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Description
Topological insulators with conducting surface states yet insulating bulk states have generated a lot of interest amongst the physics community due to their varied characteristics and possible applications. Doped topological insulators have presented newer physical states of matter where topological order co&ndashexists; with other physical properties (like magnetic order). The electronic states of these materials are very intriguing and pose problems and the possible solutions to understanding their unique behaviors. In this work, we use Electron Energy Loss Spectroscopy (EELS) – an analytical TEM tool to study both core&ndashlevel; and valence&ndashlevel; excitations in Bi2Se3 and Cu(doped)Bi2Se3 topological insulators. We use this technique to retrieve information on the valence, bonding nature, co-ordination and lattice site occupancy of the undoped and the doped systems. Using the reference materials Cu(I)Se and Cu(II)Se we try to compare and understand the nature of doping that copper assumes in the lattice. And lastly we utilize the state of the art monochromated Nion UltraSTEM 100 to study electronic/vibrational excitations at a record energy resolution from sub-nm regions in the sample.
ContributorsSubramanian, Ganesh (Author) / Spence, John (Thesis advisor) / Jiang, Nan (Committee member) / Chen, Tingyong (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
Dealloying, the selective dissolution of an elemental component from an alloy, is an important corrosion mechanism and a technological significant means to fabricate nanoporous structures for a variety of applications. In noble metal alloys, dealloying proceeds above a composition dependent critical potential, and bi-continuous structure evolves "simultaneously" as a result of the interplay between percolation dissolution and surface diffusion. In contrast, dealloying in alloys that show considerable solid-state mass transport at ambient temperature is largely unexplored despite its relevance to nanoparticle catalysts and Li-ion anodes. In my dissertation, I discuss the behaviors of two alloy systems in order to elucidate the role of bulk lattice diffusion in dealloying. First, Mg-Cd alloys are chosen to show that when the dealloying is controlled by bulk diffusion, a new type of porosity - negative void dendrites will form, and the process mirrors electrodeposition. Then, Li-Sn alloys are studied with respect to the composition, particle size and dealloying rate effects on the morphology evolution. Under the right condition, dealloying of Li-Sn supported by percolation dissolution results in the same bi-continuous structure as nanoporous noble metals; whereas lattice diffusion through the otherwise "passivated" surface allows for dealloying with no porosity evolution. The interactions between bulk diffusion, surface diffusion and dissolution are revealed by chronopotentiometry and linear sweep voltammetry technics. The better understanding of dealloying from these experiments enables me to construct a brief review summarizing the electrochemistry and morphology aspects of dealloying as well as offering interpretations to new observations such as critical size effect and encased voids in nanoporous gold. At the end of the dissertation, I will describe a preliminary attempt to generalize the morphology evolution "rules of dealloying" to all solid-to-solid interfacial controlled phase transition process, demonstrating that bi-continuous morphologies can evolve regardless of the nature of parent phase.
ContributorsChen, Qing (Author) / Sieradzki, Karl (Thesis advisor) / Friesen, Cody (Committee member) / Buttry, Daniel (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2013
Description
Cyanovirin-N (CVN) is a cyanobacterial lectin with potent anti-HIV activity, mediated by binding to the N-linked oligosaccharide moiety of the envelope protein gp120. CVN offers a scaffold to develop multivalent carbohydrate-binding proteins with tunable specificities and affinities. I present here biophysical calculations completed on a monomeric-stabilized mutant of cyanovirin-N, P51G-m4-CVN, in which domain A binding activity is abolished by four mutations; with comparisons made to CVNmutDB, in which domain B binding activity is abolished. Using Monte Carlo calculations and docking simulations, mutations in CVNmutDB were considered singularly, and the mutations E41A/G and T57A were found to impact the affinity towards dimannose the greatest. 15N-labeled proteins were titrated with Manα(1-2)Manα, while following chemical shift perturbations in NMR spectra. The mutants, E41A/G and T57A, had a larger Kd than P51G-m4-CVN, matching the trends predicted by the calculations. We also observed that the N42A mutation affects the local fold of the binding pocket, thus removing all binding to dimannose. Characterization of the mutant N53S showed similar binding affinity to P51G-m4-CVN. Using biophysical calculations allows us to study future iterations of models to explore affinities and specificities. In order to further elucidate the role of multivalency, I report here a designed covalent dimer of CVN, Nested cyanovirin-N (Nested CVN), which has four binding sites. Nested CVN was found to have comparable binding affinity to gp120 and antiviral activity to wt CVN. These results demonstrate the ability to create a multivalent, covalent dimer that has comparable results to that of wt CVN.
