Dimensionality-Driven Carbon Reconstruction Activates MXene Quantum Dots for Dechlorination

Two-dimensional MXenes have attracted significant interest as catalysts for environmental remediation. Yet, the most abundant oxygen-terminated MXenes exhibit limited reactivity toward chlorinated hydrocarbons. The influence of dimensionality on the reactivity of ${\mathrm{Ti}}_2{\mathrm{CO}}_2$ MXene nanostructures toward trichloroethylene (TCE) dechlorination is investigated using density functional theory. Reduction of ${\mathrm{Ti}}_2{\mathrm{CO}}_2$ from an extended two-dimensional surface to finite nanostructures substantially lowers the energetic cost of C-Cl bond cleavage, indicating that dimensional confinement and edge effects weaken the intrinsic inertness of the material. Partially terminated edges provide highly reactive sites where dechlorination proceeds with negligible activation barriers. An additional activation mechanism specific to finite MXene quantum dots is identified. Structural relaxation induces a local reconstruction of the carbon sublattice, forming a triangular carbon motif that redistributes electronic charge and introduces states near the Fermi level. These states facilitate charge transfer to the adsorbed molecule, lowering the activation barrier and stabilizing the dissociated products. These results reveal a previously unexplored pathway for activating otherwise weakly reactive MXenes at the nanoscale.