Sustainable strategies are increasingly required to enhance the optoelectronic performance of biopolymers while ensuring environmental safety. In this work, carbon quantum dots (CQDs) were synthesized via a green hydrothermal route using Morus alba waste biomass leaves. The CQDs exhibited abundant oxygen- and nitrogen-containing functional groups, enabling strong interfacial interaction with the chitosan (CS) matrix and leading to significant modification of its optical properties. The composite system was designed primarily for optoelectronic and UV–optical applications, particularly for bandgap tuning and light–matter interaction control. The CQDs showed strong blue photoluminescence with a quantum yield of 9.46%, and characteristic π–π* and n–π* transitions at 251 nm and 356 nm. Structural analysis confirmed disruption of the semicrystalline CS matrix and strong CQD–polymer interaction. UV–Vis results revealed a substantial reduction in the optical bandgap from 4.97 eV (pure CS) to 2.35 eV (CS/CQDs-20), along with increased Urbach energy, indicating enhanced disorder and localized states. Further optical analysis showed improved refractive index, dielectric constant, and optical conductivity, accompanied by increased carrier concentration and reduced optical resistivity (from 0.0519 to 0.0033 Ω·m). These results demonstrate that CQD incorporation effectively tailors the optical and electronic behavior of chitosan, making the composites suitable for optoelectronic devices, UV-active coatings, and light-responsive polymer systems.
Mamand et al. (Sat,) studied this question.