Understanding the Termination Effect of Ti3C2TX MXene Membrane on Water Structure and Interaction with Alginate Foulants: A Molecular Dynamics Study

The effects of termination functional groups of the Ti3C2Tx MXene membrane on the structural and dynamics properties of nearby water molecules and foulants are investigated through molecular dynamics simulations. The simulation results show that a much denser water layer can be formed at the vicinity of hydroxyl (OH) termination than that near fluorine (F) or oxygen (O) termination. Particular focus is given to the molecular binding properties of β-d-mannuronic acid (M) and α-l-guluronic acid (G) alginate monomers on the MXene membrane surface with different termination groups. Further steered molecular dynamics (SMD) simulations show that M alginate monomers exhibit significant binding with the MXene membrane surface with O termination, due to the strong electrostatic interaction and the van der Waals attraction. In contrast, the binding between the alginate monomers and the MXene membrane surface with OH termination is negligible, as the stable hydration water network prevents them from direct contact. In addition, SMD simulation results show that calcium (Ca2+) ions could significantly enhance the surface fouling between M alginate monomers and the MXene with an O termination through the formation of contact ionic pair (CIP) and solvent-shared ionic pair (SSIP) structures.