A comparative study of structural stability, electronic, and spectroscopic properties of Carbon Quantum Dots (CQDs): a dual experimental/theoretical approach

Carbon Quantum Dots (CQDs) have garnered significant interest for their diverse applications, ranging from optoelectronic devices to biomedical imaging, owing to their unique electronic and optical properties. In this study, we present a comprehensive investigation into the synthesis, characterization, and computational analysis of CQDs derived from Watermelon seeds, focusing on the influence of defects on their properties. Initially, CQDs were synthesized using a green hydrothermal process with Watermelon seeds of varying maturity levels as precursors. Extensive characterization using UV-Vis, Raman spectroscopy, FTIR, and XPS techniques confirmed the successful synthesis and revealed crucial structural and chemical information about the CQDs, including the presence of functional groups such as amine, carboxyl, and carbonyl. Subsequently, employing Density Functional Theory (DFT), we analyzed the impact of different types of defects (edge, surface, and Stone-Wales) on the electronic, structural, and optical properties of CQDs. Our computational analysis unveiled intricate details about the electronic structure of CQDs, including the localization of orbitals at the edges for zigzag structures and delocalized orbitals for armchair structures. Furthermore, we observed significant changes in the bandgap and frontier molecular orbitals due to the presence of defects, indicating their crucial role in modulating the properties of CQDs. Surface defects, arising from experimentally found functional groups, were found to induce modifications in the electronic structure, resulting in a decrease in the bandgap and localization of states around the functional groups. Structural analysis revealed discrepancies between theoretical predictions and experimental observations, highlighting the need for further refinement in computational models. Similarly, CQDs modified with Stone-Wales defects exhibited altered electronic and structural properties, with a decrease in the bandgap and localization of orbitals around the defects. Structural analysis revealed the appearance of new peaks in FTIR spectra and a reduction in the intensity of certain Raman bands, indicating structural modifications induced by the defects. While our study provides valuable insights into the influence of defects on CQD properties, further research is warranted to fully understand their implications. By elucidating the role of defects in shaping the properties of CQDs, this research contributes to the development of novel carbon-based materials with tailored functionalities for diverse applications.

• 1. Verfasser: Lara Vera, David Daniel (author)
• Format: bachelorThesis
• Sprache: eng
• Veröffentlicht: 2024
• Schlagworte: Puntos Cuánticos de Carbono; Método hidrotermal; Teoría del Funcional de Densidad; Carbon Quantum Dots; Hydrothermal method; Density Functional Theory
• Online Zugang: http://repositorio.yachaytech.edu.ec/handle/123456789/806