posted on 2021-09-15, 14:39authored byIan J. Echols, Hyosung An, Junyeong Yun, Kasturi T. Sarang, Ju-Hyun Oh, Touseef Habib, Xiaofei Zhao, Huaixuan Cao, Dustin E. Holta, Miladin Radovic, Micah J. Green, Jodie L. Lutkenhaus
MXenes,
2D nanomaterials derived from ceramic MAX phases, have
drawn considerable interest in a wide variety of fields including
energy storage, catalysis, and sensing. There are many possible MXene
compositions due to the chemical and structural diversity of parent
MAX phases, which can bear different possible metal atoms “M”,
number of layers, and carbon or nitrogen “X” constituents.
Despite the potential variety in MXene types, the bulk of MXene research
focuses upon the first MXene discovered, Ti3C2T. With the recent discovery of polymer/MXene multilayer assemblies
as thin films and coatings, there is a need to broaden the accessible
types of multilayers by including MXenes other than Ti3C2Tz; however, it is not clear
how altering the MXene type influences the resulting multilayer growth
and properties. Here, we report on the first use of MXenes other than
Ti3C2Tz, specifically
Ti2CTz and Nb2CTz, for the layer-by-layer (LbL) assembly of polycation/MXene
multilayers. By comparing these MXenes, we evaluate both how changing
M (Ti vs Nb) and “n”
(Ti3C2Tzvs Ti2CTz) affect the growth and properties
of the resulting multilayer. Specifically, the aqueous LbL assembly
of each MXene with poly(diallyldimethylammonium) into films and coatings
is examined. Further, we compare the oxidative stability, optoelectronic
properties (refractive index, absorption coefficient, optical conductivity,
and direct and indirect optical band gaps), and the radio frequency
heating response of each multilayer. We observe that MXene multilayers
with higher “n” are more electrically
conductive and oxidatively stable. We also demonstrate that Nb2CTz containing films have lower
optical band gaps and refractive indices at the cost of lower electrical
conductivities as compared to their Ti2CTz counterparts. Our work demonstrates that the properties
of MXene/polycation multilayers are highly dependent on the choice
of constituent MXene and that the MXene type can be altered to suit
specific applications.