Nanoconfinement enabled non-covalently decorated MXene membranes for ion-sieving

'Covalent modification, while tuning the channel size and functionality, disrupts the structure of 2D membranes. Here the authors demonstrate controllable and selective mass transport, via nondisruptive non-covalent modification of sub-1-nm MXene channels, enabled by nanoconfinement effect. Covalent modification is commonly used to tune the channel size and functionality of 2D membranes. However, common synthesis strategies used to produce such modifications are known to disrupt the structure of the membranes. Herein, we report less intrusive yet equally effective non-covalent modifications on Ti3C2Tx MXene membranes by a solvent treatment, where the channels are robustly decorated by protic solvents via hydrogen bond network. The densely functionalized (-O, -F, -OH) Ti3C2Tx channel allows multiple hydrogen bond establishment and its sub-1-nm size induces a nanoconfinement effect to greatly strengthen these interactions by maintaining solvent-MXene distance and solvent orientation. In sub-1-nm ion sieving and separation, as-decorated membranes exhibit stable ion rejection, and proton-cation (H+/Mn+) selectivity that is up to 50 times and 30 times, respectively, higher than that of pristine membranes. It demonstrates the feasibility of non-covalent methods as a broad modification alternative for nanochannels integrated in energy-, resource- and environment-related applications.

Automated summary

The authors demonstrate controllable and selective mass transport through non-disruptive non-covalent modification of sub-1-nm MXene channels, enabled by nanoconfinement effect. Traditional covalent modification used to tune the size and functionality of 2D membranes often disrupts the membrane structure. However, in this study, non-intrusive non-covalent modifications on Ti3C2Tx MXene membranes were achieved by solvent treatment, resulting in densely functionalized channels decorated by protic solvents via hydrogen bond network. These as-decorated membranes exhibit stable ion rejection and enhanced proton-cation selectivity, making non-covalent methods a potential modification alternative for nanochannels in energy, resource, and environment-related applications.