Adsorption of phenolic compounds onto trimethylstearylammonium surfactant-immobilized cation-exchange membranes

Trimethylstearylammonium hydroxide/methoxide surfactants were immobilized onto two kinds of cation-exchange membranes (P81 and S2001) for the adsorption of phenolic compounds in the present study. The results indicate that the membrane with a doubled cation-exchange capacity (S2001) could attain nearly twice of the immobilized surfactant amount, but its surfactant immobilization % was close to or lower than the one with a smaller cation-exchange capacity (P81). By manipulating the feed surfactant concentration, different surfactant arrangements on the membrane surfaces (such as hemimicellar, admicellar, or mixed structure) could be produced. The membranes with theoretically 100% surfactant immobilization revealed the highest hydrophobicity level, and thus they were applied in the batch adsorption of phenolic compounds. According to the batch adsorption results of four phenolic compounds onto the surfactant-immobilized membranes (100% immobilization), the main adsorption mechanism should be hydrophobic interaction and the order of phenolic compound adsorptivity was phenol < 4-nitrophenol < 4-chloro-3-methylphenol ≤ bisphenol A, identical to their log Kow order. Moreover, in a batch adsorption/desorption cycle with 100 mL of 1 ppm bisphenol A aqueous sample tested and 5 mL of 2-propanol as the desorbent, the S2001 membrane (100% surfactant immobilization) could completely recover bisphenol A from water at a 20-fold enrichment.