The Impact of Metal Ions on MXene Membranes: Critical Role of Titanium Vacancies

Two-dimensional transition metal carbides and nitrides (MXenes) and MXene-based membranes hold promise for applications including water purification and seawater desalination; however, their environmental behavior and fate in these matrices remain unknown. In this study, we systematically assessed the reaction efficiencies of Ti3C2Tx at varying important environmental conditions. Our experiments revealed that copper and iron ions accelerated the oxidation rate of Ti3C2Tx 55.4 and 33.4 times, respectively. TiO2 and amorphous carbon were identified as the primary solid products. Based on in situ water-phase atomic force microscopy, atomic high-angle annular dark-field scanning transmission electron microscopy, and theoretical results, we postulate that metal ions enhance Ti3C2Tx oxidation by spontaneously migrating and anchoring at Ti vacancies, which then become active sites for this reaction. This process increases the adsorption of H2O and oxygen, making the Ti vacancy-rich surface convex area the most vulnerable site to attack. The findings in this study provide useful information for a comprehensive understanding of the interaction between MXene structural defects and metal ions as well as for the design and modification of MXene membranes resistant to metal ion impact.