Scalable production, cell toxicity assessment, and plant growth promotion activities of carbon quantum dots derived from low-quality coal feedstock

Carbon quantum dots (CQDs) have several novel opto-chemical characteristics and potential uses in biomedicine, imaging, catalysis, and sensing. However, there are cost and technical limitations with scaling up the synthesis of CQDs for fulfilling its current demand. We propose a simplistic, innovative, sustainable, and economically scalable method for the formation of fluorescent nitrogen and sulphur co-doped CQDs (NS-CQDs) by utilizing bulk, low-grade subbituminous coal as feedstock. The co-doped NS-CQDs were identified using a suite of microscopic and spectroscopic approaches. We suggest that heteroatoms (i.e., N and S) are effectively self-doped on CQDs surfaces/edges of the carbon nanostructure either by functionalization or by getting incorporated on the edges during the oxidative process. The coal-derived CQDs show blue and cyan fluorescence with quantum yields of 9.35 and 16.96%, respectively. The cytotoxicity, genotoxicity, and reactive oxygen species (ROS) of the coal-derived CQDs were evaluated using a rodent hepatocyte cell line, which revealed that these CQDs are biocompatible, non-cytotoxic, and non-genotoxic. Moreover, these coal-derived CQDs also have proved to be good carriers of nutrients and microbes for plant growth promotion, effectively behaving as a nanofertilizer. Their phytotoxicity and impact on plant metabolites and antioxidant properties of the carbon quantum dot products have also been examined in our study.