Effect of surface termination on ion intercalation selectivity of bilayer Ti ₃ C ₂ T ₂ (T = F, O and OH) MXene

Using density functional theory (DFT) calculations we study the effect of surface functionalization on the response of bilayer Ti ₃ C ₂ T ₂ (T = F, O and OH) MXene to intercalating ions. In the case of pristine MXene, interlayer spacing (d) increases with introducing both anions and cations. The response of the system to the intercalating ions changes significantly after the surface functionalization: interlayer spacing increases in response to anions, whereas cation intercalation results in the contraction of d. The interplanar distance decreases further with increasing the charge state of the cations, the effect which becomes more pronounced in the case of Ti ₃ C ₂ O ₂ . Such dynamic response of the system to the intercalating ions is also confirmed in both DFT and ReaxFF force field-based molecular dynamics simulations. These results show the importance of surface functionalization to water applications of MXene.