  As emerging atomically ultrathin metal compounds, MXenes show great promise
for catalysts and nanoelectronics applications due to the abundant surface
terminations and high metallic conductivity. However, the tendency of the
interlayer adhesion and suffering from environmental disturbances significantly
limit their endurance and efficiency. Herein via conducting first-principles
calculations, we explore surface passivation and exfoliation of MXene via
polymers which have been experimentally proven to promote the performance. Nine
kinds of monomers together with the typical MXene Ti3C2T2 (T= None, O, F, OH,
F0.5O0.5) as prototype composites are explored with respect to the adsorption
and charge transfer associated with energetics and chemical redox,
respectively. Our work shows that naked Ti3C2 MXene has a strong ability to
cleave and decompose the monomers. Surface functionalized Ti3C2F2, Ti3C2FO, and
Ti3C2O2 have a weak binding with monomers through only van der Waals force,
whereas Ti3C2(OH)2 also exhibits strengthened binding for some monomers.
Specific functional groups in the monomer, such as the halogen, sulfur, and
hydroxyl groups or a relatively planar aromatic structure, largely contribute
to the adsorption. We reveal that the functionalization through polymer would
alter the carriers' density via interfacial charge transfer in MXenes. While
the naked Ti3C2 and Ti3C2(OH)2 donate electrons to the polymers, the Ti3C2F2,
Ti3C2FO, and Ti3C2O2 receive small amounts of electrons transferred from the
polymer, highly depending on the types of the monomers. The varying ability of
charge transfer and exfoliation energy of different monomers implies great
flexibility for designing polymers to exfoliate the MXene and modulate the
carrier densities which is highly desired for altering conductivity, dielectric
properties, and promoted endurance.
