How are Silanol groups functionalized unto mesoporous silica structures?

As described in this research paper:


Immobilization of Jacobsen type catalysts on modified silica, Jairo Cubillos , Edwing Grajales, Santiago Vásquez, Consuelo Montes de Correa, Rev. Fac. Ing. Univ. Antioquia N.° 57 pp. 38-48. Enero, **2011** ([link](http://www.scielo.org.co/scielo.php?script=sci_arttext&pid=S0120-62302011000100005&lang=en))


The Jacobsen type catalysts are attached unto the silica through a reaction between Silanol that is already part of the silica and 3-APTES. However, there is no mention on how these Silanol molecules were already present in the silica. Any idea?




The bulk of silica is indeed silicon dioxide, but at surface there is a discontinuity. The dangling O, exist as OHs, as silanols. Therefore silica *surface* itself is full of silanols, which are used for functionalizing silica. Native silica looks like the following with various *types* of silanols. APTES is a very common chemistry in the silica modification chemistry.


Note silicon dioxide, like quartz may not be easily to functionalized because the surface area is very low and therefore the number of silanols is also low.


[![enter image description here](https://i.stack.imgur.com/7biTv.png)](https://i.stack.imgur.com/7biTv.png)


Ref:High-Performance Precoated Stationary Phases, Colin F. Poole, in Instrumental Thin-Layer Chromatography, 2015


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