Revealing the Dynamic Formation Process and Mechanism of Hollow Carbon Spheres: From Bowl to Sphere

Hollow carbon spheres are attracting great attention due to their great potential uses in drug delivery, energy storage, and catalysis. However, the formation process and mechanism of the hollow carbon spheres are still unclear. Herein, we chose glucose as a carbon precursor and double surfactants poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) triblock copolymers and sodium oleate as the soft template. The synthesis process of hollow carbon spheres was investigated in the coupling of a soft templating method and hydrothermal carbonization system by regulating the reaction time. A dynamic formation process of the hollow carbon spheres was identified based on the results from scanning electron microscopy and transmission electron microscopy images, in which three evolution stages were seen including hollow carbon bowls, capsules, and spheres. In addition, the formation mechanism was also presumed: During the synthesis process, the double surfactants interacted with each other to act as the soft template, and the glucose underwent hydration, polymerization, and aromatization stages. When the concentration of aromatic compounds reached the critical supersaturation, the nucleation took place from a point and extended outward gradually along the interface to widen and thicken the carbon shell, resulting in different hollow structured carbon particles being formed successively by controlling the reaction time. Furthermore, the resultant hollow structured carbon particles were stable and uniform, and we made preliminary explorations on their biochemical and electrochemical performance.