Hollow Carbon Nanobubbles: Synthesis,Chemical Functionalization,and Container‐Type Behavior in Water

Thin‐walled, hollow carbon nanospheres with a hydrophobic interior and good water dispersability can be synthesized in two steps: First, metal nanoparticles, coated with a few layers of graphene‐like carbon, are selectively modified on the outside with a covalently attached hydrophilic polymer. Second, the metal core is removed at elevated temperature treatment with acid, leaving a well‐defined carbon‐based hydrophobic cavity. Loading experiments with the dye rhodamine B and doxorubicin confirmed the filling and release of a cargo and adjustment of a dynamic equilibrium (cargo‐loaded versus release). Rhodamine B preferably accumulates in the interior of the bubbles. Filled nanobubbles allowed constant dye release into pure water. Studies of the concentration‐dependent loading and release show an unusual hysteresis.