Foldable polyimide composite films assembled with highly transparent 2D3D heterogeneous MXene/Ln3+@UiO-66: Exceptional ultraviolet resistance

Both the 2D titanium carbide (Ti 3 C 2 T x ) MXene and the 3D rare earth doped zirconium-based metal organic framework (Ln 3+ @UiO-66, MOF) were constructed on the colorless transparent polyimide (CPI) film to form the heterojunction multifunctional nano-coating via a one-pot immersion method in order to improve the UV resistance of CPI. Firstly, the S/CPI film was obtained via the CPI being modified with silica (SiO 2 ) sol, and then the Ti 3 C 2 T x MXene was loaded onto the surface of the S/CPI film via the hydrogen bond, finally the Ln 3+ @UiO-66 was loaded onto the ultra-thin Ti 3 C 2 T x MXene nanosheets to obtain optimal sample (MXene/Ln 3+ @UiO-66-S/CPI). The transmittance of MXene/Ln 3+ @UiO-66-S/CPI is 93.33%, which is only 0.94% lower than that of S/CPI. The tensile strength and elongation of MXene/Ln 3+ @UiO-66-S/CPI are basically the same as those of S/CPI. The attenuation values of transmittance, tensile strength, and elongation for MXene/Ln 3+ @UiO-66-S/CPI film after 5000 equivalent sun hours (ESHs) UV irradiation are 2.44%, 10%, and 18%, respectively, i.e., this film gets both a high transparency and a super ultraviolet resistance. This may be attributed to the fact that the MXene/Ln 3+ @UiO-66 multifunctional nano-coating can absorb the UV light and undergo the down-conversion, weakening the UV irradiation intensity.