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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. 

Supported lipid bilayers are often used as model systems for studying interactions of biological membranes with protein or nanoparticles. A supported lipid bilayer is a phospholipid bilayer built on a solid substrate. The latter is typically made of silica or a metal oxide due to the ease of its formation and range of compatible measurement techniques. Recently, a solvent-assisted method involving supported lipid bilayer formation has allowed the extension of compatible substrate materials to include noble metals such as gold. Here, we examine the influence of substrate composition (SiO2 vs Au) on the interactions between anionic ligand-coated Au nanoparticles or cytochrome c and zwitterionic supported lipid bilayers using quartz crystal microbalance with dissipation monitoring. We find that anionic nanoparticles and cytochrome c have higher adsorption to bilayers formed on Au relative to those on SiO2 substrates. We examine the substrate-dependence of nanoparticle adsorption with DLVO theory and all-atom simulations, and find that the stronger attractive van der Waals and weaker repulsive electrostatic forces between anionic nanoparticles and Au substrates vs anionic nanoparticles and SiO2 substrates could be responsible for the change in adsorption observed. Our results also indicate that the underlying substrate material influences the degree to which nanoscale analytes interact with supported lipid bilayers; therefore, interpretation of the supported lipid bilayer model system should be conducted with understanding of support properties.