Influence of Chitosan Molecular Weight on the Functionalization and Interfacial Architecture of Ti3C2Tx MXene Composites

Abstract

The influence of chitosan (CS) molecular weight on the interfacial architecture of Ti3C2Tx MXene (MX)/chitosan composites (CS/MX) was investigated using complementary spectroscopic and microscopic techniques. Two commercial chitosans with distinct molecular weights and degrees of deacetylation (DD) were evaluated, CS-1 (91 kDa, 73.05% DD) and CS-2 (153 kDa, 69.52% DD). Ti3C2Tx MXene was synthesized by selective etching of Ti3AlC2 and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), and Raman spectroscopy. XPS and Raman analyses provided evidence for successful MXene formation through a 45.4% reduction in surface aluminum content, a substantial increase in fluorine-containing surface terminations, and the emergence of the characteristic A1g(Ti,C) Raman mode at ~200 cm−1. Composite membranes containing different MXene loadings (MX-25, MX-50, and MX-75) were prepared by vacuum-assisted filtration and characterized. Morphological and spectroscopic analyses revealed that the lower-molecular-weight chitosan promoted more effective intercalation between MXene layers, resulting in expanded accordion-like structures and greater surface accessibility. In contrast, the higher-molecular-weight chitosan formed a thicker polymer coating that partially encapsulated the MXene sheets. ATR-FTIR, Raman, and XPS results demonstrated that CS-MX composite formation was governed by non-covalent interactions, primarily electrostatic attraction between protonated chitosan –NH3+ groups and negatively charged MXene surface terminations, reinforced by hydrogen bonding. These findings demonstrate that chitosan molecular weight is a key design parameter governing the interfacial architecture and surface accessibility of Ti3C2Tx-based composites.