<p>Metal-organic frameworks (MOFs) are considered as a type of very useful materials for the gas separation/purification industries. However, control over the growing position and growing shape of the crystals remains a challenge and must be overcome in order to realize the commercial potentials of MOFs.</p> <p>In this thesis, a method based on interfacial coordination is developed to address this issue. Zinc-benzenedicarboxyl (Zn-BDC) is chosen as a model system for the proof of concept. In a typical liquid-liquid interface protocol, the MOF precursors, zinc nitrate [Zn(NO3)2] and terephthalic acid (TPA or H2BDC), and the catalyst, triethylamine (TEA), were dissolved into two immiscible solvents, dimethylformamide (DMF) and hexane, respectively. The reaction site, i.e. the MOF growing position could thereby be confined at the interface of the two solvents. It was found that a free-standing membrane could be formed with the combinations of high Zn-H2BDC and low TEA concentrations. The combinations of low Zn-H2BDC and high TEA concentrations yielded MOF particles precipitated out from DMF. Similar results were obtained by changing the liquid-liquid interface to liquid-gas interface, with the TEA-hexane solution replaced by saturated TEA vapor. The dependence of product shape on precursor and catalyst concentrations can be explained by the competition between MOF formation and TEA diffusion into the precursor phase.</p> <p>The morphology, constitution and surface area of the MOF products were characterized by SEM, XRD and nitrogen adsorption testing, respectively. The particles were found to be exclusively MOF-5. The membranes were characterized as asymmetric. The top layer was particulate while the bottom layer had a sheet-like morphology. This was further revealed by XRD data as MOF-5 and MOF-2 (ZnBDC·DMF), respectively. This asymmetry was caused by a change of TEA diffusion rate during the synthesis process, which might result in a change in pH value for the membrane growth. Decent surface areas of the particles and membranes were measured.</p> <p>Apart from the free-standing membranes, MOF membranes on Anodisc support were also synthesized employing the same interfacial techniques. The MOF formation site, i.e. the interface, was confined to the upper end Anodisc pores and sealing the pores after the reaction. The difference in wetting force between DMF and hexane with Anodisc membrane material resulted in the difference of MOF layer morphology from liquid-liquid protocol and liquid-gas protocol. The later gave a continuous MOF membrane due to the absence of air bubble interference.</p> / Master of Science (MSc)

<p>Membrane filtration is widely used to biomedical and analytical applications. Compared to other techniques available membrane filtration provides fast processing time, easy availability, robust performance and relatively low cost. These advantages make ultrafiltration and microfiltration well integrated into bioseparation, purification of biomedical materials and downstream polishing. Apart from the advatanges, there are certain drawbacks with microfiltration and ultrafiltration. While perceived negative in many scenarios, the effects does not necessarily counteract the purpose of the process and could find some useful applications if treated from a different perspective.</p> <p>By the virtue of fast processing of membrane filtrations, applications were made in processing biomedical materials and developing analytical methods. Poly(<em>N</em>-isopropylacrylamide) microgels are of potential in many biomedical applications. Microfiltration and ultrafiltration of such microgels for fast purification were explored. Meanwhile, the environmental responsive behaviours of such microgels bring about opportunity and challenge. Investigations were made on the salt-responsive transmission behaviours of microgels in microfiltrations. A hypothesis was raised and verified. Implications of applications <em>in vivo</em> were drawn based on experimental results. Many techniques for analysis of protein-drug binding have been under development. A new alternative utilizing pulsed tangential flow ultrafiltration was developed in this study and used to obtain binding data between aspirin and BSA under different conditions. The performance of the systems was assessed under different parameter settings. Possibility of further automation was discussed. On account of the fouling and concentration polarization, a new perspective was taken with the effort of developing such effects into potential applications. Patterned fouling was introduced and the fouled membrane was used to filter coloured feed to reveal the patterns transferred. Concentration polarization in ultrafiltrations with different levels of fixation of membranes was visualized by dyed particles. The possible flow modes under these conditions were suggested. A hypothesis was attempted from a fluidics point of view.</p> / Master of Applied Science (MASc)

