New and advanced opportunities are arising for the synthesis and functionalization of membranes with selective separation, reactivity, and stimuli-responsive behavior. One such advancement is the integration of bio-based channels in membrane technologies. By a layer-by-layer (LbL) assembly of polyelectrolytes, outer membrane protein F trimers (OmpF) or “porins” from Escherichia coli with central pores ∼2 nm in diameter at their opening and ∼0.7 × 1.1 nm at their constricted region are immobilized within the pores of poly(vinylidene fluoride) microfiltration membranes, in contrast to traditional ruptured lipid bilayer or vesicle processes. These OmpF-membranes demonstrate selective rejection of non-charged organics over ionic solutes, allowing the passage of up to 2 times more salts than traditional nanofiltration membranes starting with rejections of 84% for 0.4 to 1.0 kDa organics. The presence of charged groups in OmpF-membranes also leads to pH-dependent salt rejection through Donnan exclusion. These OmpF-membranes also show exceptional durability and stability, delivering consistent and constant permeability and recovery for over 160 h of operation. Characterization of the solutions containing OmpF and the membranes was conducted during each stage of the process, including detection by fluorescence labelling (FITC), zeta potential, pH responsiveness, flux changes, and rejection of organic–inorganic solutions.
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Funding: This work was supported by the National Science Foundation NSF KY EPSCoR program (Grant no: 1355438) and the National Institutes of Environmental Health Sciences NIEHS-SRC (grant number P42ES007380).
Electronic supplementary information (ESI) available: Detailed methods and analysis are illustrated in the ESI material. These include sections on functionalization and characterization of the OmpF solution and membrane; ζ potential procedures; preliminary characterization of the concentrations of feed retentate and permeate; membrane selection; optimization of PAA functionalization; FITC labelled OmpF analysis of the feed and permeate; model organic compound regressions; and material imbalance minimization. See DOI: 10.1039/c7ra08737c
Hernández, Sebastián; Porter, Cassandra; Zhang, Xinyi; Wei, Yinan; and Bhattacharyya, Dibakar, "Layer-by-Layer Assembled Membranes with Immobilized Porins" (2017). Chemical and Materials Engineering Faculty Publications. 29.