Luminescent Carbon Dots from Wet Olive Pomace: Structural Insights, Photophysical Properties and Cytotoxicity

Carbon dots as new antioxidants: Synthesis, activity, mechanism and application in the food industry

Antioxidants not only prevent food spoilage, but also maintain the nutritional value of food, thereby exerting a crucial protective effect on food industry. Nanomaterials have recently been used as antioxidants because of their remarkable potential to scavenge free radicals. Of them, owing to their relatively high biocompatibility and unique physicochemical properties, carbon dots (CDs) have garnered considerable attention. This paper reviews research progress on CDs as new antioxidants. We here first discuss the methods for synthesizing various antioxidant CDs, followed by the antioxidant activities of different CDs and factors influencing these activities. Then, the possible action mechanisms of antioxidant CDs are discussed. The review particularly focuses on the application of antioxidant CDs, especially in the food industry, including antioxidant coatings, antioxidant packaging materials, and nano-level food additives. Finally, the challenges and prospects for CDs as new antioxidant are described.

Are "Carbon Dots" Always Carbon Dots? Evidence for their Supramolecular Nature from Structural and Dynamic Studies in Solution and in the Pure Solid

A model for the morphology (size, shape, and crystallinity) of carbon dots (CDs) in the solid state consistent with the observed photoluminescence in solution is proposed herein. Overwhelming evidence has been collected that links the data coming from solid-state analysis (high-resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS)) to that of solution (pulsed-field gradient (PFG)-NMR spectroscopy, time-resolved fluorescence anisotropy (TRFA), and steady-state/time-resolved fluorescence), allowing the establishment of an overall structural model for CDs. According to this model, the so-called carbon dots, observed under HRTEM imaging, are in fact supramolecular organized structures dynamically assembled from small to medium-sized molecular species when the solvent is removed to give the solid form. In this way, the imaged nanoparticles (TEM/AFM) are not covalently bound entities formed during the synthetic process, but instead supramolecular entities formed by noncovalent interactions. These particles, if at all present in solution, have the form of loose associations of relatively small molecules. This study was conducted on CDs obtained from the hydrothermal carbonization (HTC) of a biomass waste (olive wet pomace).

Insight into the differences in carbon dots prepared from fish scales using conventional hydrothermal and microwave methods

The preparation of carbon dots (CDs) from waste fish scales is an attractive and high-value transformation. In this study, fish scales were used as a precursor to prepare CDs, and the effects of hydrothermal and microwave methods on their fluorescence properties and structures were evaluated. The microwave method was more conducive to the self-doping of nitrogen due to rapid and uniform heating. However, the low temperature associated with the microwave method resulted in insufficient dissolution of the organic matter in the fish scales, resulting in incomplete dehydration and condensation and the formation of nanosheet-like CDs, whose emission behavior had no significant correlation with excitation. Although the CDs prepared using the conventional hydrothermal method showed lower nitrogen doping, the relative pyrrolic nitrogen content was higher, which was beneficial in improving their quantum yield. Additionally, the controllable high temperature and sealed environment used in the conventional hydrothermal method promoted dehydration and condensation of the organic matter in the fish scales to form CDs with a higher degree of carbonization, uniform size, and higher C = O/COOH content. CDs prepared using the conventional hydrothermal method exhibited higher quantum yields and excitation wavelength-dependent emission behavior.