Gamma rays impact on 2D-MoS₂ in water solution

Two-dimensional transition metal dichalcogenides, particularly MoS₂, are interesting materials for many applications in aerospace research, radiation therapy and bioscience more in general. Since in many of these applications MoS₂-based nanomaterials can be placed in an aqueous environment while exposed to ionizing radiation, both experimental and theoretical studies of their behaviour under these conditions is particularly interesting. Here, we study the effects of tiny imparted doses of 511 keV photons to MoS₂ nanoflakes in water solution. To the best of our knowledge, this is the first study in which ionizing radiation on 2D-MoS₂ occurs in water. Interestingly, we find that, in addition to the direct interaction between high-energy photons and nanoflakes, reactive chemical species, generated by γ-photons induced radiolysis of water, come into play a relevant role. A radiation transport Monte Carlo simulation allowed determining the elements driving the morphological and spectroscopical changes of 2D-MoS₂, experimentally monitored by SEM microscopy, DLS, Raman and UV-vis spectroscopy, AFM, and X-ray photoelectron techniques. Our study demonstrates that radiolysis products affect the Molybdenum oxidation state, which is massively changed from the stable + 4 and + 6 states into the rarer and more unstable + 5. These findings will be relevant for radiation-based therapies and diagnostics in patients that are assuming drugs or contrast agents containing 2D-MoS₂ and for aerospace biomedical applications of 2DMs investigating their actions into living organisms on space station or satellites.