Electron-beam radiation-induced ultrafast synthesis of highly conjugated carbon quantum dots with excellent fluorescence intensity

A steadily increasing research interest has been devoted to carbon quantum dots (CQDs) as a highly promising visible-light-triggered material. However, the commonly used hydrothermal reaction method to produce CQDs is usually a lengthy and tedious process, which requires elevated temperatures. Herein, we report for the first time the rapid synthesis of highly conjugated CQDs using lignin as the precursor activated by high-energy electron-beam radiation from an electron accelerator at different doses (0–400 kGy). Lignin was used as the raw material for the generation of lignin fractions with different molecular weights by employing electron-beam radiation under ambient conditions within minutes, and the CQDs were directly obtained via centrifugation and dialysis. The CQDs obtained at an irradiation dose of 250 kGy have the highest fluorescence intensity. At a radiation dose of 250 kGy, the electron beam depolymerizes lignin into numerous small molecule fragments; these low-molecular-weight units can form a large number of highly conjugated carbon core structures (C=C), leading to a remarkable enhancement of the fluorescence intensity of CQDs. The synthesized CQDs have a positive effect on tomato photosynthesis at a concentration as low as 250 mg/L. This study establishes a new strategy for the large-scale synthesis of CQDs with higher fluorescence intensities, and the findings provide valuable ideas for future studies of electron-beam radiation-assisted synthesis of CQDs.