Chemical and morphological stability of Aliquat 336/PVC membranes in membrane extraction: A preliminary study

Aliquat 336/PVC-based polymer liquid membranes were used to extract Cd(II) and Cu(II) from aqueous solutions. The membranes demonstrated different extraction rate, capacity and chemical and morphological stabilities in the extraction of Cd(II) and Cu(II). Although the membrane showed good extraction rate and capacity to Cd(II), its chemical and morphological properties deteriorated badly after extraction. On the other hand, although the membrane showed a somewhat lower extraction capacity to Cu(II), it showed a much higher chemical and morphological stability. In this study, X-ray photoelectron microscopy (XPS) and lateral force atomic force microscopy (AFM) were used to characterize the chemical and morphological changes of the membrane before and after the extraction. The data in this work show that, XPS and AFM are good tools for membrane surface characterization. The sources of bleeding of the extractant (Aliquat 336) on membrane surface can be clearly identified. Although that actual cause of the membrane deterioration is not yet clear, the results from this work suggest that it could be related to the redistribution of the Aliquat 336 from the membrane bulk to the membrane surface. Information from this study is therefore useful to the future work on improving the membrane stability.