Strongly Modulated Exfoliation and Functionalization of MXenes with Rationally Designed Groups in Polymer: A Theoretical Study

As emerging atomically ultrathin metal compounds, MXenes show great promise for catalytic and nanoelectronic applications due to their abundant surface terminations and high metallic conductivity. However, the tendency for 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 MXenes via polymers, which have been experimentally proven to promote the performance. Nine kinds of monomers together with a typical MXene, Ti3C2T2 (T = none, O, F, OH, F-0.5, O-0.5), as prototype composites are explored with respect to the adsorption and charge transfer associated with energetics and chemical redox, respectively. Our work shows that the naked Ti3C2 MXene has 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 polymers would alter the carriers' density via interfacial charge transfer in MXenes. While the naked Ti3C2 and Ti3C2(OH)(2) donate electrons to the polymers, Ti3C2F2, Ti3C2FO, and Ti3C2O2 receive small amounts of electrons transferred from the polymer, highly depending on the types of the monomers. The varying ability for charge transfer and exfoliation energy of different monomers imply great flexibility for designing polymers to exfoliate the MXene and modulate the carrier densities, which are highly desired for altering the conductivity, dielectric properties, and promoting endurance.

Automated summary

MXenes, as promising materials for catalytic and nanoelectronic applications, have limitations in interlayer adhesion and environmental disturbances. This study explores the surface passivation and exfoliation of MXenes through polymers, revealing the effects of different monomers on adsorption and charge transfer. The results show that specific functional groups and polymer types have significant effects on the properties of MXenes.