MXene Nanosheets Functionalized with Cu Atoms for Urea Adsorption in Aqueous Media

Ti₃C₂T_x MXene is an emerging family of two-dimensional materials, and because of its large specific surface area, it has the potential for many applications. Herein, a new application using Cu-doped MILD (minimally intensive layer delamination)-synthesized Ti₃C₂T_x MXene for urea removal is demonstrated. The doping of Cu on MXene results in an increase in its affinity for urea adsorption as compared to pristine MILD-synthesized MXene due to the formation of the Cu-urea complex. Previous computational studies have shown that the adsorption energies of urea on the MXene surface can be improved in the presence of Cu. The valence state of Cu in doped MILD-synthesized MXene, which binds onto the surface via a Ti-O-Cu linkage, is between 0 and +1, as verified by XAS and XPS. As the optimal urea adsorption occurs on Cu as a single-atom site, an increase in Cu doping on MXene does not increase urea removal due to Cu agglomeration. Looking at the adsorption behavior, it seems that Cu-doped MXene follows the monolayer adsorption on a homogeneous surface model.