From Helixes to Mesostructures: Evolution of Mesoporous Silica Shells on Single-Walled Carbon Nanotubes

Constructing a novel nanoplatform by integrating single-walled carbon nanotubes (SWCNTs) and mesoporous silica is of considerable interest due to their combined advantages. However, it is difficult to coat SWCNTs with mesoporous silica shells (MSS). Conventional mechanisms used in the formation of mesostructured materials can not be simply applied in this coating process because the diameter of SWCNTs is smaller than the size of surfactant micelles. Here we report the formation mechanism of MSS on SWCNTs (SWCNTs@MSS), which involves the structural evolution from helixes to mesostructures for the first time. The evolution process mainly includes four stages. The first stage is the transition from tight surfactant helix to loose silica-surfactant composite helix, followed by a second stage of gap filling process on the silica-uncovered surfaces. Afterward, the surfactant/silicate composite micelles further self-assemble onto nanotubes with the increase of diameter in the third stage. Finally, the silicate frameworks further condense to obtain stable mesostructures. The obtained SWCNTs@MSS with outstanding features exhibit high potential for cancer treatment and also promise future applications in other various fields.