UNDERSTANDING THE PROPERTY-PERFORMANCE RELATIONSHIPS OF MEMBRANE ACTIVE LAYERS CONTAINING POROUS NANOPARTICLES

Thin-film nanocomposite (TFN) membranes for water purification have emerged in the last decade as a class of membranes that can provide increased water productivity over traditional thin-film composite (TFC) membranes, but still maintain the same level of contaminant rejection. The mechanisms by which the increased water permeability is achieved are not well understood as there are no comprehensive studies on the relevant structure-performance relationships. Accordingly, the overall objective of this study was to advance the understanding of the property-performance relationships of TFN membranes containing porous nanoparticles in their active layers. Towards achieving my overall objective, I pursued the following specific objectives: (i) to develop a method to measure charge density in active layers of polyamide-based TFC and TFN membranes; (ii) to characterize the effect of LTA zeolite loading on the physico-chemical properties of the active layers of zeolite TFN membranes, and investigate their corresponding structure-performance relationships; and (iii) to characterize the effect of ZIF8 nanoparticle loading, surface area, and size on the performance of ZIF8-TFN membranes, and investigate their corresponding structure-performance relationships. Overall, the results obtained in this study showed that zeolite and ZIF8 nanoparticle incorporation into active layers results in higher water productivity, and unchanged salt rejection up to a zeolite loading threshold above which salt rejection decreases (~0.15 wt% in the organic TMC solution used to cast the active layer). Results and analyses also showed that the observed changes in the physico-chemical properties of the active layer polymer did not explain the observed changes in membrane performance. Therefore, it is concluded that the increased water productivity of TFN membranes over the control TFC membranes is the result of water transport through the porous structure of LTA zeolite and ZIF8 nanoparticles, or along the polymer-nanoparticle interface. Alternatively, nanoparticle incorporation may have changed properties of the active layer polymer not characterized in this study (i.e., water diffusivity, or microstructure) in such a way such that it led to greater water permeability.Doctor of Philosoph

Applications of aluminosilicate and zincosilicate materials: aqueous phase ion exchange and gas phase adsorption

Doctor of PhilosophyDepartment of Chemical EngineeringJennifer L. AnthonyZeolites and zeolite-like materials have well-ordered structures and pores creating varying capacities for molecules based upon size, functional groups, polarity, and intermolecular forces making the materials useful for molecular sensing as well for molecules that are considered hazardous at very low concentrations with reproducible results because of these properties. This study will identify and characterize applications for zeolite and zeolite-like materials in gas and liquid phases based upon the dominating physical and chemical properties of the materials. The properties of interest include liquid phase ion exchange capacities, selectivities, gas/vapor phase adsorption capacity, and initial adsorption uptake rate. Zincosilicates have similar framework structures to aluminosilicate zeolites; however, they have distinct advantages over traditional zeolites. Zincosilicates typically have a higher ion density, lack “cages” in their structure which leads to all the cations being accessible for ion exchange, and have the ability to form three-membered rings which lead to large void spaces in their structure. These features lead to high capture capacities for divalent heavy metal mercury ions. In this work, the potential to use zincosilicates as ion exchangers such as VPI-7, VPI-9 and VPI-10 is presented. Results have shown that zincosilicates have capture capacities greater than traditional zeolites, even greater than those that have been synthesized with functional groups intended to increase metal sorption capacities. The selectivity coefficients in a binary ion exchange system were successfully modeled using the Gibbs-Donnan selectivity model. The selectivities for the zincosilicates were Pb>Na>Hg>K>Ca. Zeolites are also able to adsorb chemical species and therefore can be used as the recognition element in sensing devices. The sorption capacity of 2-chloroethyl ethyl sulfide, dimethyl methanephosphonate, ethanol, and n-butanethiol were examined with zeolites 13X, 4A, MCM-41, VPI-7, VPI-9, and ZSM-5. The zeolites selected provided very different framework composition, countercation, and surface area features for determining the most significant properties in adsorption. Zeolite 13X had the highest equilibrium and initial uptake rate for most compounds tested, whereas the low surface area zincosilicates, VPI-7 and VPI-9, had the lowest capacity. Based on these results, a piezoelectric device with an array of zeolites can be successfully employed as a sensor

