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Tuning the Hydrophilicity of Electrospun Membranes for Pretreatment in Water Filtration

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Obtaining access to clean water is a global problem that is becoming more important with increasing population and advancing technology. Desalination through reverse osmosis (RO) is a promising technology takes advantage of the global supply of saline water to augment

Obtaining access to clean water is a global problem that is becoming more important with increasing population and advancing technology. Desalination through reverse osmosis (RO) is a promising technology takes advantage of the global supply of saline water to augment its limited freshwater reservoirs. To increase RO membrane performance, the feedwater is pretreated to take any excess pollutants out before the desalination. These pretreatment membranes are susceptible to fouling, which reduces efficiency and drives up costs of the overall process. Increasing the hydrophilicity of these membranes would reduce fouling, and electrospinning is a production method of pretreatment membranes with the capability to control hydrophilicity. This work explores how the composition of electrospun fibrous membranes containing blends of hydrophilic and hydrophobic polymers affects membrane characteristics such as wettability as well as filtration performance. Nonwoven, nanoscale membranes were prepared using electrospinning with a targeted application of pretreatment in water filtration. Using a rotating collector, electrospun mats of hydrophobic poly(vinyl chloride) (PVC) and hydrophilic poly(vinyl alcohol) (PVA) were simultaneously deposited from separate polymer solutions, and their polymer compositions were then characterized using Fourier Transform Infrared (FTIR) spectra. The data did not reveal a reliable correlation established between experimental control variables like flow rate and membrane composition. However, when the membranes' hydrophilicity was analyzed using static water contact angle measurements, a trend between PVA content and hydrophilicity was seen. This shows that the hypothesis of increasing PVA content to increase hydrophilicity is reliable, but with the current experimental design the PVA content is not controllable. Therefore, the primary future work is making a new experimental setup that will be able to better control membrane composition. Filtration studies to test for fouling and size exclusion will be performed once this control is obtained.

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2018-12

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Improving Offset Electrospinning for the Tendon-Bone Junction

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The tendon-bone junction, also known as the enthesis, is crucial for properly transferring mechanical loadings during physical activity. During injury, current restoration procedures are insufficient for properly restoring tissue function. Thus, it is paramount to design alternative tissue engineered scaffolds

The tendon-bone junction, also known as the enthesis, is crucial for properly transferring mechanical loadings during physical activity. During injury, current restoration procedures are insufficient for properly restoring tissue function. Thus, it is paramount to design alternative tissue engineered scaffolds to act as a template to the injured region and a regenerative response for tendon-bone repair. Thus, we utilized an offset electrospinning technique to fabricate a scaffold that mimics the native biochemical gradients present within the tendon-bone junction. To improve chemical gradient resolution, we implemented both insulating and conductive shields during offset electrospinning. Polycaprolactone fibers with either rhodamine or fluorescein were used to measure the scaffold fluorescent strength with distance. Without shields, at an offset of 4 cm, the chemical gradient resolution for rhodamine and fluorescein were 2.5 cm and 6.0 cm, respectively. During implementation of insulating shields, the gradient resolution for rhodamine and fluorescein improved to 2 cm and 0.5 cm, respectively. Lastly, grounded conductive shields improved gradient resolution for rhodamine and fluorescein to 1.0 cm and 1.5 cm, respectively.

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2019-05

Heterogeneous Catalysis for Organic Reactions

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This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel

This honors thesis is focused on two separate catalysis projects conducted under the mentorship of Dr. Javier Pérez-Ramírez at ETH Zürich. The first project explored ethylene oxychlorination over supported europium oxychloride catalysts. The second project investigated alkyne semihydrogenation over nickel phosphide catalysts. This work is the subject of a publication of which I am a co-author, as cited below.

Project 1 Abstract: Ethylene Oxychlorination
The current two-step process for the industrial process of vinyl chloride production involves CuCl2 catalyzed ethylene oxychlorination to ethylene dichloride followed by thermal cracking of the latter to vinyl chloride. To date, no industrial application of a one-step process is available. To close this gap, this work evaluates a wide range of self-prepared supported CeO2 and EuOCl catalysts for one-step production of vinyl chloride from ethylene in a fixed-bed reactor at 623 773 K and 1 bar using feed ratios of C2H4:HCl:O2:Ar:He = 3:3 6:1.5 6:3:82 89.5. Among all studied systems, CeO2/ZrO2 and CeO2/Zeolite MS show the highest activity but suffer from severe combustion of ethylene, forming COx, while 20 wt.% EuOCl/γ-Al2O3 leads to the best vinyl chloride selectivity of 87% at 15.6% C2H4 conversion with complete suppression of CO2 formation and only 4% selectivity to CO conversion for over 100 h on stream. Characterization by XRD and EDX mapping reveals that much of the Eu is present in non-active phases such as Al2Eu or EuAl4, indicating that alternative synthesis methods could be employed to better utilize the metal. A linear relationship between conversion and metal loading is found for this catalyst, indicating that always part of the used Eu is available as EuOCl, while the rest forms inactive europium aluminate species. Zeolite-supported EuOCl slightly outperforms EuOCl/γ Al2O3 in terms of total yield, but is prone to significant coking and is unstable. Even though a lot of Eu seems locked in inactive species on EuOCl/γ Al2O3, these results indicate possible savings of nearly 16,000 USD per kg of catalyst compared to a bulk EuOCl catalyst. These very promising findings constitute a crucial step for process intensification of polyvinyl chloride production and exploring the potential of supported EuOCl catalysts in industrially-relevant reactions.

