Capturing hormones and bisphenol A from water via sustained hydrogen bond driven sorption in polyamide microfiltration membranes

This work investigates the distinct sorption properties of polyamide 66 (PA) microfiltration membranes for estrogenic compounds in water. Four representative estrogenic endocrine disruptors, namely estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2) and bisphenol A (BPA), were readily captured from water via sustained sorption in PA microfiltration membranes during crossflow filtration. Such significant sorption was only observed on PA membranes among seven polymeric membrane materials tested, including polyethersulfone (PES), cellulose acetate (CA), mixed nitrocellulose (MCE), polyester (PETE), regenerated cellulose (RC), polycarbonate (PC), and PA. The strong binding affinity originates from the hydrogen bonding interactions between PA amide groups and the proton-donating moieties of the target compound molecules. For hormone compounds, a correlation was further identified between their proton-donating moieties and sorption capacities in PA membranes. Using 0.2 μM (46-59 μg L^-1) compound spiked solutions, the 0.2-μm PA membrane exhibited a sorption capacity of 81 L m^-2 (0.44 μg cm^-2) for E1, 150 L m^-2 (0.82 μg cm^-2) for E2, 208 L m^-2 (1.23 μg cm^-2) for EE2, and 69 L m^-2 (0.32 μg cm^-2) for BPA. The sorption capacity of PA membrane was largely unaffected by membrane flux or the co-presence of multiple target compounds or humic acid, but showed strong dependence on the membrane surface area and the compound concentration. The hydrogen bond driven sorption is a reversible process and desorption was effected by contacting exhausted PA membranes with 0.4 wt.% caustic solution at room temperature. The PA membrane exhibited consistent sorption capacities for the four target compounds in water through three cycles of reuse.