Synthesis and characterization of N-Carbon Quantum Dots (N-CQDs) via a simplified-facile hydrothermal method

Abdul Latif, Nurul Ayunni (2025) Synthesis and characterization of N-Carbon Quantum Dots (N-CQDs) via a simplified-facile hydrothermal method. Masters thesis, Universiti Teknikal Malaysia Melaka.

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Abstract

Carbon quantum dots (CQDs) are zero-dimensional nanomaterials celebrated for their exceptional chemical stability, water dispersibility, biocompatibility, and photoluminescence properties. This study explores the synthesis of nitrogen-doped carbon quantum dots (N-CQDs) using urea and citric acid derived from calamansi lime through an eco-friendly hydrothermal method. Synthesis parameters comprising of temperature, reaction time, and precursor ratio were systematically optimized using a 2³ full factorial Design of Experiment (DOE) across 11 experimental sets. Response Surface Methodology (RSM) and ANOVA analysis pinpointed optimal conditions at 140°C, a reaction time of 2 hours, and a precursor ratio of 1:1 (urea: citric acid), yielding N-CQDs with a maximum bandgap of 5.813 eV as determined by the Tauc plot. Extensive characterization of the synthesized N-CQDs was conducted using a suite of analytical techniques. UV-VIS spectroscopy revealed optical absorption properties and calculated bandgap values, while FTIR spectroscopy confirmed the integration of nitrogen and oxygen functional groups. Photoluminescence (PL) spectroscopy showcased intense luminescence, and Zeta potential analysis (-25 mV and -22.7 mV for sample 1 and sample 6) affirmed excellent colloidal stability. Structural and morphological analyses via FESEM, TEM, and EDX confirmed the N-CQDs' uniform spherical morphology with particle sizes ranging from 5 to 10 nm. EDX further validated the successful nitrogen doping through the presence of carbon, nitrogen, and oxygen elements. This study established a critical link between particle size, bandgap, and optical properties, governed by the quantum confinement effect. Smaller particles (e.g., 3.47 nm for Sample 1) exhibited higher bandgap values and minimal aggregation, while larger particles (e.g., 4.06 nm for sample 6) demonstrated reduced bandgap values and increased aggregation. The results underscore the dynamic surface chemistry and tunable characteristics imparted by nitrogen doping. In conclusion, the study successfully achieved its objectives by synthesizing N-CQDs with adjustable optical, electronic, and structural properties through a sustainable and efficient hydrothermal process. The integration of advanced analytical techniques provided profound insights into the surface, chemical, and morphological attributes of N-CQDs, highlighting their immense potential for diverse applications in bioimaging, sensing, and catalysis.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Quantum dots, Composites materials, Nanostructured materials, Nano electronics, Biocompatibility
Subjects:	T Technology > T Technology (General) T Technology > TK Electrical engineering. Electronics Nuclear engineering
Divisions:	Library > Tesis > FTKIP
Depositing User:	Norhairol Khalid
Date Deposited:	18 Aug 2026 08:05
Last Modified:	18 Aug 2026 08:05
URI:	http://eprints.utem.edu.my/id/eprint/30344
Statistic Details:	View Download Statistic

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