Over the past few decades there has been great interest in exploring alternatives to conventional separation methods due to their high cost and energy requirements. Membranes offer a potentially attractive alternative as they potentially address both of these points. The overarching theme of this dissertation is to design nanocomposite membranes for processes where existing separation schemes are inadequate. This dissertation focuses on three challenges: 1) designing organic-inorganic hybrid membranes for reverse-selective removal of alkanes from light gases, 2) defect-free inorganic nanocomposite membranes that have uniform pores, and 3) nanocomposite membranes for minimizing protein fouling in microfiltration applications. Reverse-selective gas separations that preferentially permeate larger/heavier molecular species based on their greater solubility have attracted considerable recent attention due to both economic and environmental concerns. In this study, dendrimer-ceramic hybrid membranes showed exceptionally high propane/nitrogen selectivities. This result was ascribed to the presence of stable residual solvent that affects the solubility of hydrocarbon species. Mesoporous silica-ceramic nanocomposite membranes have been fabricated to provide defectless mesoporous membranes. As mesoporous silica is iteratively synthesized in the ceramic macropores, the coating method and the surfactant removal step significantly affected permeance and selectivity. It was also shown that support layers can cause a lower selectivity than Knudsen limit. Membrane fouling which results from deposition and nonspecific adsorption of proteins on the membrane surface is irreversible in nature, and results in a significant decrease in the membrane performance. To address this problem, two approaches were explored: 1) control of the surface chemistry tethering alumina membranes with organic components and 2) development of a novel photocatalytic membrane that exhibits hydrophilicity and can be easily regenerated. Both approaches can offer a viable route to the synthesis of attractive membranes, in that 1) the density of protein-resistant organic groups such as PEG is controllable by changing scaffolds or synthesis conditions and 2) the photocatalytic nanocomposite membranes can open the way for a new regeneration method that is environmentally benign.

Developing the synthetic control required for the intentional 3-D arrangement of atoms remains a holy grail in crystal engineering and materials chemistry. The explosive development of metal-organic materials in recent decades has shed light on the above problem. Their properties can be tuned by varying the organic and/or inorganic building units. In addition, their crystallinity makes it possible to determine their structures via the X-ray diffraction method. This dissertation will focus on the chemistry and applications of two kinds of metal-organic materials, namely, metal-organic frameworks (MOFs) and metal-organic polyhedra (MOP). MOFs are coordination polymers. Their permanent porosity makes them a good “gas sponge”. In the first section, an isoreticular series of MOFs with dendritic hexacarboxylate ligands has been synthesized and characterized structurally. One of the MOFs in this series, PCN-68, has a Langmuir surface area as high as 6033 m2 g-1. The MOFs also possess excellent gas (H2, CH4, and CO2) adsorption capacity. In the second section, a NbO-type MOF, PCN-46, was constructed based on a polyyne-coupled di-isophthalate linker formed in situ. Its lasting porosity was confirmed by N2 adsorption isotherm, and its H2, CH4 and CO2 adsorption capacity was examined at 77 K and 298 K over a wide pressure range (0-110 bar). Unlike MOFs, MOP are discrete porous coordination nanocages. In the third section, a MOP covered with bulky triisopropylsilyl group was synthesized, which exhibits a thermosensitive gate opening property. This material demonstrates a molecular sieving effect at a certain temperature range, which could be used for gas separation purpose. In the last section, a MOP covered with alkyne group was synthesized through kinetic control. The postsynthetic modification via click reaction with azide-terminated polyethylene glycol turned them into metallomicelles, which showed controlled release of an anticancer drug 5-fluorouracil. In summary, two kinds of metal-organic materials have been discussed in this dissertation, with the applications in gas storage, gas separation, and drug delivery. These findings greatly enrich the chemistry and applications of metal-organic materials.

