Mechanism investigation of synthesizing carbon quantum dots from coal by numerical simulation

Abstract

As fluorescent nanomaterial with excellent properties, carbon quantum dots have attracted significant attention. In particular, the synthesizing of carbon quantum dots has become the focus of various studies. Among them, carbon quantum dots synthesized from coal by strong acid oxidation have been widely studied for mass production. However, the broad size distribution of the products restricts their development, thereby prompting an issue that needs to be urgently resolved. Therefore, in this study, to achieve the control of size distribution, we simulated the diffusion process, in which sulfuric acid is inserted into the graphene layers of coal and destroys the van der Waals bonds. The result showed that when graphene layers are longer than 5 nm, the van der Waals bonds between them could not be broken within 10000 iterations. For bituminous carbon quantum dots, since its crystal structure size is small, the van der Waals bonds can be effectively broken, and narrow size distribution can be obtained at the 1500th iteration, which corresponds to the actual time of 34.2 h; for coke carbon quantum dots, since the crystal structure average size is larger than 5 nm, diffusion process cannot effectively break van der Waals bonds. The simulated result unravels the mechanism, guiding the experimental method to obtain a narrow size distribution and avoiding blind trials.