Determination of surface free energy and acido-basicity of MXene materials measured by inverse gas chromatography at infinite dilution

Since the seminal report of Ti₃C₂T_x in 2011, MXene has emerged as a subject of considerable interest among researchers, finding diverse applications spanning energy storage, catalysis, and coatings. Despite extensive studies on the physicochemical properties of MXene, a comprehensive understanding of its surface energetics, free from environmental influences or external substitutes, remains lacking. This study aims to fill this gap by employing the inverse gas chromatography (IGC) technique at infinite dilution to delineate the London dispersive and specific components, alongside the Lewis acid-base characters, of surface free energy in MXene materials, including MAX phase and MXene. Our findings reveal that the London dispersive surface energy values of MAX phase and MXene range from 59.3 to 80.2 mJ m⁻² and 107.8–119.9 mJ m⁻², respectively, across temperature ranges of 303–333 K and 393–423 K. The observed augmentation in surface energy for MXene is attributed to a higher density of non-polar surface groups and an enlarged interlayer spacing. Additionally, our analysis indicates significantly higher acceptor (K_A) and donor (K_D) parameters for MXene (0.97 and 1.97, respectively) compared to MAX phase (0.41 and 0.63, respectively), suggesting a preference for the Lewis acid-base character in both materials, with MXene exhibiting a more pronounced tendency. These findings offer crucial insights into the fundamental surface energetic characteristics underlying multiple physicochemical properties of MXene. This understanding facilitates the informed design of interface engineering strategies, advancing the exploration and advancement of MXene-based technologies across a broad spectrum of applications.