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

Abstract

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 the insufficient dissolution of the organic matter in fish scales; thus, the organic matter was difficult to completely dehydrate and condense, but formed nanosheet-like CDs, whose emission behavior had no significant correlation with excitation. Although the CDs prepared using the conventional hydrothermal had a lower doping amount of N element, the relative pyrrolic N content was higher, which was beneficial in improving their quantum yield. Additionally, the controllable high temperature and sealed environment used for the conventional hydrothermal could promote the dehydration and condensation of the organic matter in 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 exhibited higher quantum yield and excitation wavelength-dependent emission behavior.