WW domains are small modules consisting of 32-40 amino acids that recognize proline-rich peptides and are found in many signaling pathways. We use WW domain sequences to explore protein folding by simulations using Zipping and Assembly Method. We identified five crucial contacts that enabled us to predict the folding of WW domain sequences based on those contacts. We then designed a folded WW domain peptide from an unfolded WW domain sequence by introducing native contacts at those critical positions.
WW domains are small modules consisting of 32-40 amino acids that recognize proline-rich peptides and are found in many signaling pathways. We use WW domain sequences to explore protein folding by simulations using Zipping and Assembly Method. We identified five crucial contacts that enabled us to predict the folding of WW domain sequences based on those contacts. We then designed a folded WW domain peptide from an unfolded WW domain sequence by introducing native contacts at those critical positions.
ContributorsWoodrum, Brian William (Author) / Ghirlanda, Giovanna (Thesis advisor) / Redding, Kevin (Committee member) / Wang, Xu (Committee member) / Arizona State University (Publisher)
Created2014
Description
Spider dragline silk is an outstanding biopolymer with a strength that exceeds steel by weight and a toughness greater than high-performance fibers like Kevlar. For this reason, structural and dynamic studies on the spider silk are of great importance for developing future biomaterials. The spider dragline silk comprises two silk proteins, Major ampullate Spidroin 1 and 2 (MaSp1 and 2), which are synthesized and stored in the major ampullate (MA) gland of spiders. The initial state of the silk proteins within Black Widow MA glands was probed with solution-state NMR spectroscopy. The conformation dependent chemical shifts information indicates that the silk proteins are unstructured and in random coil conformation. 15N relaxation parameters, T1, T2 and 15N-{1H} steady-state NOE were measured to probe the backbone dynamics for MA silk proteins. These measurements indicate fast sub-nanosecond timescale backbone dynamics for the repetitive core of spider MA proteins indicating that the silk proteins are unfolded, highly flexible random coils in the MA gland. The translational diffusion coefficients of the spider silk proteins within the MA gland were measured using 1H diffusion NMR at 1H sites from different amino acids. A phenomenon was observed where the measured diffusion coefficients decrease with an increase in the diffusion delay used. The mean displacement along the external magnetic field was found to be 0.35 μm and independent of the diffusion delay. The results indicate that the diffusion of silk protein was restricted due to intermolecular cross-linking with only segmental diffusion observable.
To understand how a spider converts the unfolded protein spinning dope into a highly structured and oriented in the super fiber,the effect of acidification on spider silk assembly was investigated on native spidroins from the major ampullate (MA) gland fluid excised from Latrodectus hesperus (Black Widow) spiders. The in vitro spider silk assembly kinetics were monitored as a function of pH with a 13C solid-state Magic Angle Spinning (MAS) NMR approach. The results confirm the importance of acidic pH in the spider silk self-assembly process with observation of a sigmoidal nucleation-elongation kinetic profile. The rates of nucleation and elongation and the percentage of β-sheet structure in the grown fibers depend on pH.
