A review article is presented of the research results obtained by the autho
r on the properties of amorphous silica surface. It has been shown that in
any description of the surface silica the hydroxylation of the surface is o
f critical importance. An analysis was made of the processes of dehydration
(the removal of physically adsorbed water), dehydroxylation (the removal o
f silanol groups from the silica surface), and rehydroxylation (the restora
tion of the hydroxyl covering). For each of these processes a probable mech
anism is suggested. The results of experimental and theoretical studies per
mitted to construct the original model (Zhuravlev model-1 and model-2) for
describing the surface chemistry of amorphous silica. The main advantage of
this physico-chemical model lies in the possibility to determine the conce
ntration and the distribution of different types of silanol and siloxane gr
oups and to characterize the energetic heterogeneity of the silica surface
as a function of the pretreatment temperature of SiO2 samples. The model ma
kes it possible to determine the kind of the chemisorption of water (rapid,
weakly activated or slow, strongly activated) under the restoration of the
hydroxyl covering and also to assess of OH groups inside the SiO2 skeleton
. The magnitude of the silanol number, that is, the number of OH groups per
unit surface area, alpha(OH), when the surface is hydroxylated to the maxi
mum degree, is considered to be a physico-chemical constant. This constant
has a numerical value: alpha(OH,AVER) = 4.6 (least-squares method) and alph
a(OH,AVER) = 4.9 OH nm(-2) (arithmetical mean) and is known in literature a
s the Kiselev-Zhuravlev constant. It has been established that adsorption a
nd other surface properties per unit surface area of silica are identical (
except for very fine pores). On the basis of data published in the literatu
re, this model has been found to be useful in solving various applied and t
heoretical problems in the field of adsorption, catalysis, chromatography,
chemical modification, etc. It has been shown that the Brunauer-Emmett-Tell
er (BET) method is the correct method and gives the opportunity to measure
the real physical magnitude of the specific surface area, S-Kr (by using lo
w temperature adsorption of krypton), for silicas and other oxide dispersed
solids. (C) 2000 Elsevier Science B.V. All rights reserved.