Biomass-derived nitrogen self-doped carbon dots via a simple one-pot method: Physicochemical, structural, and luminescence properties

The efficient disposal and high-value utilization of biomass are crucial for easing the worsening environmental, resource, and energy situations. Green carbon dots (CDs) have got a lot of attention recently and biomass is a good green carbon source. In this work, cellulose and protein were used as typical components, and peanut shell, cotton stalk, and soymeal were utilized as typical biomass to synthesize nitrogen self-doped CDs with outstanding optical properties via a one-step and green microwave-assisted hydrothermal method without any additive. The reaction mechanism was briefly analyzed, and cellulose and protein differentiated the functional characteristics of the biomass-based CDs. A close connection was observed between optical properties and physicochemical structure, such as sp(2) C, N-doped surface states, and the synergy among them. Pyridinic N, amine N, and sp(2) C can reduce the bandgap. Quaternary N is beneficial for anti-interference in the CDs due to the large Stokes shift. The absolute photoluminescence quantum yields were measured as 2.83%-6.81%. The solid state of the CDs from protein, cotton stalk, and soymeal can emit clear cyan and claybank fluorescence under ultraviolet light. CDs prepared from cellulosic biomass and protein-rich biomass had significant differences in physicochemical, structural and luminescence characteristics.