<p>Nanofiltration (NF) is a pressure-driven membrane separation process, which is a nonequilibrium process because of the pressure difference and concentration difference across the membrane. As one type of molecular dynamics (MD) simulations, nonequilibrium molecular dynamics (NEMD) simulations can provide the dynamics properties of NF transport on a molecular level description, which can serve as a complement to conventional experimental studies.</p> <p>In this thesis, NEMD simulations are proposed to study pressure-driven liquid flows through carbon nanotube (CNT) membranes and polyamide (PA) membranes at realistic NF conditions. Pure water flows passing through the membranes are studied primarily, and organic flows passing through the CNT membranes are also studied. Little research, that we are aware of, has been done to show the NF transport properties. The results of the NEMD simulations are analyzed to investigate the transport properties and the effects of the membrane structures on liquid transport, and the simulation results are compared with traditional models and/or literature data. This work shows that show that the liquid transport through the CNT membrane is extremely fast and cannot be predicted by the continuum equations due to the special properties of the CNT, and the water transport of the PA membrane is strongly related to the free-volume properties of the amorphous polymeric membrane.</p> <p>The MD simulation studies proposed in this thesis are feasible as a tool for describing and investigating pressure-drive liquid transport and can provide some fundamental basis for NF transport.</p> / Doctor of Philosophy (PhD)

<p>Endocrine disrupting substances have been frequently reported to exist in potent concentrations in wastewater treatment plant effluent and other surface waters. Common techniques of wastewater treatment have varied effectiveness to remove estrogens from wastewater. A thermo-responsive smart membrane technology is investigated for its use in adsorptive removal of 17β-estradiol from a background electrolyte solution. A simplified fabrication method is adapted for hydrogel-substrate composite thermo-responsive membranes. Deposition of hydrogel occurs through aqueous polymerization in a coating process dissimilar to common grafting techniques. Acrylamide and acrylic acid monomers are polymerized in two different structures, a random copolymer as well as an interpenetrating network, to form a positive volume-phase transition hydrogel coating. Subsequent membranes experience high permeability at low temperatures with a gating mechanism reducing permeability upon heating. The effects of crosslinker content, monomer ratio, mass loading and butylmethacrylate content are investigate. Only mass loading was found to have significant influence on the behaviour of the membranes in all cases. The variations of the other factors were too little to have great influence. The membranes with the most stable permeability response function were then used in 17β-estradiol adsorption tests, investigating the binding capacity at both colder water temperatures (10oC) and warmer water temperatures (40oC). In the collapse and swelling of the volume-phase transitions, the membranes changed their solution properties which were hypothesized to also alter surface functionality. After introducing the estradiol sample, the membranes were subjected to temperature change with the expectation that any bound material would elute once the surface functionality of the membranes became adequately altered. Only some membranes produced an elution fraction while others appeared to undergo irreversible binding with a possible delayed elution. Removal of dosed 17β-estradiol is reported as adsorbed mass per area of membrane.</p> / Master of Applied Science (MASc)

