The chemical composition of the medical enterosorbent Polisorb MP (colloidal silica particles) and its surrounding dispersive medium was determined using AES ICP, CHNS analysis, TGA, and capillary electrophoresis. Dispersions of Polisorb in water and in 40% and 95% aqueous-ethanol solutions were prepared and characterized by photon correlation spectroscopy (PCS) and phase analysis light scattering (PALS). The number-average hydrodynamic diameter of fractal-like aggregates of primary particles was 105 – 135 nm, and the electrophoretic potential ranged from –28 to –22 mV. The charge of a single aggregate decreased with increasing alcohol content in the sequence: –89, –54, and –29 e. The maximum sorption of methylene blue sharply decreased from 10 to 0.7 mg/g under these conditions. It was shown that the maximum sorption values significantly exceed the number of negative surface centers calculated by PALS within the spherical aggregate model, but are lower than the number of silanol groups determined by TGA. A cation-exchange mechanism for the sorption of cationic dyes by Polisorb MP is hypothesized.
T.Yu. Podlipskaya (Wed,) studied this question.