Fluorescence Enhancement and Radiolysis of Carbon Dots through Aqueous γ Radiation Chemistry

Low fluorescence quantum yields and possible impacts on environments are the issue of the newly emerging fluorescent carbon dots (CDs). In this study, we report on the gamma-irradiation effects on CDs in aqueous solutions. We found that CDs could be either easily decomposed to small molecules or enhanced in fluorescence quantum yields in selective aqueous gamma-irradiation systems. On one hand, CDs were more susceptible to gamma-irradiation than expected and could be decomposed by gamma-irradiation with the dosage of 15 kGy in pure water. On the other hand, CDs could be prevented from irradiation decomposition and the fluorescence of CDs could be dramatically enhanced if isopropanol was added to the aqueous irradiation systems. Isopropanol acted as a radical scavenger especially generating a reductive environment in irradiated aqueous solutions. Structure analysis showed that CDs irradiated in isopropanol solutions caused more reduced surface functional groups and less sp(3) defects of carbon structure than that of CDs irradiated in pure water. gamma-irradiation could be a simple and efficient approach either for fluorescence enhancement of CDs or for degradation of waste CDs on a large scale.