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Sousa DA, Berberan-Santos MN, Prata JV. Are "Carbon Dots" Always Carbon Dots? Evidence for their Supramolecular Nature from Structural and Dynamic Studies in Solution and in the Pure Solid. Chemistry 2024; 30:e202302955. [PMID: 37943001 DOI: 10.1002/chem.202302955] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 11/06/2023] [Accepted: 11/08/2023] [Indexed: 11/10/2023]
Abstract
A model for the morphology (size, shape, and crystallinity) of carbon dots (CDs) in the solid state consistent with the observed photoluminescence in solution is proposed herein. Overwhelming evidence has been collected that links the data coming from solid-state analysis (high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS)) to that of solution (pulsed-field gradient (PFG)-NMR spectroscopy, time-resolved fluorescence anisotropy (TRFA), and steady-state/time-resolved fluorescence), allowing the establishment of an overall structural model for CDs. According to this model, the so-called carbon dots, observed under HRTEM imaging, are in fact supramolecular organized structures dynamically assembled from small to medium-sized molecular species when the solvent is removed to give the solid form. In this way, the imaged nanoparticles (TEM/AFM) are not covalently bound entities formed during the synthetic process, but instead supramolecular entities formed by noncovalent interactions. These particles, if at all present in solution, have the form of loose associations of relatively small molecules. This study was conducted on CDs obtained from the hydrothermal carbonization (HTC) of a biomass waste (olive wet pomace).
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Affiliation(s)
- Diogo A Sousa
- Department of Chemical Engineering Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa, 1959-007, Lisbon, Portugal
- BSIRG-iBB-Institute for Bioengineering and Biosciences, and Associate Laboratory i4HB - Institute for Health and Bioeconomy Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal
| | - Mário N Berberan-Santos
- BSIRG-iBB-Institute for Bioengineering and Biosciences, and Associate Laboratory i4HB - Institute for Health and Bioeconomy Instituto Superior Técnico, Universidade de Lisboa, 1049-001, Lisbon, Portugal
| | - José V Prata
- Department of Chemical Engineering Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa, 1959-007, Lisbon, Portugal
- CQ-VR-Centro de Química-Vila Real, Universidade de Trás-os-Montes e Alto Douro, 5001-801, Vila Real, Portugal
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Xu C, Xiao X, Cai C, Cheng Q, Zhu L, Zhang J, Wei B, Wang H. Insight into the differences in carbon dots prepared from fish scales using conventional hydrothermal and microwave methods. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2023; 30:54616-54627. [PMID: 36881236 DOI: 10.1007/s11356-023-26275-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Accepted: 02/28/2023] [Indexed: 06/18/2023]
Abstract
The preparation of carbon dots (CDs) from waste fish scales is an attractive and high-value transformation. In this study, fish scales were used as a precursor to prepare CDs, and the effects of hydrothermal and microwave methods on their fluorescence properties and structures were evaluated. The microwave method was more conducive to the self-doping of nitrogen due to rapid and uniform heating. However, the low temperature associated with the microwave method resulted in insufficient dissolution of the organic matter in the fish scales, resulting in incomplete dehydration and condensation and the formation of nanosheet-like CDs, whose emission behavior had no significant correlation with excitation. Although the CDs prepared using the conventional hydrothermal method showed lower nitrogen doping, the relative pyrrolic nitrogen content was higher, which was beneficial in improving their quantum yield. Additionally, the controllable high temperature and sealed environment used in the conventional hydrothermal method promoted dehydration and condensation of the organic matter in the fish scales to form CDs with a higher degree of carbonization, uniform size, and higher C = O/COOH content. CDs prepared using the conventional hydrothermal method exhibited higher quantum yields and excitation wavelength-dependent emission behavior.
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Affiliation(s)
- Chengzhi Xu
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China
| | - Xiao Xiao
- School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, Hubei, China
| | - Chaonan Cai
- School of Food Science and Engineering, Wuhan Polytechnic University, Wuhan, Hubei, China
| | - Qunpeng Cheng
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China
| | - Lian Zhu
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China
- School of Chemistry and Environmental Engineering, Hubei Minzu University, Enshi, Hubei, China
| | - Juntao Zhang
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China
| | - Benmei Wei
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China
| | - Haibo Wang
- School of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Changqing Garden, Wuhan, Hubei, China.
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