Methyltrimethoxysilane silica aerogel composite with carboxyl-functionalised multi-wall carbon nanotubes

To complement the low mechanical strength of pristine methyltrimethoxysilane (MTMS) silica aerogels, a composite silica aerogel with structurally strong multi-wall carbon nanotubes (MWCNTs) was synthesised by supercritical drying. The surface structure of stable MWCNTs was oxidised and defected by acid treatment to attach carboxyl groups, which result in good dispersibility of the MWCNTs. By a sol–gel process, functionalised MWCNTs formed a network structure with the MTMS silica sol. Through the compositisation of the MTMS silica aerogel with functionalised MWCNTs, the mechanical strength of the composite aerogel became higher than that of the pristine MTMS silica aerogel; changes in the surface characteristics, chemical bonding state, and microstructure were also observed. The aerogels exhibit hydrophobicity except at the functionalised MWCNTs, which impart hydrophilicity due to polar functional groups. Chemical bonding, including carbonyl and carboxyl bonds, was also observed following functionalisation. Some fibre structures of MWCNTs and pore characteristics in composites were observed.