Zeolite membranes are attractive materials to separate gas and liquid mixtures. MFI is a widely studied zeolite type due to its ease of preparation and comparable pore size with the molecular size of many substances. In this study MFI type membranes were synthesized over porous &amp / #945 / -Al2O3 supports and characterized with XRD, SEM and gas permeation measurements. In the first part of this study the effect of soda concentration of the synthesis solution on the membrane morphology and crystal orientation was investigated. The synthesis was carried out from solutions with a molar composition of (0- 6.5)Na2O:25SiO2:6.9TPABr:1136H2O at 150oC. At soda concentrations between 0.45 and 1.8 the membrane layers with (h0h)/c-directed orientation were obtained. At lower and higher soda concentrations membrane layer formed from randomly oriented crystals. The (h0h)/c-oriented membranes showed H2/n-C4H10 ideal selectivities of 478 and 36 at 25&deg / C and 150&deg / C, respectively.In the second part, MFI membranes were synthesized from mixtures with different concentrations of template molecules. Tetrapropylammonium hydroxide, tetrapropylammonium bromide or mixture of both types were used as template. The nucleation period, the size of MFI crystals, membrane thickness decreased as the tetrapropylammonium hydroxide concentration increased. Besides conversion of SiO2 in the synthesis solution to MFI passed through a maximum with increasing concentration of tetrapropylammonium hydroxide in the synthesis solution. When tetrapropylammonium bromide was used as template thicker membranes were obtained. In the third part MFI type membranes with a thickness of 1.5-2 &amp / #956 / m were synthesized by mid-synthesis addition of silica to the synthesis medium. The membranes synthesized with and without mid-synthesis addition of silica have n-C4H10/i-C4H10 ideal selectivities of 47 and 8 at 100oC, respectively. The change of composition during the synthesis increases the crystal growth rate and the size of the crystals forming the membrane, thus better quality membranes can be obtained by mid-synthesis addition of silica to the synthesis medium. In the last part of this study, thin MFI type zeolite membranes were synthesized in a recirculating flow system at 95&deg / C on the inner side of the tubular &amp / #945 / - alumina supports. A membrane synthesized by two consecutive synthesis steps had a separation selectivity of 38 and 86 for equimolar mixtures of n- C4H10/CH4 and n-C4H10/N2 at 25oC, respectively. The membrane selectively permeated large n-C4H10 over small CH4 and N2, suggesting that the separation is essentially adsorption-based and the membrane has few nonselective intercrystalline pores.

Membrane based separation techniques have been widely used and developed over decades. Generally polymeric membranes are used in membrane based gas separation / however their gas separation performances are not sufficient enough for industrial feasibility. On the other hand inorganic membranes have good separation performance but they have processing difficulties. As a consequence mixed matrix membranes (MMMs) which comprise of inorganic particles dispersed in organic matrices are developed. Moreover, to enhance the interaction between polymer and zeolite particles ternary mixed matrix membranes are introduced by using low molecular weight additives as third component and promising results were obtained at 35 &deg / C. Better understanding on gas transport mechanism of these membranes could be achieved by studying the effect of preparation and operating parameters. This study investigates the effect of operation temperature and annealing time and temperature on gas separation performance of MMMs. The membranes used in this study consist of glassy polyethersulfone (PES) polymer, SAPO-34 particles and 2- v hidroxy 5-methyl aniline (HMA) as compatibilizer. The membranes fabricated in previous study were used and some membranes were used as synthesized while post annealing (at 120&deg / C, 0.2atm, N2 atm, 7-30 days) applied to some membranes before they are tested. The temperature dependent gas transport properties of the membranes were characterized by single gas permeation measurements of H2, CO2, and CH4 gases between 35 &deg / C-120 &deg / C. The membranes also characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Annealing time and temperature affected the reproducibility and stability of the mixed matrix membranes and by applying post annealing step to mixed matrix membranes at higher temperatures and longer times, more stable membranes were obtained. For pure PES membranes thermally stable performances were obtained without any need of extra treatment. The permeabilities of all studied gases increased with increasing operation temperature. Also the selectivities of H2/CO2 were increased while CO2/CH4, H2/CH4 selectivities were decreased with temperature. The best separation performance belongs to PES/SAPO-34/HMA mixed matrix membrane at each temperature. When the temperature increased from 35 &deg / C to 120 &deg / C H2/CO2 selectivity for PES/SAPO- 34/HMA membrane was increased from 3.2 to 4.6 and H2 permeability increased from 8 Barrer to 26.50 Barrer. This results show that for H2/CO2 separation working at higher temperatures will be more advantageous. The activation energies were found in the order of / CH4 &gt / H2&gt / CO2 for all types of membranes. Activation energies were in the same order of magnitude for all membranes but the PES/SAPO-34 membrane activation energies were slightly lower than PES membrane. Furthermore, PES/SAPO-34/HMA membrane has activation energies higher than PES/SAPO-34 membrane and is very close to pure membrane which shows that HMA acts as a compatibilizer between two phases.

A new group of nanoporous materials, metal organic frameworks (MOFs), have emerged as a fascinating alternative to more traditional nanoporous materials for membrane based gas separations. Although hundreds of different MOF structures have been synthesized in powder forms, very little is currently known about the potential performance of MOFs as membranes since fabrication and testing of membranes from new materials require a large amount of time and resources. The purpose of this thesis is to predict the macroscopic flux of multi-component gas mixtures through MOF-based membranes with information obtained from detailed atomistic simulations. First, atomically detailed simulations of gas adsorption and diffusion in MOFs combined with a continuum description of a membrane are introduced to predict the performance of MOF membranes. These results are compared with the only available experimental data for a MOF membrane. An efficient approximate method based on limited information from molecular simulations to accelerate the modeling of MOF membranes is then introduced. The accuracy and computational efficiency of different modeling approaches are discussed. A robust screening strategy is proposed to screen numerous MOF materials to identify the ones with the high membrane selectivity and to direct experimental efforts to the most promising of many possible MOF materials. This study provides the first predictions of any kind about the potential of MOFs as membranes and demonstrates that using molecular modeling for this purpose can be a useful means of identifying the phenomena that control the performance of MOFs as membranes.

