Mechanistic Insight into the Synthesis and Morphological Evolution of Superhydrophobic Silica Nanotubes

Silica nanotubes have significant applications in various fields, including thermal insulation, self-cleaning, and catalysis. Currently, the synthesis methods of silica nanotubes are mostly limited to the template method. In this work, a template-free strategy and vapor-phase approach were used to prepare silica nanotubes. Poly(methylhydrosiloxane) (PMHS) was hydrolyzed and condensed in a high-temperature closed reactor by using ammonia as a catalyst. The resulting product was then subjected to template-free self-assembly to synthesize silica nanotubes incorporating methyl groups. The silica nanotubes were synthesized under varying conditions, resulting in lengths ranging from 50 nm to several micrometers, exterior diameters between 40 and 120 nm, and wall thicknesses varying from 7 to 30 nm. The synthesized products underwent morphology analysis using TEM and FESEM for morphology analysis, elemental composition analysis using XPS, and chemical structure identification using FTIR, and the possible formation mechanism of silica nanotubes formation was also speculated. Furthermore, the coatings formed by silica nanotubes exhibited remarkable superhydrophobic self-cleaning properties with a water contact angle of 162° and a rolling angle of less than 1°.