Cryodeposit Thin Film Detection Techniques in a High-Vacuum Environment

It has been well documented that the principal source of contamination for optics in cryogenic systems is water. Prior studies have been successfully performed to explore methods to detect and accurately measure ice growth on optical surfaces. A new setup to detect cryodeposit thin films in high vacuum environments is under development and has been tested at the University of Tennessee Space Institute’s (UTSI) Center for Laser Applications (CLA). This setup uses a multiple-beam laser interferometer that is incident the mirror surface at 45 degrees to the normal surface. Water vapor was introduced to the vacuum system via 3-angstrom zeolite molecular sieves, thus allowing ice growth to take place on both a quartz-crystal microbalance (QCM) and a gold-plated first surface mirror. Three experimental runs involving ice-accumulation on the mirror and QCM were performed. Each experimental run lasted for a minimum of two hours in order to allow a significant amount of ice to form on the test surfaces. Using data from both the QCM and multi-beam interferometer, we were able to effectively and non-invasively measure the accumulated cryogenic ice layer thickness. During the final two-hour and thirty-two-minute run on November 26th, 2013, we obtained ice thickness values of 3.25 micrometers and 2.88 micrometers with the interferometer and QCM, respectively. The thickness values measured by the QCM and interferometer were within 12.2% of each other

Formation of Biomimetic Membranes on Inorganic Supports of Different Surface Morphology and Macroscopic Geometry

abstract: Biological membranes are critical to cell sustainability by selectively permeating polar molecules into the intracellular space and providing protection to the interior organelles. Biomimetic membranes (model cell membranes) are often used to fundamentally study the lipid bilayer backbone structure of the biological membrane. Lipid bilayer membranes are often supported using inorganic materials in an effort to improve membrane stability and for application to novel biosensing platforms. Published literature has shown that a variety of dense inorganic materials with various surface properties have been investigated for the study of biomimetic membranes. However, literature does not adequately address the effect of porous materials or supports with varying macroscopic geometries on lipid bilayer membrane behavior. The objective of this dissertation is to present a fundamental study on the synthesis of lipid bilayer membranes supported by novel inorganic supports in an effort to expand the number of available supports for biosensing technology. There are two fundamental areas covered including: (1) synthesis of lipid bilayer membranes on porous inorganic materials and (2) synthesis and characterization of cylindrically supported lipid bilayer membranes. The lipid bilayer membrane formation behavior on various porous supports was studied via direct mass adsorption using a quartz crystal microbalance. Experimental results demonstrate significantly different membrane formation behaviors on the porous inorganic supports. A lipid bilayer membrane structure was formed only on SiO2 based surfaces (dense SiO2 and silicalite, basic conditions) and gamma-alumina (acidic conditions). Vesicle monolayer adsorption was observed on gamma-alumina (basic conditions), and yttria stabilized zirconia (YSZ) of varying roughness. Parameters such as buffer pH, surface chemistry and surface roughness were found to have a significant impact on the vesicle adsorption kinetics. Experimental and modeling work was conducted to study formation and characterization of cylindrically supported lipid bilayer membranes. A novel sensing technique (long-period fiber grating refractometry) was utilized to measure the formation mechanism of lipid bilayer membranes on an optical fiber. It was found that the membrane formation kinetics on the fiber was similar to its planar SiO2 counterpart. Fluorescence measurements verified membrane transport behavior and found that characterization artifacts affected the measured transport behavior.Dissertation/ThesisPh.D. Chemical Engineering 201