Inorganic-polymer hybrid materials have a high potential to enable major advances in material performance in a wide range of applications. This research focuses on characterizing and tailoring the physics and chemistry of inorganic-polymer interfaces in fabricating high-performance zeolite-polymer mixed-matrix membranes for energy-efficient gas separations. In addition, the topic of novel metal nanoparticle-coated polymer microspheres for optical applications is treated in the Appendix. In zeolite/polymer mixed-matrix membranes, interfacial adhesion and interactions between dope components (zeolite, polymer and solution) play a crucial role in determining interfacial morphology and particle dispersion. The overarching goal is to develop accurate and robust tools for evaluating adhesion and interactions at zeolite-polymer and zeolite-zeolite interfaces in mixed-matrix membrane systems. This knowledge will be used ultimately for selecting proper materials and predicting their performance. This project has two specific goals: (1) development of an AFM methodology for characterizing interfacial interactions and (2) characterization of the mechanical, thermal, and structural properties of zeolite-polymer composites and their correlation to the zeolite-polymer interface and membrane performance. The research successfully developed an AFM methodology to determine interfacial interactions, and these were shown to correlate well with polymer composite properties. The medium effect on interactions between components was studied. We found that the interactions between two hydrophilic silica surfaces in pure liquid (water or NMP) were described qualitatively by the DLVO theory. However, the interactions in NMP-water mixtures were shown to involve non-DLVO forces arising from bridging of NMP macroclusters on the hydrophilic silica surfaces. The mechanism by which nanostructured zeolite surfaces enhanced in zeolite-polymer interfacial adhesion was demonstrated to be reduced entropy penalties for polymer adsorption and increased contact area. ¡¡¡¡¡¡Metal nanoparticle (NP)-coated polymer microspheres have attracted intense interest due to diverse applications in medical imaging and biomolecular sensing. The goal of this project is to develop a facile preparation method of metal-coated polymer beads by controlling metal-polymer interactions. We developed and optimized a novel solvent-controlled, combined swelling-heteroaggregation (CSH) technique. The mechanism governing metal-polymer interaction in the fabrication was determined to be solvent-controlled heteroaggregation and entanglement of NPs with polymer, and the optical properties of the metal/polymer composite beads were shown to make them useful for scattering contrast agent for biomedical imaging and SERS (Surface-Enhanced Raman Scattering) substrates.

Compared to the conventional amine adsorption process to separate CO₂ from natural gas, the membrane separation technology has exhibited advantages in easy operation and lower capital cost. However, the high CO₂ partial pressure in natural gas can plasticize the membranes, which can lead to the loss of CH₄ and low CO₂/CH₄ separation efficiency. Crosslinking of polymer membranes have been proven effective to increase the CO₂ induced plasticization resistance by controlling the degree of swelling and segmental chain mobility in the polymer. This thesis focuses on extending the success of crosslinking to more productive asymmetric hollow fibers. In this work, the productivity of asymmetric hollow fibers was optimized by reducing the effective selective skin layer thickness. Thermal crosslinking and catalyst assisted crosslinking were performed on the defect-free thin skin hollow fibers to stabilize the fibers against plasticization. The natural gas separation performance of hollow fibers was evaluated by feeding CO₂/CH₄ gas mixture with high CO₂ content and pressure.

Thesis (Ph. D.)--Ohio State University, 2009. / Title from first page of PDF file. Includes bibliographical references (p. 268-291).

The gas transport properties of side-chain crystalline poly(n-alkyl acrylate) and poly(m-alkyl acrylate) blends are determined as a function of temperature for varying side-chain lengths, n and m, and blend compositions. The side chains of poly(n-alkyl acrylate)s crystallize independently of the main chain for n [is greater than or equal to] 10 which leads to an extraordinary increase in the permeability at the melting temperature of the crystallites. The compatibility of these polymers are examined and macroscopic homogeneity is observed for a small range of n and m when the difference /n - m/ is between 2 - 4 methylene units. Thermal analysis shows that the blend components crystallize independently of one another; at the same time, the crystallization of each component is hindered by the presence the other component. The permeation responses of these blends show two distinct permeation jumps as the crystallites from each component melt at their respective melting temperatures. Blends with continuous permeation responses are found to have higher effective activation energies than observed for common polymers. Thermal analysis proved to be a useful tool to help predict the permeation response for poly(alkyl acrylates); thus the thermal behavior of poly(n-alkyl acrylate) blended with n-aliphatic materials and random copolymers of poly(n-alkyl acrylates) are briefly examined. A bulk modified atmospheric storage design is proposed where produce is stored in a rigid chamber that is equipped with both selective and non-selective membrane modules that help regulate the oxygen entering and the carbon dioxide leaving the produce compartment. The design enables control of the atmosphere inside the chamber by modulating gas flow, i.e. the gas flow rate and composition, through the non-selective membrane by delivering fresh air upstream of the non-selective membrane. The model shows that the choice of materials for the selective and non-selective membranes dictate the range of concentrations achievable; however, the air flow rate allows the control between these ranges. The method to design a practical chamber from this model is also described.

