  Nanolaminated materials are important because of their exceptional properties
and wide range of applications. Here, we demonstrate a general approach to
synthesize a series of Zn-based MAX phases and Cl-terminated MXenes originating
from the replacement reaction between the MAX phase and the late transition
metal halides. The approach is a top-down route that enables the late
transitional element atom (Zn in the present case) to occupy the A site in the
pre-existing MAX phase structure. Using this replacement reaction between Zn
element from molten ZnCl2 and Al element in MAX phase precursors (Ti3AlC2,
Ti2AlC, Ti2AlN, and V2AlC), novel MAX phases Ti3ZnC2, Ti2ZnC, Ti2ZnN, and V2ZnC
were synthesized. When employing excess ZnCl2, Cl terminated MXenes (such as
Ti3C2Cl2 and Ti2CCl2) were derived by a subsequent exfoliation of Ti3ZnC2 and
Ti2ZnC due to the strong Lewis acidity of molten ZnCl2. These results indicate
that A-site element replacement in traditional MAX phases by late transition
metal halides opens the door to explore MAX phases that are not
thermodynamically stable at high temperature and would be difficult to
synthesize through the commonly employed powder metallurgy approach. In
addition, this is the first time that exclusively Cl-terminated MXenes were
obtained, and the etching effect of Lewis acid in molten salts provides a green
and viable route to prepare MXenes through an HF-free chemical approach.
