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MXenes are a newer class of 2D materials, possess with desirable properties such as large specific surface area, conductivity, and hydrophilicity, making them attractive for various environmental applications, including remediation and as membranes for water treatment. Until recently, the practical implementation of MXenes was hindered by their instability in water, although improved synthesis procedures have largely addressed this issue. Consequently, it is now important to assess the stability of MXenes in engineered environments relevant to drinking water and membrane operation (e.g. backwashing). In this study, Ti3C2Tx MXenes were found to remain stable upon exposure to an aqueous environment saturated with oxygen and to UVC and UVA light at circumneutral pH, but were transformed upon exposure to Fe(III) chloride and free chlorine. The chlorination reaction kinetics are 1st order with respect to Ti3C2Tx and free chlorine concentration, with a rate constant that increased at pH ≤ 7.5, implicating HOCl as the reactive species. We propose that MXene reactions with HOCl occur by an electrophilic attack of Cl+, forming TiO2 and degrading the MXene. AFM data shows that transformations are initiated at the edges of the MXene sheets and localized areas on the MXene, suggesting that the initial sites for Cl+ attack are defect sites and/or uncoordinated Ti atoms. During the initial stages of the oxidative degradation, the sheet-like structure of colloidal MXenes is preserved, although prolonged chlorine exposure leads to three-dimensional crystalline (anatase) TiO2 formation. The degradation of MXenes during chlorinationThis contrasts with the inertness of nanoscale TiC, highlighting the need to devise surface modification processes that will allow MXenes to resist the oxidative conditions associated with membrane regeneration/backwashing.
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This content will become publicly available on October 28, 2026
Defect-Driven Degradation of MXenes in Aqueous Environments and Mitigation Strategies: Insights from First-Principles
MXenes have attracted considerable attention due to their tunable surface chemistry, high electrical conductivity, and ease of solution processing, making them promising candidates for a wide array of applications. The inherent tendency of MXenes to degrade under environmental conditions constrains their compositional diversity and limits certain practical applications. Our computational study shows that degradation of defect-free Ti3C2Tx is kinetically limited, whereas common defects markedly lower the activation barriers for water attack. Using ab initio molecular dynamics simulations (AIMD) combined with thermodynamic analysis, we show that titanium vacancies VTi act as active sites for the protonation of subsurface carbon atoms, weakening the bonds with and accelerating the release of adjacent Ti atoms. Targeted passivation of these sites by adsorbed metal cations (e.g., Li+, Na+, K+, and Mg2+) is predicted to effectively mitigate degradation by suppressing protonation and increasing the barrier for Ti oxidation. This stabilization arises from two synergistic effects: (i) electronic structure modification driven by a strong dipole moment, which markedly shifts the work function, and (ii) steric hindrance that limits water access to reactive defect sites. We also demonstrate that carbon vacancies VC significantly destabilize adjacent Ti atoms, lowering the energy barrier for the water attack reaction. The substitution of VC with electronegative species such as O or N does not significantly improve the stability of Ti3C2Tx, highlighting the detrimental role of any defects in the carbon sublattice. Because VC are typically inherited from the precursor phase and cannot be removed during postsynthesis, controlling their concentration during Mn+1AXn phases synthesis is essential. Our thermodynamic analysis reveals that A-rich (e.g., Al-rich) synthesis conditions substantially increase the formation energy of VC and VN defects in a large spectrum of Mn+1AXn phases, providing a generalizable strategy for defect suppression and improved durability of the resulting MXenes.
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- Award ID(s):
- 2324156
- PAR ID:
- 10645297
- Publisher / Repository:
- ACS
- Date Published:
- Journal Name:
- ACS Nano
- Volume:
- 19
- Issue:
- 42
- ISSN:
- 1936-0851
- Page Range / eLocation ID:
- 36994 to 37003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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