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Nitrogen Doped Carbon Nanosheets Homogeneously Imbedded With Co Nanoparticles via Biostructure Confinement as Highly Efficient Microwave Absorbers

2D/quasi-2D nanomaterial (e.g., graphene, MXene, carbon nanosheet) based composites are efficient absorbers of the ever-growing pollution of electromagnetic wave (EMW) due to their large aspect ratios, ample functional groups and tunable electric and magnetic properties. However, a simple and cost-effective synthesis process of the nanocomposites is still elusive. Thus, we demonstrated a simple swelling and carbonization process of exfoliated cellulose fibril to synthesize nitrogen-doped carbon nanosheets with homogeneously imbedded Co nanoparticles (Co/NCN). Co/NCN with carbonization temperature of 800 °C exhibited a minimum reflection loss (RLmin) of -65.7 dB at 13.9 GHz and an effective absorption bandwidth of 5.8 GHz with RL <-10 dB at a thickness of 1.7 mm. In addition, the microwave absorption characteristics of the composite can be further adjusted by the carbonization temperature. Those value are superior to many nanocomposites based on graphene and MXene. The doped nitrogen heteroatoms were found to be important for maintaining the morphology of carbon nanosheet, increasing the interfacial polarization loss and improving the impedance matching. The environment-friendly and low-cost process proposed here can be extended to synthesis many other metal/NCN nanocomposites as the high-performance EMW absorbers.