Abstract:

Objective The widespread applications of electronic devices result in serious electromagnetic radiation pollution problems, and the development of efficient electromagnetic shielding materials is imminent. Carbon nanofiber (CNF) membranes prepared by electrospinning, as a type of carbon-based materials with light weight, large aspect ratio and corrosion resistance, have attracted extensive research attention. The MXene modified CNF membrane can improve the conductivity of the membrane material and enhance the electromagnetic shielding efficiency. However, the conventional in-situ spinning, and dipping methods exhibited low efficiency and uneven effect. Therefore, achieving efficient uniform modification remains a challenge for CNF-based electromagnetic shielding materials. This research proposes an electrophoretic deposition (EPD) method using CNF membrane as anode to complete MXene uniform load within a very short time.

Method A thin layer negatively charged MXene was obtained by etching MAX with in-situ synthesis of hydrofluoric acid. A highly oriented polyacrylonitrile (PAN)-based nanofiber membrane was prepared by electrospinning technology. The cyclic dehydrogenation reaction of the polymer was completed by peroxidation treatment at 250 ℃, and the cross-linking and densification reactions were carried at 900 ℃ and 1 400 ℃. CNF with certain conductivity was obtained.

Results In-situ synthesized hydrofluoric acid etching and stripping were employed to obtain layers of MXene with a clean and smooth surface. Zeta potential characterization demonstrated the negative charge on the lamella surface, providing a theoretical basis for the anodic electrodeposition method. The PAN-based nanofiber membrane was spun by electrospinning technology. After pre-oxidation and carbonization treatment, CNF membrane with high orientation was obtained. The CNF had amorphous graphite structure, which was the source of the conductivity of the membrane. The efficient combination of MXene and CNF was achieved by the EPD method. The CNF was fixed to the anode, and the negatively charged MXene was drawn to the surface of the CNF under the action of an electric current. With the increase of deposition voltage and time, the uniformity of lamellar coverage was improved. When the deposition voltage was 5 V and the deposition time was 10 min, the composite membrane showed the best morphology. The surface of the fiber was covered with a continuous layer of MXene, with the adjacent layers touching each other. The pores between the nanofibers in the membrane were filled with MXene, and the independent fiber membranes were connected through the MXene layer. With the increase of deposition voltage and time, the amount of MXene deposition was increased. However, high voltage (10 V) led to TiO₂ on the surface of the composite membrane, and MXene oxidation degradation occurred. The surface deposition of MXene significantly improved the conductivity of the membrane material. Compared with the conductivity of the original PAN-CNF membrane that is 2 406 S/m, when the treatment conditions were 5 V and 10 min, the conductivity of the Mxene/CNF composite membrane reached 4 424 S/m, representing an increase by 83%. In terms of the electromagnetic shielding performance, the electromagnetic shielding performance of nanofiber membrane treated by electrodeposition MXene was improved compared with PAN-CNF membrane. It was found that electromagnetic shielding performance was positively correlated with the electrical conductivity, up to 25.96 dB and representing an increase by 112%. The shielding efficiency of the composite membrane in electromagnetic wave band of 8-12 GHz was 99.75%, indicating that only 0.25% electromagnetic wave could pass through the composite membrane, achieving a good shielding effect.

Conclusion MXene and CNF were uniformly recombined efficiently by electrodeposition. The introduction of conductive MXene significantly improved the electromagnetic shielding performance of carbon-based nanofiber membranes. The excellent electromagnetic shielding performance of MXene/CNF composite membranes could be attributed to its abundant internal conductive paths, which led to polarization relaxation and numerous heterogeneous interfaces, which prolonged electromagnetic wave attenuation paths and enhanced multiple reflection and scattering. The high-efficiency electromagnetic shielding composite membrane is expected to be applied in the field of electromagnetic protection of wearable devices.

Key words: MXene, carbon nanofiber membrane, electrospinning, electrophoretic deposition, electromagnetic shielding