The role of oxygen defects in magnetic properties of gamma-irradiated reduced graphene oxide

Recently, graphene oxide and its unconventional magnetism have attracted much interest due to their novel applications in spintronics, memory chips and theranostics. Owing to the excellent biocompatibility, cellular uptake, bio-conjugation possibilities, flexible chemical modification and characteristic broad-wavelength absorbance, graphene oxide and its derivatives have been utilized as contrast agents for various imaging modalities such as photoluminescence, photoacoustic or ultrasound. Despite their suitable applications in bioimaging and due to lack of magnetic moment, graphene oxide cannot confer magnetic resonance imaging contrast without incorporating the magnetic component. Such compounds cannot change the magnetic characteristic of biological tissues as T-1 or T-2; therefore, emitted signal intensity of different tissues remains constant resulting in weak contrast. However, the possibility of improving its magnetic response by introducing defects or manipulating oxygen functionalities renders it an excellent candidate for magnetic resonance imaging contrast agents. In this work, graphene oxide was prepared in different oxidation conditions. Then, the oxides were reduced in hot distilled water. The resultant reduced graphene oxide was then irradiated by gamma rays at different doses of 25, 50, 75 and 100 kGy; and the effect of various oxygen-functional groups and structural defects induced by the release of oxygen or gamma ray on the magnetic properties of graphene oxide were investigated. The results revealed that the hydroxyl and epoxy groups play a prominent role in increasing the magnetization of graphene oxide due to induced quasi-localized state at graphene structure. The removal of oxygen functionalities during the reduction process leads to structural defects and distortions that are responsible for induced-magnetic moments. Considering the fact that oxygen functionalities influence the defects or distortions, the variation in magnetic behavior of graphene oxide was directly correlated to the density of defects and oxygen content. (C) 2019 Elsevier B.V. All rights reserved.