Hydrolysis sol-gel way

More specifically, tetrafluoroborate anion showed an outstanding catalytic activity in hydrolysis [23]. [BF4] anion is known to undergo some hydrolysis in the presence of water, even at room temperature, and releases some HF, which is known as a very powerful catalyst for hydrolytic condensation of alkoxysilanes. 

Note that the in situ formation of HF using BF4 anions led to some fluorination of the sihca surface based on F MAS NMR [18]. 

Besides, the intrinsic catalytic activity of the anion, physical properties associated with the choice of anion, such as viscosity and water miscibihty, most probably influence the whole sol-gel process. The nature of the anion determines the formation of more or less compact (more or less organized) ion aggregates and the interactions with the growing silica interface, which finally may result in structure directing and/or protecting layers on the pore walls [24]. 

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