(527a) Advancing NF Membranes: Role of Surface Charge and Support

Nanofiltration (NF) membranes have been reported to selectively separate charged small molecules and ions providing a variety of applications, as for example rejection of negatively charged ions/molecules or recovery of valuable metals (multivalent cations), simultaneously reducing the osmotic pressure of the system by letting pass non-desired ions. Therefore, tuning and understanding the role of surface charge will allow better NF design as well as suitable applications.

Moreover, the ultrafiltration (UF) membrane as support for NF membranes has been reported to impact both the formation and performance of the NF layer. In this study, we use 3 different UF supports (two polyethersulfone (PES) and one polysulfone (PSf – commercial PS35), and we synthesize the NF layer by rapid interfacial polymerization using two (commercially available) amine groups: traditional negatively charged NF membrane with piperazine (PIP); and another with modified chemistry by addition of polyallylamine hydrochloride (PAH) – more positively charged.

It was observed an impact on the performance of the synthesized NF membranes from both differences in the substrate as well as by the addition of PAH, making them part of the variables (direct or indirect) of the final NF performance. An increase in the zeta potential (around 2 points in the isoelectronic point) of the membranes is obtained from the addition of PAH for all substrates used. Using latest theoretical approach of zeta potential calculations for composite with porous materials (as UF membranes), a more real estimation of the difference in surface zeta potential between NF membranes with and without PAH addition is calculated through an algebraic approach.

In terms of performance, on one hand, water permeabilities were affected: up to 7% decrease by addition of PAH, and a more significant decrease of 2 and 3 folds by varying support. On the other hand, rejection of salt increased: up to 20 – 30% points of PAH addition, and 20 – 40% from different support. Deep characterization of substrates, as well as the synthesized NF membranes (including modeled pore size), is performed for correlation with the mentioned variables.