(288f) Alignment and Immobilization of Functionalized Aquaporins on Polybenzimidazole Nanofiltration Membranes

The overarching objective of this project is to form a biomimetic membrane incorporated with functional aquaporins dispersed in a polymeric membrane selective layer and capable of operation under high hydraulic pressure. Polybenzimidazole (PBI) membranes were surface modified with mutated aquaporins in order to improve the rejection of protons, ions and other impurities, aquaporin channels were aligned with the direction of water flow. Cysteine functional groups were installed on N-terminus of AqpZ (now called Aqp-SH) for covalent attachment to the polymer matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Modified membranes showed lower MWCO as compared to unmodified membranes. Depth profiling using XPS analysis showed the presence of functional groups corresponding to mutated aquaporins in modified membranes. FTIR analysis showed confirmation of an amphiphilic polymer (PVA-alkyl) which was used to seal the gaps in between protein molecules immobilized onto the membrane surface.

In agreement with pore size distributions, charge interactions, and added resistance to flow due to modification, as the pore size of the PVA-alkyl membranes decreased as compared to unmodified PBI membranes, the flux values were lower while salt rejection was higher. On the other hand, Aqp-SH modified membranes had a similar pore size to unmodified PBI membranes, but with the added resistance to flow, displayed lower flux values as compared to unmodified PBI but higher as compared to PVA-alkyl modified membranes. Furthermore, contrary to expectations due to pore size distributions, Aqp-SH modified membranes displayed the highest salt rejection values among all membranes analyzed in the study. Aqp-SH modified membranes displayed a nearly constant salt rejection irrespective of the salt concentration of the feed solution, while unmodified PBI and PVA-alkyl modified PBI membranes showed a decrease in rejections as feed salt concentration increased. However, due to the hindrance of detergent or PVA-alkyl in aquaporin solutions, the surface of the membrane was not completely covered with immobilized and aligned aquaporins, which in turn led to rejection values lower than 100%. If the concentration of functional aligned aquaporins on the membrane surface could be optimized, the performance of membranes could be further be improved.