Flexible Ti₃C₂T_x MXene-Cellulose Nanofiber Membranes—Structural and Optical Functioning

Controlled organization of Ti₃C₂T<i>_x</i> MXene within polymer networks is crucial for harnessing its full potential as a versatile 2D material across a broad spectrum of applications. Cellulose nanofibers (CNFs), extracted from natural plant sources, are biodegradable and characterized by a high aspect ratio, providing a large interface area for interaction with MXene flakes. In this study we investigate the fundamental properties and interactions between cellulose nanofibers (CNFs) and Ti₃C₂T<i>_x</i> MXene flakes, focusing on a unique CNF-dominant mixture with distribution of MXene flakes in flexible free-standing membranes obtained via vacuum assisted filtration. Unlike conventional MXene-CNF composites, which emphasize MXene's predominance for enhanced conductivity and mechanical strength, this research reverses the typical ratio, exploring the impact of MXene flake organization within a nanofiber matrix allowing to observe unique optical properties and photonic behavior of the membranes. These flexible and strong membranes demonstrate layered structure, high optical transparency up to 85% with a volume fraction of MXene flakes &lt; 1%. Our study reveals that the Ti₃C₂T<i>_x</i>/CNFs composite membranes, with a thickness of 3-4 microns exhibit unique color variations for flakes under bright field reflection mode from the multiple scattering events within the disordered structure of the Ti₃C₂T<i>_x</i> flakes in the cellulose matrix. This work’s discovery expands our understanding of Ti₃C₂T<i>_x</i>/CNFs composites, illustrating their potential for advanced photonic applications.