Tuning surface properties of graphene oxide quantum dots by gamma-ray irradiation

Gamma-ray irradiation was employed to tune surface properties of graphene oxide quantum dots (GOQDs), such as functional groups and defect density. The GOQDs were first oxidized under gamma-ray irradiation with doses ranging from 0 to 200 kGy, and then reduced under larger irradiation doses from 200 to 400 kGy. In other words, both the defect density and the number of surface functional groups increased first and then decreased along with the increasing irradiation dose. This process was confirmed with UV-visible absorption, X-ray photoelectron spectroscopy, Raman spectra and Fourier transform infrared spectra. In order to estimate their pi-conjugated content, the GOQDs were served to quench the fluorescence of Rhodamine 6 G. The results showed that there existed a positive relationship between the pi-conjugated content and the static quenching coefficient VqNa, which might have a potential value. (C) 2016 Elsevier B.V. All rights reserved.