A feasible and universal one-step method for functionalizing carbon dots efficiently via in-situ free radical polymerization

The passivation of carbon dots (CDs) are usually implemented through coupling reactions, which requires either specific functional groups on the surface of CDs or multiple steps. In this paper, we propose a feasible method to passivate CDs via in-situ free radical polymerization, which has no dependence on functional groups and thus is suitable for CDs prepared via either bottom-up or top-down route. Taking bare CDs that cut from active carbon by top-down method as an example. When putting acrylic acid, sodium methallyl sulfonate and acrylic phosphate ester as monomers into the bare CDs solution along with ammonium persulfate, stirring at room temperature for 2h, the monomers were polymerized and formed terpolymer-passivated CDs (T-CDs) of which quantum yields (QY) increased obviously. The QY of the bare CDs and the T-CDs were 0.2% and 29.1%, respectively. More interestingly, the bare CDs were found capable of constructing a redox-initiated couple with ammonium persulfate to initiate polymerization. Another example token to further approve the feasibility and universality of "in-situ free radical polymerization" passivation method is our reported poly (N-vinylcarbazole)passivated CDs (PVK-CDs) that prepared by bottom-up method. The PVK-CDs were synthesized via thermal treatment of a mixture composed of citric acid and N-vinylcarbazole molecules at 300 degrees C for 2 h. During the process the citric acid was carbonized to provide pristine CDs and N-vinylcarbazole was in-situ polymerized on the surface of the pristine CDs through thermal initiation, which enhances the fluorescence QY up to 40%.