Large-Scale Nanofiber Manufacturing| Controlled preparation of lightweight, resilient helical carbon fibers forhigh-performance microwave absorption and oil-water separation

The rapid development of next-generation communication devices has intensified electromagnetic radiation pollution, creating demand for effective microwave absorption (MA) materials. Helical materials, with their unique structural and optical properties, have emerged as promising candidates due to their additional chiral parameters and ability to generate cross-polarization through structural chirality. Among these, helical carbon nanotubes (HCNTs) and helical carbon nanofibers (HCNFs) stand out for their lightweight nature, suitable conductivity, and cross-polarization induction capability, making them highly attractive for MA applications.

Recently, the research team led by Dr. Ying Li from Chengdu University published their latest findings titled "Controlled preparation of lightweight, resilient helical carbon fibers for high-performance microwave absorption and oil-water separation" in the journal Carbon. The researchers achieved large-scale production of straight (CNFs), twisted (TCNFs), and spring-like (SCNFs) carbon fibers through improved precipitation/sol-gel/reduction technology combined with chemical vapor deposition. Compared to CNFs, the two types of helical carbon nanofibers exhibited superior hydrophobic properties and MA performance. The excellent electromagnetic wave absorption capability is attributed to the synergistic effect of dielectric and magnetic losses, while the helical structure induces cross-polarization, further enhancing MA performance. Additionally, both TCNFs and SCNFs demonstrated good elasticity and hydrophobic-oleophilic characteristics. Overall, these findings provide valuable insights for developing lightweight, high-performance materials and open new possibilities for designing multifunctional devices.

Figure 1b shows the morphology of CNFs, with diameters ranging from 100 to 260 nm. TCNFs have shorter diameters than CNFs, measuring between 50 and 110 nm (Figure 1c). SCNFs exhibit more coiled structures with smooth surfaces, having pitch diameters of 1.75-2.9 μm, pitch distances of 40-380 nm, and tube diameters of 210-450 nm (Figure 1d).

Figures 2a-c present the RL characteristics of CNFs, showing an RLmin value of -16.4 dB at 17.8 GHz, barely meeting the practical requirement of -10.0 dB. For TCNFs (Figures 2d-f), the RLmin reaches -41.2 dB at 7.8 GHz with a thickness of 3.9 mm. At 1.78 mm thickness, the EAB is 4.8 GHz (13.2-18.0 GHz). In Figures 2g-f, SCNFs achieve an RLmin of -50.4 dB at 10.3 GHz with 2.5 mm thickness. At 1.74 mm thickness, the EAB extends to 4.1 GHz (13.9-18.0 GHz). The excellent electromagnetic wave absorption performance of TCNFs and SCNFs can be attributed to the synergistic effect of dielectric and magnetic losses, with the helical structure inducing cross-polarization.

Both TCNFs and SCNFs exhibit not only excellent electromagnetic wave absorption performance but also hydrophobic properties. Figures 3a-c illustrate the hydrophobic characteristics of the three different carbon nanofiber morphologies. CNFs and TCNFs demonstrate contact angles of 110.5° and 124.0° respectively, indicating good hydrophobicity and qualifying as hydrophobic materials with MA capability. Due to their internal coiled spring-like structure, SCNFs display superior hydrophobicity with a contact angle reaching 151.3°, classifying them as superhydrophobic materials. Figures 3d-f show SCNFs' adsorption behavior towards water and oil. The material exhibits hydrophobicity while demonstrating strong oil absorption capacity within short periods, with an oil contact angle of 0°, confirming SCNFs' superhydrophobic and oleophilic nature that enables selective adsorption of oil contaminants. These findings provide valuable insights for multifunctional applications of carbon materials.