Experimental and numerical investigations on the transport mechanisms of Ti₃C₂T_x MXene under variable flow and...

Ti₃C₂T_x can be released into the groundwater environment due to its widespread application. It poses a severe environmental risk due to its cytotoxicity but has received little attention. In the groundwater, the dynamic groundwater flow and solution chemistry will affect the transport behavior of Ti₃C₂T_x which is still unclear and necessary for the assessment of its environmental impact. Thus, this study investigated the influential mechanisms of groundwater flow and solution chemistry on the transport of Ti₃C₂T_x by considering its 2D shape and degradation characteristics via column experiments with numerical models. The results showed that the transport of Ti₃C₂T_x in the quartz sand column significantly increased with the decrease of ionic strength (IS) and increase of pH and sodium humate. Face-on oriented Ti₃C₂T_x particles were reversibly attracted in the secondary minimum, whereas edge-on orientation favored the irreversible attachment in the primary minimum that was facilitated by the nanoscale charge heterogeneity. The retention of Ti₃C₂T_x significantly increased during the FI period due to the enhanced residence time, facilitating edge-on attachment by diffusion and diffusion into stagnation zones. This study demonstrated the controlling roles of the shape and degradation characteristics of Ti₃C₂T_x on its mobility, suggesting that such unique properties should be considered in assessing the environmental fate of emerging nanoparticles.