Evaluation of the environmental impact and efficiency of N-doping strategies in the synthesis of carbon dots

Abstract

The efficiency and associated environmental impacts of different N-doping strategies of carbon dots (CDs) were evaluated. More specifically, N-doped CDs were prepared from citric acid via two main synthesis routes: Microwave-assisted hydrothermal treatment with addition of Ncontaining small organic molecules (urea and ethylenediamine (EDA); and microwave-assisted solvothermal treatment in N-containing organic solvents (n, n-dimethylformamide (DMF), acetonitrile and pyridine). These syntheses produced CDs with similar blue emission. However, XPS analysis revealed that CDs synthesized via both hydrothermal routes presented a better Ndoping efficiency (~15 at. %) than all three solvothermal-based strategies (0.6-7 at. %). However, from the former two hydrothermal strategies, only the one involving EDA as a nitrogen-source provided a non-negligible synthesis yield, which indicates that this should be the preferred strategy. This conclusion was supported by a subsequent life cycle assessment (LCA) study, which revealed that this strategy is clearly the most sustainable one from all five studied synthesis routes.