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

Abstract

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.

Organic Functionalization of Ti3C2Tx MXene for Urea Adsorption in Aqueous Solutions

“…Ion exchange or surface functionalization of MXene can be used to remove the intercalated Li + ions, which in turn improves the urea adsorption energies for MXene. Functionalizing the surface with Cu significantly enhances the urea adsorption capability of this material, provided the Cu loading is sufficiently low so that Cu is evenly dispersed across the surface . This result was supported by DFT calculations, which showed that the formation of the Ti–O–Cu linkage increases the binding energy of urea to the surface .…”

“…Compared to the Glu MXene system, the Cu-functionalized Glu MXene (Cu 39.3 Glu MXene) exhibits additional paramagnetic influences from surface Cu 0 ions, particularly on the secondary and tertiary carbons, while the carboxylic acid remains relatively unaffected (Figure a,b). While Cu + is diamagnetic and should not contribute to paramagnetic influences in the NMR spectrum, our previous study revealed that Cu-functionalization results in Cu oxidation states between 0 and 1 . Cu 0 is paramagnetic and is thought to contribute to the paramagnetic broadening/shifting as well as the Ti 3+ ions.…”

“…Recent work has revealed how Cu functionalization of the Ti 3 C 2 T x surface significantly enhances its urea adsorption properties . This improvement in adsorption properties was shown by DFT calculations to be the result of larger binding energies of urea to the surface functionalized with Cu, compared to a Li + intercalated surface dominated by −OH and −F terminations .…”

“…The method was adapted and modified from Lam et al Ti 3 C 2 T x (250 mg) was sonicated in DI water (250 mL) for 10 min. 6.7 mL of CuCl 2 (1 mg/mL) was added into the Ti 3 C 2 T x suspension.…”