The removal of higher hydrocarbons from natural gas streams is an important separation that has been identified as a growth area for polymer membranes. An ideal membrane material for this separation would be more permeable to higher hydrocarbons (i.e., C3+ compounds) than to CH₄. This allows the CH₄ rich permeate to be retained at or near feed pressure, thus minimizing the requirement for repressurization followingmembrane separation. A polymer which demonstrates the ability to separate vapor from gases with high efficiency is poly [1-(trimethylsilyl)-1-propyne] (PTMSP). PTMSP is a stiff chain, high free volume glassy polymer well known for its very high gas permeability and outstanding vapor/gas selectivity. However, PTMSP is soluble in many organic compounds, leading to potential dissolution of the membrane in process streams where its separation properties are of greatest interest. PTMSP also undergoes significant physical aging, which is the gradual relaxation of non-equilibrium excess free volume in glassy polymers. Crosslinking PTMSP with bis(azide)s was undertaken in an attempt to increase the solvent resistance and physical stability of the polymer. A fundamental investigation into crosslinking PTMSP with a bis(azide) crosslinker was the focus of this thesis. Pure gas transport measurements were conducted with N₂, O₂, CH₄, C₂H6, C₃H₈, and n-C₄H₁₀ over temperatures raging from -20°C to 35°C and pressures ranging from 0 to 20 atm. Mixed gas permeation experiments were conducted using a 98 mol % CH₄, and 2 mol % n-C₄H₁₀ mixture. The mixed gas permeation experiments were conducted at temperatures ranging from -20°C to 35°C, and pressures ranging from 4 to 18 atm. Inorganic nanoparticles such as fumed silica (FS) were added to uncrosslinked and crosslinked PTMSP, and the effects of their addition on the transport properties were investigated. Crosslinking PTMSP with bis(azide)s increases its solvent resistance, and crosslinked films are insoluble in common PTMSP solvents such as toluene. At all temperatures, the initial pure and mixed gas permeabilities of crosslinked PTMSP films are less than those of uncrosslinked PTMSP. This decrease in permeability is consistent with the fractional free volume (FFV) decrease that accompanies crosslinking. Pure gas solubility coefficients are relatively unaffected by the crosslinking process, so the decrease in permeability is caused by decreases in diffusivity. The addition of FS nanoparticles increases the initial pure and mixed gas permeabilities of uncrosslinked and crosslinked PTMSP. The pure gas permeabilities and solubilities of all PTMSP films increase when the temperature decreases, while the diffusivities decrease. The rates of change in pure gas transport properties with temperature is similar for all films, so the temperature dependence of pure gas transport properties of PTMSP is unaffected by the addition of crosslinks or FS. The aging of uncrosslinked and crosslinked PTMSP films was investigated by monitoring N₂, O₂ and CH₄ permeabilities and FFV over time. The FFV and permeabilities of crosslinked films decreased over time, so crosslinking did not arrest the physical aging of PTMSP, as has been previously reported, and these differences in aging observations are likely to be a consequence of differences in post film casting thermaltreatments. The addition of 10 wt % polysiloxysilsesquioxanes (POSS) nanoparticles decreases the permeabilities of uncrosslinked and crosslinked PTMSP by approximately 70 %, and the permeability and FFV values of the resulting nanocomposite films were stable over the course of 200 days. In all PTMSP films, the mixed gas permeabilities of n-C₄H₁₀ increase with decreasing temperature, while the mixed gas CH₄ permeabilities decrease with decreasing temperature. As a result, the mixed gas n-C₄H₁₀/CH₄ permeability selectivities increase with decreasing temperatures. The addition of crosslinks and FS nanoparticles to PTMSP decreases the mixed gas n-C₄H₁₀/CH₄ permeability selectivities, and changes in the free volume characteristics of PTMSP caused by crosslinking and FS nanoparticles are thought to reduce the blocking of CH₄ permeation by n-C₄H₁₀. / text