1070-4272/01/7412-2017 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 12, 2001, pp. 2017!2020. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 12, 2001,
Original Russian Text Copyright + 2001 by Guzenko, Pakhlov, Lipkovskaya, Voronin.
AND ION-EXCHANGE PROCESSES
Sorption Modification of Fine Silica with Polyvinylpyrrolidone
N. V. Guzenko, E. M. Pakhlov, N. A. Lipkovskaya, and E. F. Voronin
Institute of Surface Chemistry, National Academy of Sciences of Ukraine, Kiev, Ukraine
Received July 19, 2000; in final form, December 2000
Abstract-The interaction of fine silica with polyvinylpyrrolidone in aqueous medium was studied by
Due to its specific properties, fine amorphous silica
is widely used in biotechnology, agriculture, medicine,
and pharmaceutics [1, 2]. Silica sorbents with required
properties can be prepared by their chemical modifica-
tion. Modification involves substitution of the initial
functional surface groups of silica by other groups
or coating of the surface by a monomolecular layer
of the corresponding polymer. Modification of the
surface of fine silica with polyvinylpyrrolidone (PVP)
allows preparation of silica sorbents with new prop-
Polyvinylpyrrolidone is used in medicine, phar-
macy, and cosmetics. This hydrophilic polymer is
soluble in water and other solvents and can participate
in complex formation. Such PVP properties as stabi-
lization of emulsions and suspensions, prolongation
of the effect of some drugs, and nontoxicity  are
important in the pharmaceutical industry.
In our study, we used A-300 brand Aerosil with
specific surface area of 287 m
, containing spher-
ical primary particles (9310 nm in diameter). The sur-
face of these particle contains isolated hydroxy groups
=Si3OH (silanol groups), hydroxy groups linked by
hydrogen bonds in various combinations, and molec-
ular water in various forms, from coordination-bound
to physically sorbed. The concentration of silanol
groups, which are the main sorption centers, on the
surface of the silica studied was 0.65 mmol g
the total water content, 435 wt %. Owing to hydro-
gen bonds, these primary Aerosil particles form sec-
ondary particles or aggregates 2003500 nm in diam-
eter [1, 4].
As modifying agent we used a 5% aqueous solu-
tion of pharmacopeia grade PVP (molecular weight
about 12000). Since PVP is rather hygroscopic, PVP
solutions are more convenient for experimental work
than powders. Aqueous PVP solutions are stable for
a long time after their sterilization for 15320 min.
In this work, we studied the interaction of fine sil-
ica with PVP and the effect of sorption modification
of the surface on some sorbent properties.
The PVP sorption was performed under static
conditions at room temperature. Solutions of PVP
(initial concentration 0.130.6 wt %) were mixed with
a 5% silica suspension so that the solution : sorbent
ratio was constant, 10 ml : 100 mg. After 1-h contact
the mixture was centrifuged for 30 min at 8000 rpm.
The amount of sorbed PVP was determined photocol-
orimetrically with iodine  from the difference in the
PVP concentrations in solution before and after inter-
action with silica.
The curve of PVP sorption on the fine silica sur-
face is described by the Langmuir isotherm (Fig. 1).
In the C
coordinates, where C
is the equilib-
Fig. 1. Isotherm of PVP sorption on the fine silica surface
(A) PVP sorption and (C
) equilibrium PVP concentration.