Nafion-Based Low-Hydration Polyelectrolyte MultilayerMembranes for Enhanced Water Purification

摘要

The increase of micropollutant concentration in both surface and groundwater is an emerging concern for the environment and human health. Most of such small organic molecules (medicines, hormones, and plasticizers) enter the environment via our wastewater, because they are not sufficiently removed by the current techniques applied in wastewater treatment plants. A possible solution to remove micropollutants is the usage of polyelectrolyte multilayer (PEM) based membranes. PEM membranes have received a growing interest in the past decade due to their high chemical and physical stability and their high permeability and selectivity. A popular polyelectrolyte pair to make dense PEM membranes with high salt retentions is the combination of poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS). Unfortunately, smaller micropollutants (such as bisphenol A, sulfamethoxazole, naproxen, and bezafibrate) still show significant permeation through this membrane. In this study, for the first time, a single final layer of Nafion is applied on the PEM to increase the density of the PEM membrane.It is shown that when terminating with Nafion, the swelling of themultilayer decreases by 50%. These pronounced changes in layer structureare reflected by changes in membrane performance, such as a lowermolecular weight cutoff (MWCO) and an increasing hydraulic membraneresistance. Furthermore, we show that the Nafion content of the multilayercan be increased by constructing a Nafion/PAH multilayer on top ofthe existing PSS/PAH multilayer, thereby lowering the MWCO. Althoughhydraulic resistance increases, these PSS/PAH/Nafion-based multilayersshow excellent performance in rejecting difficult-to-remove micropollutantsthat have low molecular weight (200–650 Da) and different charges.Overall, a cocktail of eight small micropollutants can be removedup to 97% by these membranes, allowing strongly enhanced water purification.