Synthesis of reduced graphene oxide quantum dots from graphene oxide via hydrothermal process and theirs structural, luminescence and magnetic properties

Background: Reduced graphene oxide quantum dots (rGO-QDs) have attracted much interest because of its exceptional chemical and physical properties and novel applications in a new technology and devices such as, energy storage, electrochemical, photocatalysis, sensing, drug delivery, bioimaging and anticancer therapy. Methods: In this work, we reported a correlation study of the structural, morphological, luminescence and magnetic behavior of rGO-QDs as a function of hydrothermal reduction temperatures (such as 90 degrees C, 120 degrees C, 150 degrees C and 180 degrees C) of GO sheets precursor via hydrothermal process. GO precursor and the obtained rGO-QDs samples were confirmed and analyzed by several techniques such as, XRD, Raman, XPS, TEM, PL, UV-Visible, Fluorescence and EPR. Significant findings: Influence of hydrothermal cutting process with different temperatures (90 degrees C, 120 degrees C, 150 degrees C and 180 degrees C) on the evolution of structural, morphologies, luminescence and magnetic behavior for the changes of large GO sheets into ultra-small rGO-QDs is presented. XRD result confirmed the effect of increasing temperature on the hydrothermal cutting process which led to a decrease in D-spacing values of rGO-QDs products. While Raman results indicates the trend of ID/IG ratio decreases along with increasing hydrothermal reduction temperatures. XRS analysis revealed that the percentage of carbon content of GO precursor (-64%) was shifted value to -83% for obtained rGO-QDs sample prepared at 180 degrees C. TEM images shown that a very thin plate-like shape with ultrasmall average diameter of rGO-QDs samples in rage of 22 +/- 2 nm to 8 +/- 2 nm. The optical and PL results well-confirmed the characteristic quantum size effect of all rGO-QDs samples. Finally, the EPR signals indicate the crossover between paramagnetic and diamagnetic are depended on the reduction temperature. The rGO-QDs prepared at 180 degrees C do not give any EPR signal, signify the nonmagnetic nature. This indicate that the basal plane of rGO-QDs at 180 degrees C has nearly perfect sp2 network of graphene.