Nitrogen-rich soybean protein isolate derived “Self-Doping” carbon nano-onions for luminescence properties

Carbon nano-onions (CNOs) were successfully obtained for the first time through a simple one-pot Microwave hydrothermal carbonization (MHTC) method at low temperature by using biomass macromolecules as the raw materials. The effects of different reaction temperatures and residence times on the characteristics and yield of CNOs were studied. High-resolution transmission electron microscopy (HRTEM) images reveal CNOs with a regular concentric carbon shell structure with 10–20 layers, obvious crystal characteristics, and the lattice spacing of 0.34 nm. X-ray photoelectron spectroscopy and photoluminescence spectroscopy were applied to reveal the effects of different nitrogen forms and hybrid structures of carbon on the fluorescence properties of CNOs. Results showed that reaction temperature affected the structure of CNOs mainly by regulating the degree of carbonization, and residence time mainly affected the aromatization of CNOs. In addition, nitrogen self-doping CNOs prepared at low temperature also have good fluorescence performance. Most strikingly, the stable blue light emission by nitrogen self-doping CNOs could be the combination of the fluorescence of the carbon shell sp² structure and that of surface functional groups. Taking advantage of the above unique fluorescent behavior, CNOs are prepared as fluorescent anticounterfeiting printing to achieve data encryption and decryption.