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Transport of benzoquinone /hydroquinone in polyamide selective layer of NF/RO membranes characterized by electrochemical impedance spectroscopy and filtration setup

The objective of this research was the study of benzoquinone/hydroquinone (Bq/BqH2) transport in polyamide selective layer of commercially available nanofiltration (NF) and reverse osmosis (RO) membranes using two methods ; electrochemical impedance spectroscopy (EIS) and filtration setup.The electrochemical experiments were carried out using a three-electrode cell containing about 50 cm3 of solution (Metrohm) with a selective polyamide layer isolated on the glassy carbon (GC) working electrode (A=0.07 cm2). The free polyamide fi lm was obtained in a way that the non-woven fabric was carefully peeled off to leave only the polysulfone and polyamide layers. Then, the electrode tip was dipped in N, N- dimethyl formamide (DMF) and immediately used to gently touch the polyamide surface of an about 1 cm2 piece of a membrane without non-woven, so that the piece stuck to the tip. The tip was then turned up and slowly washed with DMF to dissolve the polysulfone. The surface area of the investigated membranes in filtration setup was 10.8 cm2. Concentrations of the Bq and BqH2 before and after the membrane were measured by Total Organic Carbon Analyzer Shimadzu TOC-WVS. The permeability ω depended on concentration c, of Bq and BqH2, can be evaluated by filtration experiments of fitting flux vs rejection plots corrected for the concentration polarization for three different feed concentration and six fluxes to numeric solution of the modified Spiegler-Kedem equation. The aim is also to verify potential usage or non usage of Bq/BqH2 redox couple in EIS of isolated thin film and try to split ω to diffusion coefficient D and partition coefficient K. An indirect method based on selective solutes (markers) permeation data has been also used for determination of pore size and pore size distribution (PSD) in the membrane’ s selective layer in order to see how does the sieving effect influence the membrane exclusion mechanism of Bq/BqH2.

NF/RO membrane; electrochemical impedance spectroscopy; benzoquinone/hydroquinone (Bq/BqH2)

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