PDF(Pubmed)
Abstract：
In-depth insights into the oligomers of carbon dots (CDs) prepared from small-molecule precursors are important in the study of the carbonization mechanism of CDs and for our knowledge of their complex structure. Herein, citric acid (CA) and ethylenediamine (EDA) were used as small-molecule precursors to prepare CDs in an aqueous solution. The structure of oligomers acquired from CA and EDA in different molar ratios and their formation process were first studied using density functional theory, including the dispersion correction (DFT-D3) method. The results showed that the energy barrier of dimer cyclization was higher than that of its linear polymerization, but the free energy of the cyclized product was much lower than that of its reactant, and IPCA (5-oxo-1,-2,3,5-tetrahydroimidazo [1,2-a]pyridine-7-carboxylic acid) could therefore be obtained under certain conditions. The oligomers obtained from different molar ratios of EDA and CA were molecular clusters formed by short polyamide chains through intermolecular forces; with the exception of when the molar ratio of EDA to CA was 0.5, excessive CA did not undergo an amidation reaction but rather attained molecular clusters directly through intermolecular forces. These oligomers exhibited significant differences in their surface functional groups, which would affect the carbonization process and the surface structure of CDs.
摘要：
对由小分子前体制备的碳点（CD）低聚物的深入了解对于研究CD的碳化机理以及我们对其复杂结构的了解非常重要。在这里，使用柠檬酸（CA）和乙二胺（EDA）作为小分子前体在水溶液中制备CD。首先使用密度泛函理论研究了从不同摩尔比的CA和EDA获得的低聚物的结构及其形成过程，包括色散校正(DFT-D3)方法。结果表明，二聚体环化的能障高于其线性聚合的能障，但是环化产物的自由能远低于其反应物的自由能，因此，在某些条件下可以获得IPCA（5-氧代-1，-2,3,5-四氢咪唑并[1,2-a]吡啶-7-羧酸）。从不同摩尔比的EDA和CA获得的低聚物是由短聚酰胺链通过分子间力形成的分子簇;除了当EDA与CA的摩尔比为0.5时,过量的CA不经历酰胺化反应,而是直接通过分子间力获得分子簇。这些低聚物在其表面官能团方面表现出显著差异,这将影响CD的碳化过程和表面结构。
