A chemometric approach for the optimization of the synthesis of biomass-based Carbon Quantum Dots

Since the discovery of Carbon Quantum Dots (CQDs) in 2004,1 interest in these materials has increased over the last two decades. Moreover, the synthesis of CQDs from green sources offers a valuable alternative for waste management and has received great attention thanks to the biocompatibility and affordability of the starting materials.2 Among the various preparation strategies, the most common is the green hydrothermal method. However, the literature varies widely on the chosen synthesis conditions. For the hydrothermal treatment using water as solvent, temperature, time, and initial concentration of precursors seem to be the main parameters affecting the properties of the obtained products in terms of particle size and surface functionalization, which in turn reflect on the photoluminescence properties and stability of the CQDs.3 This work exploits the chemometric tool of experimental design4 to optimize the synthesis of biomass-based CQDs. Citrus waste lyophilized bergamot pomace was used as a precursor. An initial hydrothermal synthesis was performed using 250 mg of pomace in 25 mL of water, heated in an autoclave at 180 °C for 6 hours.5 The experimental design was then conducted according to a 2k full factorial design while varying the initial amount of precursor (200 and 300 mg of pomace), the temperature (150 and 210 °C), and the reaction time (3 and 6 hours). After purification, the quantum yield was evaluated using quinine sulfate as a reference, and the particle size was evaluated through Transmission Electron Microscopy. The results were used to construct the experimental surface, allowing to determine the optimal conditions for the synthesis of CQDs from bergamot pomace and to clarify which parameter mostly influences the properties of the obtained product. Aknowledgement: We thank MUR: PNRR - Missione 4, Componente 2, Investimento 1.1 - Bando Prin 2022 - Decreto Direttoriale n. 104 del 02-02-2022. Project title: “Wastezilla: Recycled waste biomass for efficient recovery of critical elements”. CUP: J53D23007540006 – project code: PRIN_2022HYH95P_001. References: [1] X. Xu, R. Ray, Y. Gu, H. J. Ploehn, L. Gearheart, K. Raker, W.A. Scrivens, J. Am. Chem. Soc. 2004, 40, 12736–12737. [2] S. Mathew, B. Mathew, Inorg. Chem. Commun. 2023, 156, 111223. [3] M. Palacio-Vergara, M. Álvarez-Gómez, J. Gallego, D. López, Talanta Open 2023, 8, 100244. [4] R. Leardi, Anal. Chim. Acta 2009, 1, 161–172. [5] Z. Wang, Y. Xie, Z. Lei, Y. Lu, G. Wei, S. Liu, C. Xu, Z. Zhang, X. Wang, L. Rao, Anal. Chem. 2019, 15, 9690–9697.