Compositions comprising free-standing two-dimensional nanocrystals

A method of transferring urea from an aqueous solution to a MXene composition, the method comprising contacting an aqueous solution comprising urea with the MXene composition for a time sufficient to form an intercalated MXene composition comprising urea;

• wherein
• the MXene composition comprises a stacked assembly of at least two layers, each layer having first and second surfaces, each layer comprising:
• a substantially two-dimensional array of crystal cells,
• each crystal cell having the empirical formula of Mn+1Xn, such that each X is positioned within an octahedral array of M;
• wherein M is at least one Group IIIB, IVB, VB, or VIB metal;
• each X is C, N, or a combination thereof;
• and
• n=1, 2, or 3;
• and wherein
• the layers are characterized as having an average surface area;
• and
• at least one of said surfaces of each layer has bound thereto surface terminations comprising alkoxide, carboxylate, halide, hydroxide, hydride, oxide, sub-oxide, nitride, sub-nitride, sulfide, thiol, or a combination thereof.