Industrialization, population growth and depleting energy resources have created an urgent need for efficient desalination. Among the various processes available, reverse osmosis (RO) is often considered the most energy-efficient technology.  Current thin film composite membranes used for RO contain a thin polyamide barrier layer placed onto an asymmetric support. These membranes suffer from drawbacks such as low flux, high pressure requirements and high fouling rates. Thus, to improve the permeability of RO membranes, electrospun nanofiber membranes (ENMs) as a support have great potential due to the high surface area to volume, high porosity and interconnected pore structure.<br/>Here we discuss our efforts to prepare thin film nanofibrous composite (TFNC) membranes by forming a selective layer on a polyacylonitrile (PAN) nanofibrous support by molecular layer-by-layer assembly (mLbL). In contrast to the traditional interfacial polymerization membranes, the thickness and chemical composition of the mLbL layer can be controlled by the number of deposition cycles and the sequence of the monomer building blocks used, respectively. In our preparation method, m-phenylenediamine and trimesoyl chloride were reacted sequentially to form a barrier polyamide layer on an electrospun nanofiber mat. In order to prevent the entry in to the nanofiber matrix, PAN nanofibers were spin coated with a thin layer of polyvinyl alcohol prior to mLbL deposition. To improve the selectivity of the RO process, laponite clay nanoparticles were also incorporated into the polyamide layer during the mLbL process. Incorporation of these nanoparticles into the barrier layer influenced the permeation of water molecules and the salt ion-water complex. The morphological changes of the PAN nanofiber were recorded by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The distribution of the laponite nanoparticles into the polyamide layer were studied by X-ray diffraction and Raman Spectroscopy. Transport tests were conducted to quantify the hydraulic permeability and solute rejection capabilities of these TFNC membranes. Fouling propensity of the membranes were studied by humic acid as the model foulant and fouled membranes were also analyzed by microscopic imaging.  A combination of material characterization and transport testing lays the groundwork for the development of structure-property-performance relationships that will guide the development of this new class of TFNC.<br/>

Electrospun nanofiber supported thin film composite membranes prepared by molecular layer-by-layer assembly

251st National Meeting (2016)

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