Permselective Permselective Membranes Composed of Two-dimensional Polymers with Tailorable Separation Properties through Host-guest Chemistry
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Separation of small molecules is of great interest in industries, especially for pharmaceutical and biological applications. However, traditional separation method, such as chromatography, is difficult to achieve in large industrial scale. The membranes that can perform separations by size, hydropho...
- Separation of small molecules is of great interest in industries, especially for pharmaceutical and biological applications. However, traditional separation method, such as chromatography, is difficult to achieve in large industrial scale. The membranes that can perform separations by size, hydrophobicity, charges and other chemical properties may provide a scalable, recyclable, energy efficient, easy to operate separation method for industries. Membranes with nanometer-scale features have been explored in areas such as catalysis, selective molecule separation, ﬁltration and puriﬁcation, biosensing and many others. However, fabrication of nanoporous membranes is still challenging regardless of the methods reported such as electroless gold deposition, atomic layer deposition, polymer self-assembly, and conformal initiated chemical vapor deposition, due to their complicated and lengthy manufacturing processes. Indeed, a simple, fast, and clean method for the fabrication of nanoporous membranes with tailorable surface properties will be useful for the growth of membrane technology.
In this thesis, a facile fabrication of permselective membranes using two-dimensional (2D) polymers and their tunable separation properties by host-guest chemistry is presented. 2D polymers composed of (allyloxy)12cucurbituril (AOCB), a hollowed-out pumpkin-shaped host molecule, and dithiol linkers are laterally grown macroscopic polymer films with a quasi-hexagonal network internal structures and single monomer thickness. These 2D polymers were synthesized easily in solution, and subsequently transferred onto the supporting membranes to fabricate the permselective membranes. By harnessing the interstitial spaces between adjacent AOCBs and “defect” sites of the films, size-selective separation of various analytes was demonstrated by simple filtration techniques. In order to tune the separation properties, the permselective membranes were modified in two different ways, and their separation abilities were studied as well. Modification of the 2D polymer was achieved either by attaching additional group in a covalent manner at the residual thiol groups of the 2D polymer using the thiol-ene click chemistry, or by introducing appropriate functional groups on the 2D polymer in a noncovalent manner through the host-guest interactions between the CB unit and guests. By these modifications, positive as well as negative charges, hydrophobic alkyl chains, and hydrophilic PEG chains were introduced into the 2D polymers, and the modified 2D films exhibited significantly improved selective filtration properties towards specific analytes, which was confirmed by filtration and osmosis experiments.