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We report a facile method for the antimicrobial modification of a thin-film composite polyamide reverse osmosis (RO) membrane. The membrane surface was first coated with polydopamine (PDA), whose reducing catechol groups subsequently immobilized silver ions in situ to form uniformly dispersed silver nanoparticles (AgNPs) inside the coating layer. Agglomeration of AgNPs was not observed despite a high silver loading of 13.3 ± 0.3 μg/cm(2) (corresponding to a surface coverage of 18.5% by the nanoparticles). Both diffusion inhibition zone tests and colony formation unit tests showed clear antimicrobial effects of the silver loaded membranes on model bacteria Bacillus subtilis and Escherichia coli. Furthermore, the silver immobilized membrane had significantly enhanced salt rejection compared to the control PDA coated membrane, which is attributed to the preferential formation of AgNPs at defect sides within the PDA layer. This self-healing mechanism can be used to prepare antimicrobial RO membranes with improved salt rejection without scarifying the membrane permeability, which provides a new dimension for membrane surface modification.

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Endocrine-disrupting compounds (EDCs), an important class of micropollutants with potent adverse health effects, are generally poorly rejected by traditional thin film composite polyamide membranes and thus pose significant risks in membrane-based water reclamation. We hypothesize that membrane rejection of hydrophobic EDCs can be enhanced by a hydrophilic surface coating. Using polydoamine (PDA) as a model hydrophilic coating layer, the PDA-coated NF90 membrane experienced an up to 75% reduction in the passage of bisphenol A compared to the control (NF90 without coating). Meanwhile, we also observed a systematic increase in the level of rejection of three hydrophobic parabens with an increase in PDA coating time. In contrast, there were no systematic changes in the rejection of neutral hydrophilic polyethylene glycol, which suggests that the enhanced rejection of EDCs was due to weakened EDC− membrane hydrophobic interaction. Further sorption tests revealed that the hydrophilic PDA coating could effectively decrease the rate of sorption of EDCs by the membrane, which is responsible for the improved rejection as predicted by the solution− diffusion theory. This study reveals an exciting opportunity for engineering membrane surface properties to enhance the rejection of targeted micropollutants, which has important implications in membrane-based water reclamation.

We report a fast, simple, and green coating method using the coordination complex of tannic acid (TA) and ferric ion (Fe) to enhance the removal of trace organic contaminants (TrOCs) by polyamide membranes. The entire coating process can be completed in less than 2 min; quartz crystal microbalance characterization revealed that a TA-Fe thin film formed in merely 10-20 s. Coating this TA-Fe thin film on a commercial nanofiltration membrane (NF270) reduced its effective pore size from 0.44 to 0.40 nm. The TA-Fe-coated NF270 showed significantly increased rejection of both NaCl and trace organic contaminants. In comparison with the more-time-consuming polydopamine coating (e.g., 0.5 h), the TA-Fe coating presented greater resistance to TrOC permeation (i.e., lower permeability of TrOCs). The advantages of the fast coating process, greatly improved rejection performance, and use of green accessible materials make TA-Fe a highly promising coating material for large-scale applications.