Construction of gradient conductivity cellulose nanofiber/MXene composites with efficient electromagnetic interference shielding and excellent mechanical properties

The development of electronic communication technology leads to a complex electromagnetic (EM) environment, which is urgent for the design of high-performance EM interference (EMI) shielding materials. In this work, cellulose nanofiber (CNF) and MXene were used to construct ordered multi-layer composite films with a controllable conductive gradient by layer-by-layer vacuum filtration method. Especially, the films were composed of four transition layers (with low MXene content) and one reflection layer (with high MXene content), which not only effectively reduced the reflection of EM waves on the surface of materials but also greatly increased the multiple internal reflections of reflected EM waves. Besides, the dielectric loss provided by MXene, and the coordination of polarization with loss at the interfaces contribute to the outstanding EMI shielding effectiveness (EMI SE) (39 dB) and absorption effectiveness (28 dB) of the films. And practical application simulation proves that the composite membrane can limit the mobile phone communication signal. Moreover, the nacre-like structure was constructed by 1D CNF and 2D MXene, resulting in high tensile strength of 90.5 +/- 6.7 MPa and elongation at a break of 8.0 +/- 1.0%. Therefore, this work provided a feasible approach for preparing gradient composite films with high EMI shielding and mechanical properties, which is highly promising to be a competitive candidate for the application in the new-generation of intelligent electronic devices.