The secondary structure of the major ampullate silk from Peucetia viridians (Green Lynx) spiders was characterized by X-ray diffraction (XRD) and solid-state NMR spectroscopy. From XRD measurement, β-sheet nano-crystallites were observed that are highly oriented along the fiber axis with an orientational order of 0.980. Compare to the crystalline region, the amorphous region was found to be partially oriented with an orientational order of 0.887. Further, two dimensional 13C-13C through-space and through-bond solid-state NMR experiments provide structural analysis for the repetitive amino acid motifs in the silk proteins. The nano-crystallites are mainly alanine-rich β-sheet structures. The total percentage of crystalline region is determined to be 40.0±1.2 %. 18±1 % of alanine, 60±2 % glycine and 54±2 % serine are determined to be incorporated into helical conformations while 82±1 % of alanine, 40±3 % glycine and 46±2 % serine are in the β-sheet conformation.
To understand how a spider converts the unfolded protein spinning dope into a highly structured and oriented in the super fiber,the effect of acidification on spider silk assembly was investigated on native spidroins from the major ampullate (MA) gland fluid excised from Latrodectus hesperus (Black Widow) spiders. The in vitro spider silk assembly kinetics were monitored as a function of pH with a 13C solid-state Magic Angle Spinning (MAS) NMR approach. The results confirm the importance of acidic pH in the spider silk self-assembly process with observation of a sigmoidal nucleation-elongation kinetic profile. The rates of nucleation and elongation and the percentage of β-sheet structure in the grown fibers depend on pH.
The secondary structure of the major ampullate silk from Peucetia viridians (Green Lynx) spiders was characterized by X-ray diffraction (XRD) and solid-state NMR spectroscopy. From XRD measurement, β-sheet nano-crystallites were observed that are highly oriented along the fiber axis with an orientational order of 0.980. Compare to the crystalline region, the amorphous region was found to be partially oriented with an orientational order of 0.887. Further, two dimensional 13C-13C through-space and through-bond solid-state NMR experiments provide structural analysis for the repetitive amino acid motifs in the silk proteins. The nano-crystallites are mainly alanine-rich β-sheet structures. The total percentage of crystalline region is determined to be 40.0±1.2 %. 18±1 % of alanine, 60±2 % glycine and 54±2 % serine are determined to be incorporated into helical conformations while 82±1 % of alanine, 40±3 % glycine and 46±2 % serine are in the β-sheet conformation.
ContributorsXu, Dian (Author) / Yarger, Jeffery L (Thesis advisor) / Holland, Gregory P (Thesis advisor) / Wang, Xu (Committee member) / Liu, Yan (Committee member) / Arizona State University (Publisher)
Created2015
Description
An animal's ability to produce protein-based silk materials has evolved independently in many different arthropod lineages, satisfying various ecological necessities. However, regardless of their wide range of uses and their potential industrial and biomedical applications, advanced knowledge on the molecular structure of silk biopolymers is largely limited to those produced by spiders (order Araneae) and silkworms (order Lepidoptera). This thesis provides an in-depth molecular-level characterization of silk fibers produced by two vastly different insects: the caddisfly larvae (order Trichoptera) and the webspinner (order Embioptera).
The molecular structure of caddisfly larval silk from the species Hesperophylax consimilis was characterized using solid-state nuclear magnetic resonance (ss-NMR) and Wide Angle X-ray Diffraction (WAXD) techniques. This insect, which typically dwells in freshwater riverbeds and streams, uses silk fibers as a strong and sticky nanoadhesive material to construct cocoons and cases out available debris. Conformation-sensitive 13C chemical shifts and 31P chemical shift anisotropy (CSA) information strongly support a unique protein motif in which phosphorylated serine- rich repeats (pSX)4 complex with di- and trivalent cations to form rigid nanocrystalline β-sheets. Additionally, it is illustrated through 31P NMR and WAXD data that these nanocrystalline structures can be reversibly formed, and depend entirely on the presence of the stabilizing cations.
Nanofiber silks produced by webspinners (order Embioptera) were also studied herein. This work addresses discrepancies in the literature regarding fiber diameters and tensile properties, revealing that the nanofibers are about 100 nm in diameter, and are stronger (around 500 MPa mean ultimate stress) than previous works suggested. Fourier-transform Infrared Spectroscopy (FT-IR), NMR and WAXD results find that approximately 70% of the highly repetitive glycine- and serine-rich protein core is composed of β-sheet nanocrystalline structures. In addition, FT-IR and Gas-chromatography mass spectroscopy (GC-MS) data revealed a hydrophobic surface coating rich in long-chain lipids. The effect of this surface coating was studied with contact angle techniques; it is shown that the silk sheets are extremely hydrophobic, yet due to the microstructural and nanostructural details of the silk surface, are surprisingly adhesive to water.
