Sustainable biomass-derived graphene quantum dots from pomegranate peels for supercapacitor applications

Abstract

Abstract Using pomegranate peel as the sole precursor, we report a facile, one-pot hydrothermal synthesis of size-tunable graphene quantum dots (GQDs), emphasizing the tunability and functional stability of the dots without requiring surface passivation agents. As the synthesis temperature increases, the dot size decreases from 16.52 to 9.57 nm. This temperature-dependent size evolution is correlated with changes in fluorescence emission, colloidal stability, oxygen-containing surface groups, and capacitive response, providing a structure–property link for pomegranate-peel-derived GQDs. The fluorescence spectra show excitation-dependent behavior with the 200 °C sample showing the maximum emission peak upon excitation with 360 nm wavelength of light. We achieve a fluorescence quantum yield of ∼3.6% with a fluorescence decay time of approximately 2.4 ns. All samples display relatively stable colloidal properties. The GQDs synthesized at 200 °C were evaluated as sustainable nanoscale additives on laser-induced graphene electrodes, achieving an areal capacitance of 2.07 mF cm −2 at 7.5 μ A cm −2 . Although the performance is modest compared with optimized carbon-based supercapacitors, the results demonstrate that biomass-derived GQDs can serve as a sustainable material for energy-storage applications.