CO2-Switchable Reversible Phase Transfer of Carbon Dots

Carbon dots (CDs) have attracted great attention in recent years owing to their potential applications in such as photocatalysts, organic synthesis, and bioimaging. However, it is always difficult for the separation and recycling of carbon dots from homogeneous reaction systems, which may limit their application in catalysis. A stimuli-responsive phase transfer of CDs is promising to solve these problems. In this work, we developed a novel class of CO2-responsive carbon dots decorated with different molecular weight polyetheramines (PEAs) (Mn = 230, 400, 2000 g/mol, respectively) and investigated their phase transfer behavior. It was found that PEA230-CD were well able to reversibly transfer between water and organic solvents by alternative bubbling and removal of CO2, the phase transfer efficiency of PEA400-CD was about 40%, and PEA2000-CD cannot transfer. The mechanism of the CO2-switched phase transfer involves the reversible reaction of PEA-functionalized CDs with CO2 and reversible formation of hydrophilic bicarbonates salts. As an example of applications, the phase transfer strategy was successfully applied in a Henry reaction by using the CDs as catalysts for efficient homogeneous catalysis, heterogeneous separation, and recycling of the CDs.