State-of-the-art synthesis strategy for nitrogen-doped carbon-based electromagnetic wave absorbers: from the perspective of nitrogen source

With the development of electronic science and information technology, electronic equipments relying on electromagnetic wave (EW) carriers have been widely used in various fields, while the consequent electromagnetic pollution has posed a great threat to human health and environment. The research and development of new types of electromagnetic wave absorption materials (EWAMs) are extraordinarily beneficial for addressing these issues and have attracted most of attentions. Nitrogen (N)-doped carbon materials possess many advantages including controllable dielectric loss, strong polarization effect, and abundant defect structures, which are helpful to enhance EW absorption performance. The electron offset caused by electronegativity of nitrogen and carbon atoms can enhance the EW absorption performances by means of dipole polarization. Then, molecular defects formed by N atom doping into the graphitization structure can also significantly attenuate the EW energy. Besides, dielectric loss, conductivity loss, and resonance effect can effectively improve the attenuation capacity. Therefore, design and synthesis of N-doped carbon-based EWAMs have been a research hotspot in recent years. Herein, the most widely used construction strategies of N-doped carbon involving N-incorporated small molecule doping and carbonization of N-containing precursors were discussed in detail. From the perspective of N source, urea, ethylenediamine, and hydrazine hydrate are the most commonly used small molecule nitrogen sources for high-performance EWAMs currently. And polypyrrole, melamine, 2-methylimidazole, polydopamine, polyacrylonitrile, and natural protein can serve as nitrogen sources of nitrogen-containing precursors. This review aims to help researchers deeply understand the synthesis strategies and reaction mechanisms in nitrogen source selection of N-doped carbon and develop efficient EWAMs.