Colloidal Porous Nanoparticles

Colloidal porous hosts in the form of microporous aluminosilicate (zeolite) or mesoporous silica nanoparticles are attractive materials for a wide range of potential applications, i.e. controlled release drug delivery systems. However, many fundamental challenges still remain in this relatively young research field. The following work focuses on overcoming some of the present limitations by developing new concepts for the synthesis and functionalization of porous nanoparticles. The number of zeolite structures available for the synthesis of stable colloidal suspensions is very limited when compared to the large number of known frameworks in bulk materials. A novel class of zeolite templates in the form of metal ammines was developed by taking advantage of the unique synthesis conditions typical in colloidal zeolite systems, i.e. low temperatures and low alkalinity. Square planar copper(II) tetraammine complexes were employed as co-templates in the synthesis of nanosized EDI-type molecular sieves. It was shown that the complexes are the key elements responsible for formation and growth of the zeolite nanoparticles, and their role in the crystallization process was thoroughly investigated. Substitution of the copper complexes by isostructural palladium and platinum species was demonstrated. By employing templates with similar shapes but different effects on the nucleation rate it was possible to drastically decrease the particle size by several factors in comparison to previously known colloidal zeolite systems and to generate stable suspensions of non-agglomerated EDI-type nanocrystals with diameters below 20 nm. The size and morphology of mesoporous silica nanoparticles was controlled by co-condensation with additives, i.e. phenyltriethoxysilane, and subsequent simultaneous removal of the functional groups and template molecules by oxidation with hydrogen peroxide in a simple one-pot reaction. Conversion of colloidal mesoporous silica systems with metalorganic reagents was demonstrated. The key step for avoiding particle agglomeration and coalescence processes involves the removal of water from the mesopores at temperatures below 90 °C either by hydrolysis of triethyl orthoformate or by vapour adsorption from the gas phase. In a joint project with Alexander Darga from our group, thin films of different phenyl-substituted mesoporous silica nanoparticles were deposited on quartz crystal microbalance chips in order to probe the intrapore surfaces by toluene sorption. It was shown that samples prepared by grafting and co-condensation approaches bearing similar surface densities of functional groups display considerably different toluene heats of adsorption. Furthermore, a novel concept for the selective functionalization of mesoporous silica nanoparticles was developed. By using a time-delayed co-condensation approach, functional groups can be completely dispersed inside the channels, concentrated in parts of the mesopores, or exclusively placed on the external surface depending on the time of addition. Aminopropyl was used as a representative functionality in order to determine the density of functional groups on the outer surface via zeta potential measurements. Staining with iridium cations and subsequent scanning transmission electron microscopy studies allowed the visualization of metal clusters with different radial distributions depending on the addition time of the organosilane component. In contrast to grafting approaches, it was possible to easily adjust the concentration of functional groups on the outer surface by variation of the organosilane to silane ratio

Towards Engineering Advanced Nanomaterials: Elucidating Fundamental Particle Behavior in Water and Critical Sorption Dynamics

As advanced nanomaterials, inorganic-organic nano composites have received great interest as potential platform (nano) structures for sensor, catalyst, sorbent, and environmental applications. Here, my Ph.D. research has focused on the design, synthesis, and characterization of advanced water-stable engineered metal-oxide nanoparticles functionalized by organic frames for environmental applications. For the environmental applications, I have evaluated particleoptimized sorption processes for the remediation and separation of arsenic, chromium, and uranium under environmentally relevant conditions. More specifically, I have explored the critical role of organic coating on sorption mechanisms and performances using engineered iron oxide -based, manganese oxide -based, and manganese ferrite -based (core) nanoparticles with varying size, composition, surface coating and functional groups. With the application for environmental remediation of organic functionalized metal oxide nanoparticles, implication of advanced materials is another essential subject for environmental nano impact. As environmental implications, I fundamentally described material transport behavior(s), including aggregation and deposition in terms of surface organic matrix; I quantitatively explored the role of organic coating on collision and attachment of inorganic-organic nano composites for the environmental fate and transport of new nano platforms. Further, I evaluated highly stable organic coated superparamagnetic nanoparticles as potential draw solute for osmotic pressure driven membrane system to exploit paramagnetism of the particles. These works suggest better understanding of environmental application and implication for inorganic-organic nano composites

