A universal strategy to separate hydrophilic hybrid-light carbon quantum dots using pure water as eluent

A sustainable separation technique is a key to obtaining high-purity monochrome fluorescent carbon quantum dots (CQDs), which have broad potential applications in light-emitting diodes, bioimaging, and biomedicine. In this work, a green, tenable, and universal method of effectively separating a large number of hydrophilic hybrid-light CQDs using pure water as the eluent was demonstrated for the first time. Just after one separation, multicolor fluorescent CQDs can be divided into two, three, and four CQDs with a gradient of fluorescent colors ranging from blue to orange under UV light irradiation, in accordance with the increasing size of CQDs. The larger red-shift of the fluorescent color of CQDs before separation, the more the quantity of fluorescent CQDs were obtained after separation. Comparing with multicolor CQDs, the separated CQDs reveal similar structure characteristics, higher color-purity, narrower full width at half maximum, and better excitation-independent performance. This separation strategy relies on the adsorption capacity-size effect. Our finding opens the door to make separating hydrophilic hybrid-light CQDs practical and straightforward, which will expand the potential applications of hydrophilic CQDs.