Fabrication and Characterization of Micro-patterned Porous Membranes Using Hydrogel Facilitated Phase Separation Method
Creators: Asad Asad
Publisher: name: University of Alberta Library
Year: 2022

<p>Membrane separation processes are now well-established technologies in a wide range of applications, including biotechnology, pulp and paper, pharmaceutical, food processing, petroleum, wastewater treatment, and seawater desalination. The main challenges in membrane separation processes are (i) flux decline due to membrane fouling and (ii) the trade-off relationship between permeability and selectivity of a membrane. Membrane fouling is defined as the attachment of fouling materials (water contaminants) on the membrane surface and inside its pores, resulting in an overall reduction of the membrane performance with time and reducing its life span. Furthermore, membranes with high permeability (how fast the desired molecule to pass through a membrane) typically show a low rejection (how selective a membrane is to a desired molecule compared with the rest). The current methods to increase the membrane performance rely on chemical and physical approaches such as coating the membrane with hydrophilic/hydrophobic layers or modifying the membrane matrix through blending with additives (nanofillers, surfactants, and polymeric additives). However, these approaches have some severe disadvantages and limitations, such as the leaching of additives and coated materials during filtration, which affect the membrane performance, as well as the environmentally unfriendliness of utilized chemicals. Surface patterning has been proven to be an effective method to enhance membrane performance by increasing the effective surface area, which is directly proportional to the permeate flux. <br>
In this work, I presented a novel method to directly apply micro-scale patterns on the membrane surface using hydrogel facilitated phase separation (HFPS). A Hydrogel mold initiates the phase separation spontaneously when it contacts the polymer solution and this ensures that the location of the dense skin layer is on the patterned side. With this method, the active surface area of a membrane is larger than the equivalent flat surface that subsequently enhances water flux without a need to change the membrane surface chemistry. Fouling experiments with Bovine Serum Albumin (BSA) solution showed an increase in the flux for the patterned membrane after 100 min operation, demonstrating the advantage of using microstructure membrane for filtration applications.<br>
In the second phase of this research, I demonstrated, for the first time, a simple treatment process that allows repeated usage of the same hydrogel mold in micropatterned phase separation membrane castings. The method consists of warm and cold treatment steps to provide organic solvent extraction from hydrogel without changing the mold integrity. The best recovery result was 96%, which was obtained by placing the hydrogel in a warm water bath (50 ºC) for 10 minutes followed by immersing in a cold bath (23 ºC) for 4 minutes and finally 4 minutes drying in air. <br>
In the third phase, I prepared novel polyamide-imide (PAI) microfiltration membranes using our recently developed HFPS and Non-solvent induced phase separation (NIPS) techniques. The prepared membranes, including HFPS-patterned, HFPS-unpatterned, and NIPS, showed high porosity, superhydrophilicity, and underwater superoleophobicity. The underwater oil contact angles of n-hexadecane and mineral oils were higher than 150°, while a complete repellency for diesel oil was observed for all membranes. The ultra-high-water flux of patterned HFPS membranes, 440 Liter meter-2 hour-1 (LMH), made them outstanding candidates for separating oil/water emulsions. For all fabricated membranes, gravity-driven filtration experiments of 9 consecutive oil cyclic filtration tests yielded &gt; 99.9% oil removal efficiency. Moreover, after 18 filtration experiments, the flux recovery ratio and flux decline were in the range of 90-100 % and 3-20 %, respectively. <br>
In the fourth phase, I fabricated novel micropatterned thin-film composite (TFC) NF membranes using a two-step process. First, Hydrogel facilitated phase separation (HFPS) method was used to prepare micropatterned polyethersulfone (PES) substrate. Second, a thin dense polyamide (PA) film was formed on top of the PES substrate using interfacial polymerization reaction between piperazine (PIP) and trimesoyl chloride (TMC) monomers. TFC patterned membrane with 0.25 wt.% PIP showed ~96% increase in the water flux compared with an unpatterned one with only less than 10% reduction in the separation performance for different salts (e.g., MgSO4, Na2SO4, and NaCl), reactive black 5 dye, methyl orange dye and the treatment of real oil sands produced water due to the increase in the surface area.</p>