MXenes are a newer class of 2D materials with desirable properties, 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 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, Ti₃C₂T_x 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 excess free chlorine and to Fe(III) chloride at a concentration equal to 5 mg L⁻¹ free chlorine. The chlorination reaction kinetics are 1st order with respect to Ti₃C₂T_x and free chlorine concentration from 20 to 200 mg L⁻¹. The rate constant 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 show 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. This 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.

Next generation displays and lighting applications are increasingly using inorganic quantum dots (QDs) embedded in polymer matrices to impart bright and tunable emission properties. The toxicity of some heavy metals present in commercial QDs (e.g. cadmium) has, however, raised concerns about the potential for QDs embedded in polymer matrices to be released during the manufacture, use, and end-of-life phases of the material. One important potential release scenario that polymer composites can experience in the environment is photochemically induced matrix degradation. This process is not well understood at the molecular level. To study this process, the effect of an artificially accelerated weathering process on QD–polymer nanocomposites has been explored by subjecting CdSe and CdSe/ZnS QDs embedded in poly(methyl methacrylate) (PMMA) to UVC irradiation in aqueous media. Significant matrix degradation of QD–PMMA was observed along with measurable mass loss, yellowing of the nanocomposites, and a loss of QD fluorescence. While ICP-MS identified the release of ions, confocal laser scanning microscopy and dark-field hyperspectral imaging were shown to be effective analytical techniques for revealing that QD-containing polymer fragments were also released into aqueous media due to matrix degradation. Viability experiments, which were conducted with Shewanella oneidensis MR-1, showed a statistically significant decrease in bacterial viability when the bacteria were exposed to highly degraded QD-containing polymer fragments. Results from this study highlight the need to quantify not only the extent of nanoparticle release from a polymer nanocomposite but also to determine the form of the released nanoparticles (e.g. ions or polymer fragments).