of surfactants on the morphology of Co-PBA was investigated.•Co@NCNT composites derived from PBAs with porous cubic structure were prepared.•The minimum reflection loss reached - 43.95 dB at a thickness of 2.05 mm.•The effective absorption bandwidth was 5.695 GHz at a thickness of 2.05 mm.•The excellent properties are attributed to the dielectric and magnetic synergy.