Synthesis and Characterization of Carbon Quantum Dots from Saba (Musa acuminata× balbisiana) Banana Peel Waste: Effect of Maturity and Carbonization Temperature

Banana peels are considered one of the most abundant biowastes while Saba banana (Musa acuminata × balbisiana) is one of the most consumed fruit varieties in the Philippines. This research focused on the synthesis and characterization of carbon quantum dots (CQDs) from ripe and unripe Saba banana peels (SBP) via hydrothermal carbonization using low (100°C) and high (200°C) carbonization temperatures. Transmission electron microscopy revealed that ripe CQDs synthesized at these temperatures (rCQDs-100 and rCQDs-200, respectively) possessed disk-shaped and quasi-spherical structures with particle size range of 1.71-5.05 nm and 1.55-4.66 nm, respectively. However, unripe CQDs (uCQDs-100 and uCQDs-200, respectively) could not be considered as quantum dots due to their flake-like morphology and relatively large particle size (>40 nm and 2.21-21.24 nm, respectively). Likewise, Fourier-transform infrared spectroscopy identified the presence of enormous functional groups in all samples. Interestingly, C=N group was found only in uCQDs corresponding to the presence of chlorophyll in the samples. Moreover, all the CQDs emitted blue-green color under UV light illumination, with rCQDs-200 exhibited the best fluorescence emission. Thus, the approach of synthesizing CQDs using ripe SBP at higher temperature offers higher reacted precursors, better morphology, and greater fluorescence emission.