Rational design of MXenes as multifunctional quantum materials: structure tuning of electronic, optical, and magnetic properties

MXenes, a rapidly expanding family of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides, exhibit metallic conductivity, a large specific surface area, and highly tailorable surface chemistry. These distinctive physical and chemical attributes have stimulated intense interest in MXenes as emerging multifunctional quantum materials with promising applications in energy storage, sensing, catalysis, and electronic/optoelectronic devices. In this review, we focus on the rational design strategies that can enable us to control and optimize the electronic, optical, and magnetic properties of MXene structures. We systematically discuss how tuning the M- and X-site elements, surface functional groups, guest intercalants, structural defects, and layer number, as well as applying strain, enables precise modulation of MXenes' layered architectures and associated properties. Particular emphasis is placed on the structure–property relationships that govern charge transport, optical response, spin behavior, and quantum phenomena in MXenes. We further highlight the design principles for tailoring MXenes’ layered structures and surface chemistry to meet specific requirements in electronic, optical, and magnetic applications. Finally, we outline key challenges and future research directions, including scalable fluoride-free synthesis, deterministic termination control, stability and device-level reliability, and experimental validation of the predicted magnetism in guiding material design. This review aims to provide a comprehensive and timely overview of MXenes as multifunctional quantum materials, offering a framework that can accelerate the discovery and deployment of next-generation MXene-based technologies.