Tunable Multicolor Luminescent Carbon Dots from Birch Leaves via a Sequential Segregation Approach

Leaves have recently emerged as a popular sustainable and abundant source for the synthesis of optically active carbon dots (CDs), in part because their rich chemical composition could enable for the formation of a wide variety of CD properties. However, this chemical complexity also poses a significant challenge for the control of the properties of CDs, and the fact is that the synthesis of leaf-derived CDs with desired properties commonly requires a highly labor-intensive trial-and-error process. In this study the issue is addressed through a straightforward sequential extract segregation method. The desired constituents from birch leaves are first selectively isolated based on their solubility and thereafter projected into hydrothermal and solvothermal reactions, where three different types of CDs with distinct emission colors: blue (λpeak = 446 nm), green (λpeak = 530 nm), and red (λpeak = 675 nm) are produced. This study thus highlights the importance of pre-extraction and constituent isolation of complex biomass for the direction of the CD synthesis towards tailored properties. The application potential of the synthesized CDs as effective and safe antioxidants has been finally evaluated.