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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. 

Ion beam-induced deposition (IBID) using Pt(CO)₂Cl₂and Pt(CO)₂Br₂as precursors has been studied with ultrahigh-vacuum (UHV) surface science techniques to provide insights into the elementary reaction steps involved in deposition, complemented by analysis of deposits formed under steady-state conditions. X-ray photoelectron spectroscopy (XPS) and mass spectrometry data from monolayer thick films of Pt(CO)₂Cl₂and Pt(CO)₂Br₂exposed to 3 keV Ar⁺, He⁺, and H₂⁺ions indicate that deposition is initiated by the desorption of both CO ligands, a process ascribed to momentum transfer from the incident ion to adsorbed precursor molecules. This precursor decomposition step is accompanied by a decrease in the oxidation state of the Pt(II) atoms and, in IBID, represents the elementary reaction step that converts the molecular precursor into an involatile PtX₂species. Upon further ion irradiation these PtCl₂or PtBr₂species experience ion-induced sputtering. The difference between halogen and Pt sputter rates leads to a critical ion dose at which only Pt remains in the film. A comparison of the different ion/precursor combinations studied revealed that this sequence of elementary reaction steps is invariant, although the rates of CO desorption and subsequent physical sputtering were greatest for the heaviest (Ar⁺) ions. The ability of IBID to produce pure Pt films was confirmed by AES and XPS analysis of thin film deposits created by Ar⁺/Pt(CO)₂Cl₂, demonstrating the ability of data acquired from fundamental UHV surface science studies to provide insights that can be used to better understand the interactions between ions and precursors during IBID from inorganic precursors.