Gram-negative bacterial cells are surrounded by a cell membrane which protects the cell and controls the transport of nutrients and waste products in and out of the cells at a fast rate. This rapid transport of nutrients and wastes through the cell membrane is made possible by channel proteins called porins. Various types of porins present in the cell membrane have specific functions depending on their selectivity towards different nutrients, and channel proteins selective towards water are called aquaporins. These proteins restrict the passage of all entities except water molecules and they provide a fast transport rate of water molecules at 109 molecules/second per channel. The high selectivity of porins has led to their incorporation into synthetic systems, and one example is the addition of porins to separations membranes in order to enhance their performance in terms of selectivity and permeability, in a field called biomimetics. The concept of incorporating aquaporins into synthetic membranes has been studied for the last 10 years in order to enhance the water permeability and selectivity of membranes for water purification; however, there are still limitations such as high costs, difficulties in fabrication of aquaporins, their alignment into synthetic membrane assembly, low stability, and limitations on number of aquaporin molecules that can be introduced into synthetic membranes limit their applicability. In recent years, concurrent with the work on aquaporin-based biomimetic membranes, there has been an increase in the study of synthesizing molecules with similar structure-function relationships of aquaporins. These artificial channels attempt to mimic the high-water permeability and selectivity of aquaporins, while being synthesized using simple chemistry, being solvent compatible, and requiring less space on the membrane surface which helps to incorporate more channels into the membrane assembly. The objectives of this study were to first incorporate aquaporins into synthetic nanofiltration membranes without chemical alteration them to prevent flattening or denaturing of aquaporins; then, the second objective was to install functional groups on aquaporins and align them in the direction of water flow; lastly, the third objective was to synthesize artificial channels in order to overcome the issues with aquaporin stability, alignment, and efficient packing of water channels onto the membrane surface. For the first objective, aquaporins were treated with a polysaccharide, gum Arabic, and incorporated into an amphiphilic polymer, polyvinyl alcohol with alkyl side chains (PVA-alkyl), in order to simulate the natural housing of lipid bilayer for aquaporins and to protect them from denaturing. Long alkyl chains provided the hydrophobic component, while PVA provided the hydrophilic component of the amphiphilic polymer. Membranes modified with aquaporins displayed lower flux declines and higher flux recoveries after reverse flow filtration, along with improved rejection values for both protein and salt solutions as compared to PBI and PBI-PVA-alkyl membranes. However, there was leakage of ions between channels. Therefore, in order to improve the rejection of protons, ions and other impurities, the channels were aligned with the direction of water flow. Functional groups were installed on Aquaporins using site-directed mutagenesis for covalent attachment to the polymer matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the flow. Aquaporin constructs were modified to bear affinity tags or unique amino acids at the N-terminus of the aquaporin molecule, which was used to facilitate directional immobilization. Each aquaporin monomer was modified with a unique amino acid Cys group at the N-terminus right after the first Met, and due to the aquaporin tetrameric nature, these Cys groups became four anchors for attachment. The presence of these four Cys anchors per aquaporin tetramer was used to attach on the membrane surface in alignment with the feed water flow direction. Membranes modified with mutated aquaporins showed consistently higher salt rejection values of ~70% irrespective of feed concentration, along with higher flux recoveries and lower flux declines. Commercial NF-270 membranes provide a monovalent salt (NaCl) rejection of ~50% and divalent salt (MgCl2) rejection of 97%. Also, approximate coverage of membrane surface with attached aquaporins was calculated using simulation studies. Simulation studies showed that immobilized aquaporins with PVA-alkyl provided a diffusion rate equivalent to 64% coverage on the membrane surface. This showed that aquaporins didn’t cover the entire surface area of the membrane. However, immobilized aquaporins were responsible for the rejection of a portion of ions passing through the membrane. In order to overcome the limitations of aquaporin incorporation into polymer membranes, artificial organic frameworks were added as surface modification on PBI membranes. Organic frameworks were synthesized as derivatives of hybrid bisamides. The series of bisamides 1-4 consist of 6-amino-pyridine-2-dicarboxylic acid, 6-hydroxymethyl-pyridine-2-carboxylic acid and ethylenediamine, trimethylenediamine, putrescine, and cadaverine depending on the length of carbon chain. These frameworks are amphiphilic in nature and have strong chemical attachment due to the presence of amines and carboxylic acids into each building block. These molecules were introduced into the membrane matrix using carbodiimide chemistry. FTIR results showed the attachment of these bisamide molecules onto the surface of a modified PBI membrane. Also, modified membranes showed a reduced molecular weight cut off (MWCO) for neutral organic molecules. Overall, membranes modified with aquaporins have shown a potential to provide consistently high salt rejections with increasing feed solutions. Also, preliminary results have shown that bisamide molecules can be attached onto the membrane surface as organic frameworks and have a potential to be an alternative for aquaporins based biomimetic membranes.

Mixed matrix membranes (MMM) offer one potential path toward exceeding the Robeson upper bound of selectivity versus permeability for gas separation performance while maintaining the benefits of solution processing. Many inorganic materials, such as zeolites, metal-organic frameworks, or carbon nanotubes, can function as molecular sieves, but as stand-alone membranes are brittle and difficult to manufacture. Incorporating them into a more robust polymeric membrane matrix has the potential to mitigate this issue. In this work, phase inversion polymer solution processing for the fabrication and testing of asymmetric flat sheet mixed matrix membranes was employed with CVD-derived multiwall carbon nanotubes (MWCNTs) dispersed in a polyethersulfone (PES) matrix. The effect of MWCNT loading on membrane separation performance was examined. Notably, a distinct enhancement in selectivity was measured for several gas pairs (including O2/N2) at relatively low MWCNT loading, with a peak in selectivity observed at 0.1 wt% loading relative to PES. In addition, no post-treatment (e.g. PDMS caulking) was required to achieve selectivity in these membranes. In contrast, neat PES membranes and those containing greater than 0.5 wt.% MWCNT showed gas selectivity characteristic of Knudsen diffusion through pinhole defects. These results suggested that at low loading, the presence of MWCNTs suppressed the formation of surface defects in the selective layer in flat sheet mixed matrix membranes. Additionally, a bench-scale, single-filament hollow fiber membrane spinning line was designed and purpose-built at the University of Kentucky Center for Applied Energy Research (CAER). Hollow fiber membrane spinning capability was developed using polyethersulfone (PES) solution dopes, and the process was expanded to include polysulfone (PSf) as well as mixed matrix membranes. The effects of key processing parameters, including the ratio of bore to dope velocities, the spinning air gap length, and the draw-down ratio, were systematically investigated. Finally, direct hollow fiber analogues to flat sheet mixed matrix membranes were characterized. Consistent with the flat sheet experiments, the mixed matrix hollow fiber membranes showed a local maximum in selectivity at a nominal loading of 0.1 wt.% MWCNT relative to the polymer, suggesting that the pinhole suppression effect introduced by MWCNTs was not limited to flat sheet membrane casting. The development of asymmetric hollow fiber mixed matrix membrane processing and testing capability at the UK Center for Applied Energy Research provides a platform for the further development of gas separation membranes. Using the tools developed through this work, it is possible to further push the frontiers of mixed matrix gas separation by expanding the capability to include more polymers, inorganic fillers, and post treatment processes which previously have been focused primarily on the flat sheet membrane geometry.