Thin Films from Porous Nanoparticles

Porous materials in the nanometer range are interesting materials in many fields of science and technology. Especially in terms of colloidal suspensions, these materials are promising candidates for applications such as gas sensing, host-guest chemistry, drug delivery and coatings in the semiconductor industry. In this work, syntheses of monodisperse, stable, colloidal suspensions of different materials for the preparation of porous thin films were described. Colloidal suspensions of zeolite Beta nanocrystals with low aluminum content were prepared and the crystallization kinetics was studied. The crystalline Beta was stabilized in colloidal suspensions by addition of inorganic silica-based binders and applied for the preparation of films by a spin-on process. The thickness of the films was controlled by repeated coating steps, speed of deposition and Beta concentration of the coating suspensions. The Beta films exhibit good mechanical properties, smooth surfaces and show a low refractive index, which is typical for highly porous silica based materials. Additionally, a synthetic approach for the preparation of colloidal mesoporous silica spheres and functionalized colloidal suspensions of nanoscale mesoporous materials with high yields from concentrated solutions is presented. Narrow particle size distributions in the range of about 50 to 150 nm were established with Dynamic Light Scattering measurements and electron microscopy before and after template extraction. Discrete nanoscale mesoporous particles with functionalized pore surfaces resulted when adding functional organoalkoxysilanes directly to the initial silica precursor solutions. Nitrogen sorption analysis indicated that the functional groups were located at the inner surfaces of the mesoporous channel systems. By further decreasing the diameter of these mesoporous silica spheres, their scattering ability for visible light was also drastically decreased. We have demonstrated the synthesis of extremely small mesoporous silica nanoparticles via a specific co-condensation process with phenyl groups. If the size of the particles falls below about 1/10 of the wavelength of the incoming light (0.1 ), the colloidal suspensions show optical transparency. Because of an easy handling and a good reproducibility, the suspensions are ideal for the production of thin film by spin-coating. The films showed excellent optical qualities, exhibited good diffusion properties and a highly accessible pore system. Thanks to the small particle size and the resulting low surface roughness, the formation of multilayers was possible without transmitting defects on the surface with every following coating step. The availability of such homogeneous porous thin films made it possible to use ellipsometry as analysis method. Ellipsometric porosimetry (EP) is a convenient method to determine the effective porosity of a thin film on its original support without destroying it. It was possible to record sorption isotherms of the thin films with ellipsometry and to correlate the data with nitrogen sorption data of dried powders of the same material. The thin films showed very low refractive indices around 1.2 in the case of both, zeolites and functionalized mesoporous silica nanoparticles. Besides, a synthesis procedure for TiO2 particles in an acidic medium by a simple sol-gel process was investigated. The material showed a high surface area and the thin films prepared from the colloidal suspensions had a high refractive index combined with a certain porosity. Thus, the preparation of wavelength specific Bragg mirrors could be realized by a simple and reproducible spin-coating approach using colloidal suspensions of functionalized porous silica nanoparticles and titania sols. The Bragg reflectors show a sensitivity towards specific relative pressures of organic vapors like isopropanol or toluene

Applications of electrospun nanofibers in filtration processe

Thesis (Doctoral)--İzmir Institute of Technology, Chemistry, İzmir, 2013Includes bibliographical references (leaves: 136-161)Text in English; Abstract: Turkish and Englishxxi, 161 leavesElectrospinning is a simple and versatile method to fabricate ultrathin fibrous mats from a wide variety of organic and/or inorganic materials. Since it allows fabricating fiber diameter and surface/internal structures by solution and instrumental parameters, electrospun fibers provide much enhanced functionalities, which can not be obtained by bulk materials. This thesis examines the filtration, sensing and catalytical applications associated with the remarkable features of electrospun nanofibers. The systems studied are reported herein; (i) The first part of this dissertation deals with the filtration applications of electrospun nanofibrous membranes. Nano-sized chitosan fibers were utilized for sorption of Fe(III), Cu(II), Ag(I), and Cd(II) ions from aqueous solutions. The surface of chitosan fibers were further functionalized by monodisperse nano zero-valent iron (nZVI) particles for the removal of inorganic arsenic species. Sorption of radioactive U(VI) ions from aqueous systems via column sorption under continuous flow was performed using amidoximated polyacrylonitrile fibers. (ii) The second part of this dissertation presents sensing applications of ceramic fibers. Humidity sensing properties of electrospun ZnO fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. Electrospinning technique was used as coating process for deposition of CeO2/ZnO and ZnO based nanofibers on the electrode of QCM. The fiber-coated QCM sensors were used for the detection of volatile organic compounds (VOCs). (iii) The last part of this dissertation describes an approach to fabricate hierarchically structured composite nanofibers. The nanostructured materials prepared by the simultaneous electrospinning of CeO2 and LiCoO2 precursors and SiO2 nanoparticles were used for the photocatalytic degradation of Rhodamine B

