Sorption of Neutral Red Dye by Enterosorbent Polysorb MP from AOT Microemulsion in n-Decane

Neutral cationic red dye has been sorbed by Polysorb MP from a 0.25 mol/L AOT microemulsion in n-decane at different contents of the aqueous pseudophase. The maximum sorption capacity of the sorbent in the microemulsion is an order of magnitude higher than that in the water phase and amounts to 55 mg/g. A drastic drop in the degree of extraction upon increasing water content in the microemulsion from 1 to 8 vol % and the reversibility of the sorption processes have been revealed. Anionic dyes are not extracted by Polysorb in the same systems. As the water content increases, the zeta-potential of SiO2 particles decreases from 18 to 1 mV. On the basis of the obtained dependencies, a cation-exchange mechanism has been proposed for the sorption from the microemulsion, with this mechanism involving the exchange of sodium and neutral red dye cations between micelles adsorbed on the surface of particles and micelles contained in the bulk of the microemulsion.