Order effect of nitrogen and phosphorus co-doping carbon nanofibers for enhancing electromagnetic wave absorption

In this work, N, P co-doped carbon nanofibers (CNF-NP and CNF-PN) were successfully synthesized by a two-step pyrolysis, and the effect of doping orders on microwave absorption (MA) was investigated for the first time. It was found that graphitic-N produced from the first N-doping suppressed the formation of C3PO due to the competition of doping sites for CNF-NP. Therefore, extra P atoms combined with oxygen-containing groups formed lots of C-OPO3 during the subsequent P-doping. However, for CNF-PN large amounts of C3PO were easily formed when P atoms were first doped, which limited the production of graphitic-N and resulted in the ratio improvement of pyrrolic-N and pyridinic-N. It was found that the ratios of different doping sites obviously influenced the MA performance. CNF-PN exhibited the minimum reflection loss (RLmin) value of -55.0 dB at 2.3 mm and effective bandwidth (EAB) of 6.6 GHz, attributing to the dielectric loss increased by an appropriate ratio of C-OPO3 and a high ratio of pyrrolic-N and pyridinic-N. In contrast, RLmin of CNF-NP was only -30.8 dB at 1.7 mm with the EAB of 3.3 GHz, due to the impedance mismatching from too much C-OPO3. This work sheds new light on adjusting MA properties by doping orders, which is of great significance for the development of novel absorbers based on carbon nanofibers.

Automated summary

In this work, N, P co-doped carbon nanofibers (CNF-NP and CNF-PN) were synthesized and the effect of doping orders on microwave absorption (MA) was investigated. It was found that graphitic-N produced from the first N-doping suppressed the formation of C3PO, while for CNF-PN large amounts of C3PO were easily formed when P atoms were first doped. The ratios of different doping sites obviously influenced the MA performance, with CNF-PN exhibiting better MA properties due to appropriate ratios of C-OPO3 and pyrrolic-N/pyridinic-N.