Tailoring the structure and hydrophobic properties of amorphous silica by silylation

The structure and hydrophobic nature of sot-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. (C) 2012 Elsevier Inc. All rights reserved.