Rapid, Solvent-Free Synthesis of Amorphous, Photoluminescent, Carbon Nanodots from Imidazole and Maleic Anhydride Solids

A facile, rapid, and sustainable synthesis of amorphous, photoluminescent, carbon nanodots in high yields (∼51%), by cogrinding of maleic anhydride and imidazole, is reported for the first time. The heat liberated during the exothermic oligomerization of maleic anhydride, initiated by imidazole in the solid state, was identified to be the cause of carbonization of the reaction mixture. These carbon nanodots showed very low cytotoxicity toward mesenchymal stem cells, even at very high concentrations (1 mg/mL). Having the highest adsorption capacity for ammonia among unmodified carbons reported to date (∼19.3 mg/g), these carbon nanodots could be used for the removal of ammonia from the gas phase. In addition, these carbon nanodots could be used as an ionotropic cross-linker for chitosan, to prepare stable gels, suitable for a wide variety of applications. In contrast to the present solid-state methodologies which involve the use of hazardous chemicals or high temperatures, this solvent-free method of preparing carbon nanodots is sustainable, facile, safe, and inexpensive.