The molecular structure of caddisfly larval silk from the species Hesperophylax consimilis was characterized using solid-state nuclear magnetic resonance (ss-NMR) and Wide Angle X-ray Diffraction (WAXD) techniques. This insect, which typically dwells in freshwater riverbeds and streams, uses silk fibers as a strong and sticky nanoadhesive material to construct cocoons and cases out available debris. Conformation-sensitive 13C chemical shifts and 31P chemical shift anisotropy (CSA) information strongly support a unique protein motif in which phosphorylated serine- rich repeats (pSX)4 complex with di- and trivalent cations to form rigid nanocrystalline β-sheets. Additionally, it is illustrated through 31P NMR and WAXD data that these nanocrystalline structures can be reversibly formed, and depend entirely on the presence of the stabilizing cations.
Nanofiber silks produced by webspinners (order Embioptera) were also studied herein. This work addresses discrepancies in the literature regarding fiber diameters and tensile properties, revealing that the nanofibers are about 100 nm in diameter, and are stronger (around 500 MPa mean ultimate stress) than previous works suggested. Fourier-transform Infrared Spectroscopy (FT-IR), NMR and WAXD results find that approximately 70% of the highly repetitive glycine- and serine-rich protein core is composed of β-sheet nanocrystalline structures. In addition, FT-IR and Gas-chromatography mass spectroscopy (GC-MS) data revealed a hydrophobic surface coating rich in long-chain lipids. The effect of this surface coating was studied with contact angle techniques; it is shown that the silk sheets are extremely hydrophobic, yet due to the microstructural and nanostructural details of the silk surface, are surprisingly adhesive to water.
ContributorsAddison, John Bennett (Author) / Yarger, Jeffery L (Thesis advisor) / Holland, Gregory P (Thesis advisor) / Wang, Xu (Committee member) / Ros, Robert (Committee member) / Arizona State University (Publisher)
Created2014
Description
Membrane-based gas separation is promising for efficient propylene/propane (C3H6/C3H8) separation with low energy consumption and minimum environment impact. Two microporous inorganic membrane candidates, MFI-type zeolite membrane and carbon molecular sieve membrane (CMS) have demonstrated excellent thermal and chemical stability. Application of these membranes into C3H6/C3H8 separation has not been well investigated. This dissertation presents fundamental studies on membrane synthesis, characterization and C3H6/C3H8 separation properties of MFI zeolite membrane and CMS membrane.
MFI zeolite membranes were synthesized on α-alumina supports by secondary growth method. Novel positron annihilation spectroscopy (PAS) techniques were used to non-destructively characterize the pore structure of these membranes. PAS reveals a bimodal pore structure consisting of intracrystalline zeolitic micropores of ~0.6 nm in diameter and irregular intercrystalline micropores of 1.4 to 1.8 nm in size for the membranes. The template-free synthesized membrane exhibited a high permeance but a low selectivity in C3H6/C3H8 mixture separation.
CMS membranes were synthesized by coating/pyrolysis method on mesoporous γ-alumina support. Such supports allow coating of thin, high-quality polymer films and subsequent CMS membranes with no infiltration into support pores. The CMS membranes show strong molecular sieving effect, offering a high C3H6/C3H8 mixture selectivity of ~30. Reduction in membrane thickness from 500 nm to 300 nm causes an increase in C3H8 permeance and He/N2 selectivity, but a decrease in the permeance of He, N2 and C3H6 and C3H6/C3H8 selectivity. This can be explained by the thickness dependent chain mobility of the polymer film resulting in final carbon membrane of reduced pore size with different effects on transport of gas of different sizes, including possible closure of C3H6-accessible micropores.
