Biomass-derived surface-functionalized graphene quantum dots for aggregation-induced green fluorescence

In the realm of nanomaterials, surface modification and vacancy defects are widely recognized as key factors that influence various physical and chemical properties. However, the creation and dynamic structural evolution of vacancy defects in atomically thin graphene quantum dots (GQDs) remain largely unexplored, primarily due to the challenges in isolating GQDs that exhibit such defects. In this study, nitrogen-doped GQDs (size ca. 3 nm) were synthesized from biomass extracts and subsequently surface functionalized to enhance their properties. Interestingly, the functionalization process not only introduced inner defects but also promoted the aggregation of GQDs, which, in turn, led to a significant boost of green fluorescence. The successful synthesis of GQDs and the incorporation of functional groups were confirmed using various characterization techniques. UV-vis spectroscopy was employed to identify the characteristic optical signatures of GQDs, while FTIR spectroscopy verified the presence of specific functional groups. Dark-field scanning transmission electron microscopy (STEM) was utilized for size authentication, visualization of inner defects, and insights into the morphological features of the GQDs. X-ray photoelectron spectroscopy was employed for elemental analysis. Additionally, luminescence studies, including fluorescence and photoluminescence, were conducted to investigate the optical properties. The meticulously prepared surface-functionalized GQDs, showcasing elevated luminescence, hold significant promise as advanced multifunctional materials. Their semiconducting nature makes them strong candidates for high-performance display applications, while their exceptional biocompatibility and robust fluorescence position them as an ideal platform for drug delivery, particularly in cancer therapeutics.