MXenes: Fundamentals, properties, classification, and application

Discovered in 2011, MXenes are two-dimensional metal carbides or/and nitrides that are synthesized from precursors “MAX phases” (in which “M” depicts transition metal, “A” depicts elements from groups 13 to 16 of the periodic table, and “X” depicts carbon or/and nitrogen). Generally, selective etching is done to etch “A” layers from MAX phases to produce MXenes. Due to their unique properties like high electrical and thermal conductivity, high Young's modulus, magnetic ordering, negative-zeta potential, optical transparency, and photothermal conversion, MXenes are utilized in several applications like energy storage, sensors, biomedical, catalytic, photonic, and environmental applications. Moreover, surface terminations are also attached with MXenes as a result of etching which also influence their properties. Despite several useful applications, the synthesis of a few MXenes (out of hundreds of possible variations) has been practically achieved due to difficulty in the synthesis process. In such cases, density functional theory has aided the researchers to explore the possible characteristics of those MXenes that are not synthesized yet. This chapter presents a thorough history, fundamentals, properties, classification, and applications of MXenes covering the literature from the latest research works.