CMS membranes demonstrate excellent C3H6/C3H8 separation performance over a wide range of feed pressure, composition and operation temperature. No plasticization was observed at a feed pressure up to 100 psi. The permeation and separation is mainly controlled by diffusion instead of adsorption. CMS membrane experienced a decline in permeance, and an increase in selectivity over time under on-stream C3H6/C3H8 separation. This aging behavior is due to the reduction in effective pore size and porosity caused by oxygen chemisorption and physical aging of the membrane structure.
MFI zeolite membranes were synthesized on α-alumina supports by secondary growth method. Novel positron annihilation spectroscopy (PAS) techniques were used to non-destructively characterize the pore structure of these membranes. PAS reveals a bimodal pore structure consisting of intracrystalline zeolitic micropores of ~0.6 nm in diameter and irregular intercrystalline micropores of 1.4 to 1.8 nm in size for the membranes. The template-free synthesized membrane exhibited a high permeance but a low selectivity in C3H6/C3H8 mixture separation.
CMS membranes were synthesized by coating/pyrolysis method on mesoporous γ-alumina support. Such supports allow coating of thin, high-quality polymer films and subsequent CMS membranes with no infiltration into support pores. The CMS membranes show strong molecular sieving effect, offering a high C3H6/C3H8 mixture selectivity of ~30. Reduction in membrane thickness from 500 nm to 300 nm causes an increase in C3H8 permeance and He/N2 selectivity, but a decrease in the permeance of He, N2 and C3H6 and C3H6/C3H8 selectivity. This can be explained by the thickness dependent chain mobility of the polymer film resulting in final carbon membrane of reduced pore size with different effects on transport of gas of different sizes, including possible closure of C3H6-accessible micropores.
CMS membranes demonstrate excellent C3H6/C3H8 separation performance over a wide range of feed pressure, composition and operation temperature. No plasticization was observed at a feed pressure up to 100 psi. The permeation and separation is mainly controlled by diffusion instead of adsorption. CMS membrane experienced a decline in permeance, and an increase in selectivity over time under on-stream C3H6/C3H8 separation. This aging behavior is due to the reduction in effective pore size and porosity caused by oxygen chemisorption and physical aging of the membrane structure.
ContributorsMa, Xiaoli (Author) / Lin, Jerry (Thesis advisor) / Alford, Terry (Committee member) / Chan, Candace (Committee member) / Arizona State University (Publisher)
Created2015
Description
As the use of engineered nanomaterials (ENMs) in consumer products becomes more common, the amount of ENMs entering wastewater treatment plants (WWTPs) increases. Investigating the fate of ENMs in WWTPs is critical for risk assessment and pollution control. The objectives of this dissertation were to (1) quantify and characterize titanium (Ti) in full-scale wastewater treatment plants, (2) quantify sorption of different ENMs to wastewater biomass in laboratory-scale batch reactors, (3) evaluate the use of a standard, soluble-pollutant sorption test method for quantifying ENM interaction with wastewater biomass, and (4) develop a mechanistic model of a biological wastewater treatment reactor to serve as the basis for modeling nanomaterial fate in WWTPs. Using titanium (Ti) as a model material for the fate of ENMs in WWTPs, Ti concentrations were measured in 10 municipal WWTPs. Ti concentrations in pant influent ranged from 181 to 3000 µg/L, and more than 96% of Ti was removed, with effluent Ti concentrations being less than 25 µg/L. Ti removed from wastewater accumulated in solids at concentrations ranging from 1 to 6 µg Ti/mg solids. Using transmission electron microscopy, spherical titanium oxide nanoparticles with diameters ranging from 4 to 30 nm were found in WWTP effluents, evidence that some nanoscale particles will pass through WWTPs and enter aquatic systems. Batch experiments were conducted to quantify sorption of different ENM types to activated sludge. Percentages of sorption to 400 mg TSS/L biomass ranged from about 10 to 90%, depending on the ENM material and functionalization. Natural organic matter, surfactants, and proteins had a stabilizing effect on most of the ENMs tested. The United States Environmental Protection Agency's standard sorption testing method (OPPTS 835.1110) used for soluble compounds was found to be inapplicable to ENMs, as freeze-dried activated sludge transforms ENMs into stable particles in suspension. In conjunction with experiments, we created a mechanistic model of the microbiological processes in membrane bioreactors to predict MBR, extended and modified this model to predict the fate of soluble micropollutants, and then discussed how the micropollutant fate model could be used to predict the fate of nanomaterials in wastewater treatment plants.
