Two-dimensional (2D) materials often possess high specific areas and electronic properties distinct from their bulk counterparts. Recently, we discovered a family of 2D transition metal carbides and carbonitrides, which were called MXenes. They have a general formula of M_(n+1)X_nT_x, where M is an early transition metal, X is carbon or nitrogen, and T are surface functional group (e.g. -O, -OH, -F), due to being synthesized by selective etching of the "A" layers (Group 13,14 elements) from the M_(n+1)AX_n phases, a large family of ternary nanolaminated carbides and nitrides. MXenes have been found to be good electronic conductors and hydrophilic, in addition to having the ability to intercalate various Group I and II cations and swell in water like clays. As a result, they have been investigated for applications such as secondary metal-ion batteries, supercapacitors, water purification, photocatalysis, and transparent conductive electrodes.
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