Towards Multiplexed Electrogenerated Chemiluminescent Detection

The main objective of this dissertation is to understand and study the principle of electrogenerated chemiluminescence (ECL) and its applications to detect biomolecules simultaneously. Four aspects of ECL were studied. In order to carry out multiplexed ECL detection, both classical and several novel ECL systems have been investigated. In the first aspect, significant effect of chloride ions on the ECL behavior of the tris(2,2′-bipyridyl) ruthenium(II) (Ru(bpy)3 2+)/tri-n-propylamine (TPrA) system at Au electrode was investigated. At low concentrations (e.g., [Cl-] \u3c 5 mM), the ECL was enhanced; at relatively high concentrations, however, the ECL intensity decreased with the increase of the [Cl-]. At [Cl-] = 90 mM, ~ 50% and 100% ECL inhibition was observed for the first and the second ECL wave, respectively. The electrogenerated chloroaurate anions (AuCl2 - and AuCl4 -) which were verified using an electrochemical quartz-crystal microbalance (EQCM) method were found to be responsible for the ECL inhibition. This study suggests that care must be taken when Au working electrode is used for ECL studies in chloride-containing buffer solutions (widely used in DNA probes) and/or with the commonly used chloride-containing reference electrodes since in these cases the ECL behavior may significantly disagree with that obtained using other electrodes and reaction media. In the second aspect, the electrochemical behavior of a trinuclear ruthenium(II)- containing complex, [((phen)2Ru(dpp))2RhCl2]5+ (where phen = 1,10-phenanthroline, dpp = 2,3-bis-2-pyridylpyrazine), was studied in acetonitrile (MeCN) and aqueous solutions. In MeCN containing 0.10 M tetra-n-butylammonium perchlorate (TBAP), the complex displayed a reversible, overlapping RuII/III redox process with E1/2 = +1.21 V vs Ag/Ag+ (10 mM), an irreversible reduction of RhIII/I at -0.73 V vs Ag/Ag+, and two quasireversible dpp/dpp- couples with E1/2 = -1.11 V and -1.36 V vs Ag/Ag+ at a Pt electrode with a scan rate of 50 mV s-1. In 0.20 M Tris buffer solution (pH 7.4), an irreversible, overlapping RuII/III oxidation at +1.48 V vs Ag/AgCl (3 M KCl), and an irreversible reduction of RhIII/II at -0.78 V vs Ag/AgCl were observed at a glassy carbon electrode with a scan rate of 50 mV/s. Investigations on the ECL of the complex revealed that 2-(dibutylamino) ethanol (DBAE) was superior to TPrA as an ECL coreactant within their entire concentration range of 10-100 mM in MeCN, and in aqueous media, as low as 1.0 nM of the complex could be detected using TPrA coreactant ECL. A maximum ECL emission of 640 nm, which is about 55 nm blue-shifted with respect to its fluorescence peak, was observed in MeCN with DBAE as a coreactant. Interactions of the complex with calf thymus DNA (ctDNA) were conducted with a flow-cell based QCM, and a binding constant of 2.5×105 M-1 was calculated on the basis of the Langmuir isotherm equation. In the third aspect, ECL behavior of core/shell semiconductor CdSe/ZnS nanocrystals coated with a carboxyl polymer layer (quantum dot, Qdot, or QDs) was studied in aqueous solutions using TPrA and DBAE as ECL coreactant. Upon the anodic potential scanning, strong ECL emissions were observed at glassy carbon (GC) electrode within the potential range of ~0.75 to 1.5 V vs Ag/AgCl (3.0 M KCl) when DBAE was used as the coreactant. The ECL behavior of the Qdot was found to be strongly dependent on the types and concentrations of ECL coreactants as well as the nature of the working electrode. The ECL emission measured with the Qdot/DBAE/GC electrode system has a peak value of ~625 nm, which matched well with its fluorescence. The Qdot as a label for ECL-based C-reactive protein (CRP) immunoassays was realized by covalent binding of avidin on its surface, which allowed biotinalyted antibodies to be attached and interacted with antigens and the antibodies linked to micro-sized magnetic beads. The newly formed sandwich type aggregates were separated magnetically from the solution matrix, followed by the ECL generation in the presence of the coreactant DBAE. ECL experiments were carried out with a potential scan from 0 to 1.5 V vs Ag/AgCl at partially transparent Au/CD electrodes, and the integrated ECL intensity was found to be linearly proportional to the CRP concentration over the range of 1.0-10.0 μg/mL. In the fourth aspect, the ECL behavior of Ru(bpy)3 2+, 9,10-diphenylanthracene DPA), and rubrene (RUB) with DBAE or TPrA as the coreactant was studied in acetonitrile solution. The ECL emission spectra of the mixed solution including the above three ECL labels were investigated. The ECL maximum emissions at ~440 nm for DPA, ~560 nm for RUB, and ~630 nm for Ru(bpy)3 2+ were linearly proportional to the concentration of each individual ECL labels in mixed solutions, suggesting that multiplexing detection and quantification of biomolecules with ECL technology is feasible