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, C–N═C, and C═C groups on carbon dots, which are crucial for n−π* and π–π* 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.