Scalable synthesis of highly photoluminescence carbon quantum dots
Graphical abstract
Introduction
CQDs including graphene quantum dots, carbon nanodots and carbon polymer dots [1] have been extensively studied since the first report in 2004 by Xu et al [2]. Due to their visible photoluminescence, biocompatibility and ease of surface functionalization [3], [4] CQDs have emerged as potentials materials for biomedical applications [5], [6]. Although CQDs could be synthesized by numerous methods using a wide range of carbon resources hydrothermal treatment of CA and EDA are preferred to prepare water-soluble and highly photoluminescence CQDs [3], [7], [8] (SI, Table S1). Unfortunately, hydrothermal synthesis is difficult to scale up by increasing either reaction volume or substances concentration because the temperature and concentration profiles that are key factor for the nucleation and growth of nanocrystals will significantly change [9], [10]. This letter reports the use of Gly as a high-boiling point solvent that allows scaling up the synthesis of CQDs.
Section snippets
The synthesis and purification of CQDs
Chemicals including CA, EDA and Gly were purchased from Aladdin chemicals. A mixture solution of CA (5 M) and EDA in Gly with a molar ratio CA/ED of 0.5 was placed in a microwave oven (Sunhouse, SHD4823) operating 750 W for 7 min continuously. After the reaction, CQDs were precipitated by adding mixture of acetone and ethanol (8:2 by volume) and collected by centrifugation. CQDs were dispersed in water, re-precipitated with acetone and collected by the centrifugation at 5 °C (10000 rpm,
Results and discussion
The formation of CQDs from CA and EDA under hydrothermal conditions has been discussed previously [11], [12]. Briefly, intramolecular dehydration condensation forms intermediate fluorophores such as imidazo[1,2-a]pyridine-7-carboxylic acid, 1,2,3,5-tetrahydro-5-oxo- (IPCA) [11]. IPCA involves in carbonization processes resulting in CQDs containing IPCA on the surfaces [13], [14]. In current study, the dehydration and carbonization processes were enabled by heating CA and EDA in Gly under
Conclusion
The scalable synthesis of CQDs has been demonstrated; over 10 g of CQDs could be obtained by heating CA and EDA in Gly. CQDs were spherical, contained C sp2 domains in the core and IPCA on the surfaces. The optical properties of CQDs were largely dominated by the surface IPCA that was an intermediate product formed at about 160 °C and retained on the CQDs surfaces after carbonization processes. The method demonstrated here in would pave a new way to deploy CQDs in diverse applications.
CRediT authorship contribution statement
Xuan-Dung Ma:Funding acquisition, Conceptualization, Supervision, Writing - review & editing, Software. Tran Thi Kim Chi: Formal analysis, Validation, Visualization, Methodology, Writing - original draft. Truong-Chung Nguyen: Investigation, Writing - original draft. Van-Thao Ta: Formal analysis, Data curation, Writing - original draft.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgment
This research was funded by Vietnam Ministry of Education & Training, Hanoi Pedagogical University 2, and Chemedic Company under grant number B.2018-SP2-13 Vietnam Ministry of Education & Training, Vietnam; Hanoi Pedagogical University 2, Vietnam and Chemedic Company, Vietnam under grant number B.2018-SP2-13.
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