Colloidal Behaviors of Two-Dimensional Titanium Carbide in Natural Surface Waters: The Role of Solution Chemistry.

Although two-dimensional titanium carbide (TiCT MXene) has emerged as a shining star material in various communities, its environmental behaviors and fate remain unknown. Herein, the colloidal properties and stability of TiCT MXene are explored in aquatic systems for the first time, considering the roles of solution chemistry conditions (e.g., pH, ionic types, and strength). It was found that pH had no effect on the stability of TiCT in the range of 5.0-11.0, whereas ionic valence and concentrations displayed significant effects on the aggregation behavior of TiCT. By employing time-resolved dynamic light scattering measurements, the critical coagulation concentration (CCC) value of TiCT was determined to be 12 mM for NaCl. The divalent cations Ca and Mg exhibited higher destabilizing capacity to TiCT, as evidenced by the lower CCC values (0.3 and 0.4 mM for CaCl and MgCl, respectively) and faster coagulation rates. Long-term stability studies implied that TiCT MXene was less likely to be transported over long distances in the synthetic or natural waters. These findings provided significant insights into the fate and transport of TiCT in the aquatic environment.