ContributorsKiser, Mehlika Ayla (Author) / Westerhoff, Paul K (Thesis advisor) / Rittmann, Bruce E. (Committee member) / Hristovski, Kiril D (Committee member) / Arizona State University (Publisher)
Created2011
Description
Titanium dioxide (TiO2) nanomaterial use is becoming more prevalent as is the likelihood of human exposure and environmental release. The goal of this thesis is to develop analytical techniques to quantify the level of TiO2 in complex matrices to support environmental, health, and safety research of TiO2 nanomaterials. A pharmacokinetic model showed that the inhalation of TiO2 nanomaterials caused the highest amount to be absorbed and distributed throughout the body. Smaller nanomaterials (< 5nm) accumulated in the kidneys before clearance. Nanoparticles of 25 nm diameter accumulated in the liver and spleen and were cleared from the body slower than smaller nanomaterials. A digestion method using nitric acid, hydrofluoric acid, and hydrogen peroxide was found to digest organic materials and TiO2 with a recovery of >80%. The samples were measured by inductively coupled plasma-mass spectrometry (ICP-MS) and the method detection limit was 600 ng of Ti. An intratracheal instillation study of TiO2 nanomaterials in rats found anatase TiO2 nanoparticles in the caudal lung lobe of rats 1 day post instillation at a concentration of 1.2 ug/mg dry tissue, the highest deposition rate of any TiO2 nanomaterial. For all TiO2 nanomaterial morphologies the concentrations in the caudal lobes were significantly higher than those in the cranial lobes. In a study of TiO2 concentration in food products, white colored foods or foods with a hard outer shell had higher concentrations of TiO2. Hostess Powdered Donettes were found to have the highest Ti mass per serving with 200 mg Ti. As much as 3.8% of the total TiO2 mass was able to pass through a 0.45 um indicating that some of the TiO2 is likely nanosized. In a study of TiO2 concentrations in personal care products and paints, the concentration of TiO2 was as high as 117 ug/mg in Benjamin Moore white paint and 70 ug/mg in a Neutrogena sunscreen. Greater than 6% of Ti in one sunscreen was able to pass through a 0.45 um filter. The nanosized TiO2 in food products and personal care products may release as much as 16 mg of nanosized TiO2 per individual per day to wastewater.
ContributorsWeir, Alex Alan (Author) / Westerhoff, Paul K (Thesis advisor) / Hristovski, Kiril (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2011
Description
Glycosaminoglycans (GAGs) are a class of complex biomolecules comprised of linear, sulfated polysaccharides whose presence on cell surfaces and in the extracellular matrix involve them in many physiological phenomena as well as in interactions with pathogenic microbes. Decorin binding protein A (DBPA), a Borrelia surface lipoprotein involved in the infectivity of Lyme disease, is responsible for binding GAGs found on decorin, a small proteoglycan present in the extracellular matrix. Different DBPA strains have notable sequence heterogeneity that results in varying levels of GAG-binding affinity. In this dissertation, the structures and GAG-binding mechanisms for three strains of DBPA (B31 and N40 DBPAs from B. burgdorferi and PBr DBPA from B. garinii) are studied to determine why each strain has a different affinity for GAGs. These three strains have similar topologies consisting of five α-helices held together by a hydrophobic core as well as two long flexible segments: a linker between helices one and two and a C-terminal tail. This structural arrangement facilitates the formation of a basic pocket below the flexible linker which is the primary GAG-binding epitope. However, this GAG-binding site can be occluded by the flexible linker, which makes the linker a negative regulator of GAG-binding. ITC and NMR titrations provide KD values that show PBr DBPA binds GAGs with higher affinity than B31 and N40 DBPAs, while N40 binds with the lowest affinity of the three. Work in this thesis demonstrates that much of the discrepancies seen in GAG affinities of the three DBPAs can be explained by the amino acid composition and conformation of the linker. Mutagenesis studies show that B31 DBPA overcomes the pocket obstruction with the BXBB motif in its linker while PBr DBPA has a retracted linker that exposes the basic pocket as well as a secondary GAG-binding site. N40 DBPA, however, does not have any evolutionary modifications to its structure to enhance GAG binding which explains its lower affinity for GAGs. GMSA and ELISA assays, along with NMR PRE experiments, confirm that structural changes in the linker do affect GAG-binding and, as a result, the linker is responsible for regulating GAG affinity.
