Hydrodynamic Cavitation Fragmentizing Residue Carbon of Gasification Fine Slag into Carbon Dots

Using residual carbon of coal gasification slag as the start of a carbonaceous precursor, hydrodynamic cavitation has been successfully applied to prepare carbon dots (CDs) for the first time. When cavitation bubbles collapse, the comprehensive mechanical effects of shock wave, microjet, and high shear stresses fragment loose residual carbon into nanofragments or nanoparticles (namely CDs). The obtained CDs have a narrow size distribution, and most of them show an amorphous morphology due to disordered carbon accounting for the majority of CDs. The surface analysis reveals that the CDs have a few types but large numbers of surface groups. These structural characteristics of carbon core and surface groups result in two adjacent peaks appearing in the photoluminescence spectrum, and both peaks exhibit excitation-independent behaviors. A combination of core state and surface state is proposed to be responsible for the photoluminescence mechanism, which is also supported by the results of the photoluminescence time-resolved decay curve. Although the absolute quantum yield only is of 2.24% owing to simple core and surface groups without any functionalization, the CDs show good performances on Fe3+ detection and bioimaging, both of which are the commonest applications for CDs. Our research not only develops a new, facile, environmentally friendly, and cost-effective top-down strategy for CD preparation but also extends the knowledge into residual carbon as a CD precursor and explores an orientation for its high-value resource utilization.