SOLVOTHERMAL SYNTHESIS OF HIGHLY LUMINESCENT GRAPHENE QUANTUM DOTS FROM GRAPHENE OXIDE FOR DUAL APPLICATIONS IN COPPER ION SENSING AND NANOTHERMOMETRY

This research effectively produced graphene quantum dots (GQDs) utilizing a solvothermal method from graphene oxide (GO) with N, N-dimethylformamide (DMF) as the solvent. Transmission Electron Microscopy (TEM) analyses revealed that the produced GQDs primarily exhibited a spherical morphology, with uniformly distributed nanoparticles and a mean diameter of 4.12 nm. Photoluminescence (PL) studies show excitation-dependent green emission characteristics, with an emission wavelength of 551 nm under 500 nm excitation. This is associated with a high PL intensity and a quantum yield (QY) of 51.56%. X-ray diffraction (XRD) results confirmed that the GQDs have a graphitic structure. Fourier Transform Infrared Spectroscopy (FTIR) and Energy-Dispersive X-ray spectroscopy (EDX) confirmed the presence of oxygen functional groups, with carbon, oxygen, and nitrogen as the primary elemental components, verifying the nitrogen doping of the GQDs. The absence of other metals shows that the synthesized GQDs have a high level of purity. The synthesized GQDs were successfully utilized as an ion sensor for detecting Cu2+ ions, highlighting their exceptional sensitivity and selectivity with a limit of detection of 0.55 µm. The GQDs also exhibit potential nanothermometric behavior, as they display a photoluminescence response that depends on temperature with a sensitivity of 1.81% °C-1 between 20 °C and 70 °C. By combining nitrogen doping with a simple solvothermal synthesis, this research produces dual-function GQDs that enable both highly sensitive detection of Cu2+ ions and reliable temperature sensing.