Optimisation of the quantum yield of carbon quantum dots prepared from bergamot pomace by means of a full factorial experimental design

Carbon Quantum Dots (CQDs) are versatile nanomaterials known for their tuneable optical properties and strong photoluminescence, making them suitable for potential use in various environmental and sensing applications. In this study, CQDs were synthesized via hydrothermal treatment of bergamot pomace, a citrus industry byproduct, in line with green chemistry and circular economy principles. A full factorial experimental design was employed to systematically optimize the quantum yield (Φ) by varying reaction time, temperature, and precursor concentration. The best model included positive linear parameters, interaction terms involving temperature and time, as well as the quadratic parameter for the precursor concentration. The quadratic parameters relative to time were found to be negative and indicated an optimised reaction time at ~ 9 h. The resulting CQDs were extensively characterized. UV-Vis absorption and fluorescence spectroscopy showed the typical CQD optical features with minor variations depending on the synthesis conditions. Raman spectroscopy revealed characteristic D and G bands and allowed for an estimation of the particle diameters (≤ 62.28 nm), while TEM measurements showed particle size up to 52.5 nm, with higher uniformity for lower reaction temperatures. DLS suggests the nanoparticle aggregation in aqueous solution, supported by HPLC which also revealed two distinct CQDs families. ATR-FTIR and potentiometric titrations indicate predominance of carboxylate groups on the product surface. Overall, this study presents a structured optimization strategy for enhancing CQD properties from renewable feedstocks and highlights their potential for future integration into environmental monitoring systems.