Chitosan-Derived Carbon Dots with Room-Temperature Phosphorescence and Energy Storage Enhancement Properties

Carbon dots with fluorescence from blue to green have been prepared by a microwave-assisted hydrothermal reaction of a chitosan and sodium hydroxide solution. The carbon dots are conjugated graphite nuclei with developed groups on the surface. OH- acts as an activation agent to induce changes in carbon nuclei and surface properties, leading to a high percentage of C=O, CN=C, and C=C groups on carbon dots, which are crucial for n-pi* and pi-pi* transitions that contribute to emission at a long wavelength. Na+ is helpful in conquering quenching and favorable for the enhanced emission. When it is embedded into a matrix of PVA and boric acid, the composite exhibits obvious room-temperature property phenomena (RTP) that can be easily recognized by the naked eye for up to 12 s with a lifetime of up to 623 ms. The N and O atoms favor the facilitation of intersystem crossing (ISC) to effectively populate triplet excitons, which contributes to the RTP with a low energy gap. The carbon dots can also act as electron donors and enable a 184% capacitance increase in graphene oxide. The prepared carbon dots exhibit potential applications in the security, sensing, and energy storage fields.