Adsorption Behavior of Perfluorinated Compounds on Thin-film Composite Membranes

Abstract

Perfluorinated compounds (PFCs), emerging contaminants, are globally distributed due to their persistent and bioaccumulative characteristics. The static adsorption behavior of PFCs on BW30, NF90, and NF270 membranes and the effect of the physico-chemical properties of the membranes and structure of Perfluorinated compounds (PFCs) on interactions between them have been thoroughly investigated. Two classes of PFCs were evaluated: perfluorosulfonic acid (PFOS) and perfluoroalkanoic acid with 5, 7, 9, and 11 carbon atoms. Adsorption of PFCs increased with increasing ionic strength, and decreasing pH due to decreased electrostatic repulsion between membrane surfaces and PFCs. The extent of PFOS adsorption on each membrane was higher than the extent of comparable perfluorononanoic acid (PFNA) adsorption. This is attributed to the easy migration of PFOS to the membrane surface from aqueous solution compared with PFNA. The adsorption of PFCs on thin-film composite membranes strongly depended on the material composing the active layer of the membranes. NF270 membranes (a piperazine based membrane) showed higher adsorption of PFOS and PFNA compounds compared with BW30 and NF90 membranes (polyamide based membranes). The BW30 polyamide membrane, which has a coating layer with aliphatic carbon and hydroxyl groups, had less interaction with PFOS and PFNA than the NF90 polyamide membrane. Increased chain length of PFCs increased adsorption.

This research shows that the adsorption behavior of PFCs on commercial thin-film composite membranes depends on the electrostatic interaction of both membranes and PFCs as a function of the applied solution chemistry, the active layer material of the membranes, and the chain length/functional group of PFCs