Quantifying hydroxyl radicals generated by a low-temperature plasma using coumarin: methodology and precautions.

The detection and quantification of hydroxyl radicals (HO˙) generated by low-temperature plasmas (LTPs) are crucial for understanding their role in diverse applications of plasma radiation. In this study, the formation of HO˙ in the irradiated aqueous phase is investigated at various plasma parameters, by probing them indirectly using the coumarin molecule. We propose a quantification methodology for these radicals, combining spectrophotometry to study the coumarin reaction with hydroxyl radicals and fluorimetry to evaluate the formation yield of the hydroxylated product, 7-hydroxycoumarin. Additionally, we thoroughly examine and discuss the impact of pH on this quantification process. This approach enhances our comprehension of HO˙ formation during LTP irradiation, adding valuable insights to plasma's biological applications.

New Insights into the Reactivity of Detonation Nanodiamonds during the First Stages of Graphitization.

The present study aims to compare the early stages of graphitization of the same DND source for two annealing atmospheres (primary vacuum, argon at atmospheric pressure) in an identical set-up. DND samples are finely characterized by a combination of complementary techniques (FTIR, Raman, XPS, HR-TEM) to highlight the induced modifications for temperature up to 1100 °C. The annealing atmosphere has a significant impact on the graphitization kinetics with a higher fraction of sp2-C formed under vacuum compared to argon for the same temperature. Whatever the annealing atmosphere, carbon hydrogen bonds are created at the DND surface during annealing according to FTIR. A "nano effect", specific to the <10 nm size of DND, exalts the extreme surface chemistry in XPS analysis. According to HR-TEM images, the graphitization is limited to the first outer shell even for DND annealed at 1100 °C under vacuum.