Future nanofiltration (NF) membranes used for selective separations of ions and small organic molecules must maintain performance in environments where high concentrations of total dissolved solvents or foulants are present. These challenges can be addressed through the development of composite membranes, as well as the engineering of enhanced surface properties and operating conditions for existing commercial membranes. In this work, ion transport through commercial thin film composite (TFC) polyamide NF membranes were studied in both lab-prepared salt solutions and industrial wastewater. The dependence of several variables on ion rejection was investigated, including ion radius, ion charge, ionic strength, and temperature. The impact of scaling and increasing ionic concentration on membrane performance during recovery of industrial wastewater was investigated. Fouling of the membrane surface was reduced by enhancing commercial NF membrane surfaces via aqueous-phase esterification of lignin sulfonate. NF membranes were also created utilizing an ionic liquid solvent (1-ethyl-3-methylimidazolium acetate) to integrate composite materials into cellulose. Composite materials such as graphene oxide quantum dots, iron III particles, and lignin have been shown to be interact strongly with cellulose in solution with ionic liquid and bind together cellulose chains via hydrogen bonds following nonsolvent induced phase inversion. Studies suggest the composite materials modify membrane surface chemistry and improve selectivity of small organic molecules (~300 nm) while allowing for the complete passage of ions.

Automated and continuous processes are the future trends in downstream protein purification. A functionalized nanometer-scale membrane electrode system, mimicking the function of cell wall transporters, can selectively capture genetically modified proteins and subsequently pump them through the system under programmed voltage pulses. Numerical study of the two-step pulse pumping cycles coupled with experimental His-GFP releasing study reveals the optimal 14s/1s pumping/repel pulse pumping condition at 10 mM bulk imidazole concentration in the permeate side. A separation factor for GFP: BSA of 9.7 was achieved with observed GFP electrophoretic mobility of 3.1×10-6 cm2 s-1 V-1 at 10 mM bulk imidazole concentration and 14 s/1 s pumping/repel duration. The purification of His6-OleD Loki variant directly from crude E. coli extracts expression broth was demonstrated using the pulse pumping process, simplifying the separation process as well as reducing biopharmaceutical production costs. The enzymatic reactions showed that His6-OleD Loki was still active after purification. A nanoporous membrane/electrode system with directed flow carrying reagents to sequentially attached enzymes to mimic nature’s enzymes-complex system was demonstrated. The substrates residence time on the immobilized enzyme can be precisely controlled by changing the pumping rate and thereby prevent a secondary hydrolysis reaction. Immobilized enzyme showed long term storage longevity with activity half-life of 50 days at 4℃ and the ability to be regenerated. One-step immobilization and purification of His-tagged OleD Loki variant directly from expression broth, yielded 98% Uridine Diphosphate glycosylation and 80% 4-methylumbelliferone glycosylation conversion efficiency for the sequential reaction. A flow-through electroporation system, based on a novel membrane/electrode design, for the delivery of membrane-impermeant molecules into Model Leukocyte cells was demonstrated. The ability to apply low voltage between two short distance electrodes contributes to high cell viability. The flow-through system can be easily scaled-up by varying the micro-fluidic channel geometry and/or the applied voltage pulse frequency. More importantly, the system allows the electrophoretical pumping of molecules from the reservoir across the membrane/electrode system to the micro-fluidic channel for transfection, which reduces large amount of reagents used.

