Question

The surface chemistry of silica ,I want some information about that ?

Answer 1

The surface chemistry of silica:

The ultimate particles, which make up the silicas, are polymers of silicic acid, consisting of interlinked SiO₄tetrahedra. At the surface, the structure terminates in either a siloxane group (≡Si-O-Si≡) with the oxygen on the surface, or one of several forms of silanol groups (≡-Si-OH). The silanols can be divided into (1) isolated groups (or free silanols), where the surface silicon atom has three bonds into the bulk structure and the fourth bond attached to a single OH group and (2) vicinal silanols (or bridged silanols), where two single silanol groups, attached to different silicon atoms, are close enough to hydrogen bond. A third type of silanols—geminal silanols—consists of two hydroxyl groups attached to one silicon atom. The geminal silanols are too close to hydrogen bond each other, whereas the free hydroxyl groups are too far separated. The surface structure of amorphous silica is highly disordered, so a regular arrangement of hydroxyl groups cannot be expected. Hence, the surface of amorphous silica gel may be covered by isolated and vicinal hydroxyl groups. Irrespective of whether a surface contains both types or only isolated hydroxyl groups (as in crystalline silica), complete surface coverage can be achieved: the surface is fully hydroxylated.