Luminescent carbon dots obtained from chitosan: a comparison between different methods to enhance the quantum yield

The preparation of carbon dots (CDs) from different biomass source represents an interesting alternative to obtain these nanoparticles, mainly when they can be prepared using low-cost methods. In this work we have used a nitrogen-rich precursor, chitosan, to obtain CDs using two different methods, acid dehydration (AD) and hydrothermal carbonization (HC), with the aim to study the different characteristics of the obtained nanoparticles. Also, a simple method to functionalize the CDs was applied to enhance the optical properties of the carbon nanoparticles. The obtained CDs were characterized by several techniques including FTIR, Elemental Analysis, TEM, UV-Vis, Fluorescence, and Potentiometric Titration. Size distribution measurements showed that the CDs had a narrow size distribution, with the diameters in the range 1.0-3.6 nm. Also, the CDs obtained by the HC method showed a greater amount of nitrogen functional groups than the nanoparticles prepared by the AD route. The functionalized CDs obtained from the HC method reached 15.3% of quantum yield. Furthermore, the obtained CDs were used as fluorescent sensors for different metal ions. Finally, these results represent an alternative to obtain biomass-derived CDs prepared via a low-cost method, presenting a relatively high quantum yield with potential applications in different areas.