Tailoring the structure and hydrophobic properties of amorphous silica by silylation

The structure and hydrophobic nature of sol–gel mesoporous silica were modified by silylation using trimethylchlorosilane. The efficiency of the process can be enhanced by fine tuning a key sol–gel parameter, the water/precursor molar ratio, thus reducing the amount of silylating agent needed to achieve almost full surface derivatization. It is shown that the modifications imposed by silylation are extensive: the inclusion of the bulky hydrophobic silyl groups does not merely change the chemical nature of the pore walls surface, but induces a deep structural rearrangement of the silica backbone itself, since the pores change in shape and orientation, and the molecular structure has to accommodate the tensions induced by such reorientation. It is possible to tailor simultaneously the hydrophobic properties and the pore morphology of the modified silica by a combined choice of the hydrolysis and silylation ratios.

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► Silylation with TMCS modified the structure and hydrophobicity of sol–gel silica.
► The water/precursor molar ratio (R) is a key parameter in the silylation efficiency.
► By fine tuning R, the amount of TMCS to achieve full derivatization is reduced.
► It is possible to tailor at once the hydrophobic properties and the pore morphology.