(686d) Dual-Functionalized Nanofiltration Membranes Exhibit Multifaceted Anti-Fouling and Ion Rejection Performance

As interest in decentralized water treatment units that enable localized water reuse grows, the development of nanofiltration (NF) membranes as a complementary technology to reverse osmosis membranes has gained traction. Furthermore, the use of advanced materials (e.g., graft copolymers), which form uniform nanoscale pores that are decorated with tunable chemical moieties can provide a ready means for post-assembly functionalization. For example, the incorporation of charged functionalities increases ion rejection by NF membranes due to repulsive electrostatic interactions. However, the incorporation of charge functionality tends to exacerbate the process of fouling, which is a continued hurdle in the development and application of NF membranes. Fouling is the process whereby attractive dispersive, electrostatic, and hydrodynamic interactions between dissolved solutes and the membrane leads to the attachment and accumulation of material on the surface of the membrane. This process reduces the throughput and performance of the membrane. This study evaluates novel NF membranes that exhibit both high ion rejection and high fouling resistance through the use of a post-fabrication multi-functionalization process performed on the membrane template.

Membranes cast from a poly(acrylonitrile-co-oligo-(ethylene glycol) methyl ether methacrylate-co-(3-azido-2-hydroxypropyl methacrylate)) P(AN-OEGMA-AHPMA) copolymer are the parent substrates utilized in this study. The azido groups lining the pore wall of the parent substrate lead to multiple functionalization avenues. Here, a dual functionalized membrane containing both ion-selective and anti-fouling functionality is attained through a controlled reaction between propiolic acid and the membrane. This copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction occurs rapidly and by varying the concentration and the exposure time the penetration depth of the initial reaction can be controlled. This control is confirmed through a decrease in the signal intensity associated with the azido group in the Fourier transform infrared spectroscopy (FTIR) spectrum. This layer achieves an anti-fouling character through a 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) coupling reaction of 1H,1H-perfluorooctylamine with the propiolic acid. The azido moieties not exposed to propiolic acid in the initial stage are then charge-functionalized through a CuAAC reaction of propargyl amine. When challenged with a 0.5 g/L Bovine Serum Albumin (BSA) solution, these membranes express increased anti-fouling properties compared to a fully charged membrane, while maintaining similar ion rejection performance.

This study begins the analysis of incorporating multiple, useful functionalities into a single membrane template. The rapid exposure of a reactive solution works to prove that through readily controllable reactions, the required depth for inhibiting foulant interactions could be reduced down to the minimal distance in which the attractive forces between the foulants and the surface is shielded. Minimizing this layer incorporates more charged-groups on the pore wall, increasing the overall resistance to ion-transport. This membrane fabrication process can be further extended to ion-exchange membranes, in which the inclusion of a top surface anti-fouling layer could increase the lifespan of the membrane while maintaining a high ionic throughput.