Green preparation of GQDs with small particle size, low defects, and high quantum yield by using hydrodynamic cavitation technology

In this work, the hydrodynamic cavitation (HC) method with simple operation, low cost, high safety and largescale production was applied to prepare GQDs. The expandable graphite powder as the raw material was treated by utilizing a microwave oven and then continuously exfoliated in venturi HC device. Finally, the GQDs with the advantages of small particle size, uniform size distribution, low defects, good water solubility and high quantum yield can be obtained by simple filtration. The GQDs are prepared by using the HC method without the use of acids and the introduction of impurities in the entire preparation process. The effects of HC cycle time, inlet pressure and fluid temperature on the property of GQDs were investigated. The results showed that GQDs with particle size of 1.77 +/- 0.03 nm, size distribution in the range of 1.25-2.25 nm and fluorescence quantum yield of 36.77 % were obtained at 14 h HC cycling time, 3.0 bar inlet pressure and 50 degrees C temperature. The obtained GQDs solution has the advantages of strong fluorescence, high concentration and good stability. According to the atomic force microscope (AFM) image analysis, it can be seen that the HC technique can be used to prepare single-layer GQDs. It is hoped that the present work can provide a possibility for the preparation of few-layer GQDs on a certain scale.