Bimodal MWCNT-SiO2 mesoporous composites and related silicas with tubular morphology through an easy and fast protocol

Abstract

This work presents a straightforward preparative strategy for obtaining bimodal porous silica-based materials with tubular morphology (denoted as UVM-14). They include composites comprised of MWCNTs and a mesoporous silica coating, synthesized through a combination of hard and soft templating agents, specifically MWCNTs and surfactants. Two distinct materials may be obtained depending on the handling of this solid. The chemical extraction of the surfactant yields a core-shell composite that conserves the MWCNT core, coated with a mesoporous silica shell with pores arranged radially in relation to the nanotube axis. On the other hand, when the starting material is calcined, the two templating agents are eliminated. A silica with a hierarchical bimodal porosity is obtained, combining tubular cavities with a mesoporous shell. The synthesis methodology benefits from the optimal colloidal dispersion of non-covalently functionalized MWCNTs with CTAB prepared using a mechanochemical process. Also, the atrane method (using silatrane as Si source and working in a hydroalcoholic medium) is crucial to obtain a complete, very homogeneous, and modulable (in thickness) nanotube coating with a mesostructured silica shell. Typically, surface areas round 1100 m² g⁻¹ and pore diameters of 2.5 and 15–35 nm can be prepared. The structure of the materials can be adjusted by modifying the length of the nanotubes and the thickness of the porous silica layer.