Surface-terminated MXenes to act as dynamic solid-liquid interfaces: Enhancing colloidal stability and interfacial...

MXenes are a rapidly expanding family of two-dimensional transition-metal carbides, nitrides, and carbonitrides whose physicochemical behavior in aqueous and biological environments is dominated by their surface terminations (e.g., -O, -OH, and -F), rendering them intrinsically active solid-liquid interfaces. These terminations regulate interfacial charge distribution, hydration structure, adsorption equilibria, and colloidal stability, positioning MXenes as dynamic interfacial systems rather than passive nanomaterials. Rational control of surface termination chemistry therefore represents a central strategy for governing MXene interactions with electrolytes, proteins, and biological media. This review provides a comprehensive and critical analysis of recent advances in MXene surface-termination engineering from the perspective of interfacial and colloidal science, with emphasis on etching routes, post-synthetic modification, dimensional tailoring (2D, 3D, and emerging 4D architectures), and characterization approaches relevant to interfacial behavior. We examine how termination chemistry controls key interfacial properties, including zeta potential, dispersion stability in physiological electrolytes, hydration-mediated wetting, and protein corona formation, and how these interfacial factors collectively shape biological responses such as cytotoxicity, inflammatory signaling, antibacterial activity, and reactive oxygen species generation. Particular attention is devoted to termination-driven charge regulation and coordination chemistry at solid-liquid interfaces, which govern adsorption-desorption dynamics, molecular loading, and stimulus-responsive release, as well as the modulation of optical and magnetic responses. By critically comparing reported systems and explicitly addressing unresolved challenges related to termination heterogeneity, interfacial aging, and scalability, this review clarifies structure-interface-function relationships that underpin MXene performance in complex environments. Finally, we identify emerging strategies and open questions for designing surface-terminated MXenes with predictable and controllable interfacial behavior, highlighting their broader relevance as model systems for dynamic solid-liquid interfaces with bio-functional implications.