Multifaceted role of H2O2 in the solvothermal synthesis of green-emitting nitrogen-doped graphene quantum dots†

Abstract

Fluorescent nitrogen-doped carbon dots (N-GQDs) with long-wavelength emission properties are of increased interest for technological applications. They are widely synthesized through the solvothermal treatment of graphene oxide (GO) using N,N-dimethylformamide (DMF) as a cleaving and doping agent. However, this process simultaneously generates undesired interfering blue-emissive by-products. In this study, we present a straightforward method for synthesizing N-GQDs exclusively exhibiting green fluorescence. The key innovation lies in the addition of hydrogen peroxide (H₂O₂) to the DMF-driven one-pot solvothermal cleavage process. Systematically controlling the reaction conditions, we elucidate the threefold beneficial role of H₂O₂: first, it acts as a radical source facilitating the degradation of DMF and the generation of nitrogen-containing radicals, essential for N-GQD formation; second, it prevents the thermal reduction of GO, thus ensuring persistent reaction pathways with DMF-derived radicals; and third, it suppresses the self-reaction of DMF-derived radicals, thereby avoiding the formation of undesired blue-fluorescent by-products. Our findings on the reaction mechanism and the advantageous role of H₂O₂ open new possibilities for the rational design of N-GQDs genuinely emitting at long wavelengths.