Membrane process including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) have provided numerous successful applications ranging from drinking water purification, wastewater treatment, to material recovery. The addition of functional moiety in the membranes pores allows such membranes to be used in challenging areas including tunable separations, toxic metal capture, and catalysis. In this work, polyvinylidene fluoride (PVDF) MF membrane was functionalized with temperature responsive (poly(N-isopropylacrylamide), PNIPAAm) and pH responsive (polyacrylic acid, PAA) polymers. It’s revealed that the permeation of various molecules (water, salt and dextran) through the membrane can be thermally or pH controlled. The introduction of PAA as a polyelectrolyte offers an excellent platform for the immobilization of metal nanoparticles (NPs) applied for degradation of toxic chlorinated organics with significantly increased longevity and stability. The advantage of using temperature and pH responsive polymers/hydrogels also includes the high reactivity and effectiveness in dechlorination. Further advancement on the PVDF functionalization involved the alkaline treatment to create partially defluorinated membrane (Def-PVDF) with conjugated double bounds allowing for the covalent attachment of different polymers. The PAA-Def-PVDF membrane shows pH responsive behavior on both the hydraulic permeability and solute retention. The sponge-like PVDF (SPVDF) membranes by phase inversion were developed through casting PVDF solution on polyester backing. The SPVDF membrane was demonstrated to have 4 times more surface area than commercial PVDF MF membrane, allowing for enhanced nanoparticles loading for chloro-organics degradation. The advanced functionalization method and process were also validated to be able to be scaled-up through the evaluation of full-scale functionalized membrane provided by Ultura Inc. California, USA. Nanofiltration (NF) between UF and RO presents selectivity controlled by both steric and electrostatic repulsions, which are widely used to reject charged species, particularly multivalent ions. In this work, selective permeation of CaCl2 and high sucrose retention are obtained through the modification of nanofiltration membranes with lower charge compared to commercial nanofiltration membrane. The membrane module also shows high stability with constant water permeability in a long-term (two months) test. Extended Nernst-Planck equation were further used to evaluate the experimental results and it fits well.

The development of functionalized membranes with tunable pores and catalytic properties provides us an opportunity to manipulate the membrane pore structure, selectivity and reactivity. By introducing the functional groups into membrane pores, dissolved metal ions and reactive particles can be effectively immobilized within the polymer matrix for toxic chloro-organic and heavy metal remediation in water. A polyelectrolyte functionalized membrane platform with tunable pore size and ion exchange capacity has been developed for iron/iron oxide nano-catalyst synthesis and chlorinated organic compound (trichloroethylene, TCE and polychlorinated biphenyls, PCBs) degradation. Highly robust polyvinylidene fluoride (PVDF) microfiltration membranes are used as the support with cross-linked polyacrylic acid (PAA) filled in the pores. By varying the environmental pH, PAA hydrogels have either swelling or collapsing behavior, resulting in different effective membrane pore sizes for different separation purposes. Cation exchange groups (i.e. carboxyl groups) in PAA chains prevent the aggregation and leaching of nanoparticles (NPs) during in-situ synthesis and reaction. Depending on the catalyst loading and residence time, TCE and PCBs can be completely degraded by reduction of zero-valent iron and bimetallic iron/palladium NPs, or iron oxide catalyzed free radical oxidation at near-neutral pH. Biphenyl from PCB dechlorination can be further oxidized by hydroxyl radicals (OH•) generated from hydrogen peroxide (H2O2) decomposition. Hydroxybiphenyls and benzoic acid are identified as oxidation products. Line scan and elemental mapping in transmission electron microscopy (TEM) and X-ray photo electron spectroscopy (XPS) characterizations are conducted to understand the effect of iron surface transformation on NP reactivity, and to optimize the membrane functionalization. The same platform can also be used to remove toxic metal selenium in the scrubber water of coal-fired power plants. By reducing the salt concentration in water or increasing the residence time and temperature, the concentration of selenium oxyanions in functionalized membrane permeate can be reduced to less than 10 µg/L. Selenium is captured in membranes by both iron reduction to metallic selenium and iron oxide adsorption. The full-scale flat sheet functionalized membrane and spiral wound modules have also been developed. Iron NPs with alterable loadings are successfully synthesized inside the membrane module for real water applications.