ContributorsMorgan, Ashli M (Author) / Wang, Xu (Thesis advisor) / Allen, James (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2015
Description
Drinking water filtration using reverse osmosis (RO) membranes effectively removes salts and most other inorganic, organic, and microbial pollutants. RO technologies are utilized at both the municipal and residential scale. The formation of biofilms on RO membranes reduces water flux and increases energy consumption. The research conducted for this thesis involves In-Situ coating of silver, a known biocide, on the surface of RO membranes. This research was adapted from a protocol developed for coating flat sheet membranes with silver nanoparticles, and scaled up into spiral-wound membranes that are commonly used at the residential scale in point-of-use (POU) filtration systems. Performance analyses of the silver-coated spiral-wound were conducted in a mobile drinking water treatment system fitted with two POU units for comparison. Five month-long analyses were performed, including a deployment of the mobile system. In addition to flux, salt rejection, and other water quality analyses, additional membrane characterization tests were conducted on pristine and silver-coated membranes.
For flat sheet membranes coated with silver, the surface charge remained negative and contact angle remained below 90. Scaling up to spiral-wound RO membrane configuration was successful, with an average silver-loading of 1.93 g-Ag/cm2. Results showed the flux of water through the membrane ranged from 8 to 13 liters/m2*hr. (LMH) operating at 25% recovery during long-term of operation. The flux was initially decreased due to the silver coating, but no statistically significant differences were observed after 14 days of operation (P < 0.05). The salt rejection was also not effected due to the silver coating (P < 0.05). While 98% of silver was released during long-term studies, the silver release from the spiral-wound membrane was consistently below the secondary MCL of 100 ppb established by the EPA, and was consistently below 5 ppb after two hours of operation. Microbial assays in the form of heterotrophic plate counts suggested there was no statistically significant difference in the prevention of biofouling formation due to the silver coating (P < 0.05). In addition to performance tests and membrane characterizations, a remote data acquisition system was configured to remotely monitor performance and water quality parameters in the mobile system.
For flat sheet membranes coated with silver, the surface charge remained negative and contact angle remained below 90. Scaling up to spiral-wound RO membrane configuration was successful, with an average silver-loading of 1.93 g-Ag/cm2. Results showed the flux of water through the membrane ranged from 8 to 13 liters/m2*hr. (LMH) operating at 25% recovery during long-term of operation. The flux was initially decreased due to the silver coating, but no statistically significant differences were observed after 14 days of operation (P < 0.05). The salt rejection was also not effected due to the silver coating (P < 0.05). While 98% of silver was released during long-term studies, the silver release from the spiral-wound membrane was consistently below the secondary MCL of 100 ppb established by the EPA, and was consistently below 5 ppb after two hours of operation. Microbial assays in the form of heterotrophic plate counts suggested there was no statistically significant difference in the prevention of biofouling formation due to the silver coating (P < 0.05). In addition to performance tests and membrane characterizations, a remote data acquisition system was configured to remotely monitor performance and water quality parameters in the mobile system.
ContributorsZimmerman, Sean (Author) / Westerhoff, Paul K (Thesis advisor) / Sinha, Shahnawaz (Committee member) / Perreault, Francois (Committee member) / Arizona State University (Publisher)
Created2017