Project 2 Abstract: Alkyne Semihydrogenation
Despite strongly suffering from poor noble metal utilization and a highly toxic selectivity modifier (Pb), the archetypal catalyst applied for the three-phase alkyne semihydrogenation, the Pb-doped Pd/CaCO3 (Lindlar catalyst), is still being utilized at industrial level. Inspired by the very recent strategies involving the modification of Pd with p-block elements (i.e., S), this work extrapolates the concept by preparing crystalline metal phosphides with controlled stoichiometry. To develop an affordable and environmentally-friendly alternative to traditional hydrogenation catalysts, nickel, a metal belonging to the same group as Pd and capable of splitting molecular hydrogen has been selected. Herein, a simple two-step synthesis procedure involving nontoxic precursors was used to synthesize bulk nickel phosphides with different stoichiometries (Ni2P, Ni5P4, and Ni12P5) by controlling the P:Ni ratios. To uncover structural and surface features, this catalyst family is characterized with an array of methods including X-ray diffraction (XRD), 31P magic-angle nuclear magnetic resonance (MAS-NMR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Bulk-sensitive techniques prove the successful preparation of pure phases while XPS analysis unravels the facile passivation occurring at the NixPy surface that persists even after reductive treatment. To assess the characteristic surface fingerprints of these materials, Ar sputtering was carried out at different penetration depths, reveling the presence of Ni+ and P-species. Continuous-flow three-phase hydrogenations of short-chain acetylenic compounds display that the oxidized layer covering the surface is reduced under reaction conditions, as evidenced by the induction period before reaching the steady state performance. To assess the impact of the phosphidation treatment on catalytic performance, the catalysts were benchmarked against a commercial Ni/SiO2-Al2O3 sample. While Ni/SiO2-Al2O3 presents very low selectivity to the alkene (the selectivity is about 10% at full conversion) attributed to the well-known tendency of naked nickel nanoparticles to form hydrides, the performance of nickel phosphides is highly selective and independent of P:Ni ratio. In line with previous findings on PdxS, kinetic tests indicate the occurrence of a dual-site mechanism where the alkyne and hydrogen do not compete for the same site.

This work is the subject of a publication of which I am a co-author, as cited below.

D. Albani; K. Karajovic; B. Tata; Q. Li; S. Mitchell; N. López; J. Pérez-Ramírez. Ensemble Design in Nickel Phosphide Catalysts for Alkyne Semi-Hydrogenation. ChemCatChem 2019. doi.org/10.1002/cctc.201801430

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2019-05

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Ionic Liquids to Lab: Investigating an Emerging Water Filtration Challenge to Engineering Nanofiber Polymer Membranes as Next-Generation Solutions for Water Purification

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The following thesis documents a two-fold approach to investigate challenges pertaining to water purification, first through a meta-analysis of ionic liquid toxicity, then through experimentation aimed at developing water pre-treatment membranes. Ionic liquids (ILs) are salts with low melting points,

The following thesis documents a two-fold approach to investigate challenges pertaining to water purification, first through a meta-analysis of ionic liquid toxicity, then through experimentation aimed at developing water pre-treatment membranes. Ionic liquids (ILs) are salts with low melting points, typically liquid at room temperature. Several extraordinary physical attributes, e.g. low viscosity, high conductivity, low to no vapor pressure, etc., and seemingly unlimited combinations available, have pushed IL research to the forefront of many research fronts. Concerns are raised as ionic liquids are rushed into commercial production without sufficient environmental regulation. Research has shown that the chemicals are in fact toxic, yet have developed a reputation for being “green” chemicals due to select physical attributes and applications. The meta-analysis discussed focuses on industry perception of ionic liquid toxicity through a patent review, and considers toxicity of ILs comparatively against other chemical families with well-established toxicity. The meta-analysis revealed that the total patent literature pertaining to ILs (n=3358) resulted in 112 patents that addressed the toxicity of ILs, and notably few (n=17) patents defined ILs as toxic, representing only 0.51% of the evaluated body of work on intellectual property claims. Additionally, toxicity of ionic liquids is comparable to that of other chemical families.
The objective of the experimentation was to explore the effect of crosslinker chain length on the morphology of nanofiber mats. Specifically, poly(vinyl alcohol (PVA) was electrospun into nanofiber mats and poly(ethylene) glycol bis(carboxylic acid) (PEG diacid) was used as the crosslinking agent. As-spun fibers had average fiber diameter of 70 ± 30 nm with an average pore size of 0.10 ± 0.16 μm^2. The fiber diameter for the mats crosslinked with the shorter PEG diacid (Mn = 250) increased to 110 ± 40 nm with an average pore size of 0.11 ± 0.04 μm^2. The mats crosslinked with the longer PEG diacid (Mn = 600) had fiber diameters of 180 ± 10 nm with an average pore size 0.01 ± 0.02 μm^2.

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2016-05

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Controlling Calcium Binding on NorHA Scaffolds using a Biomineralization Peptide

Description

The tendon-bone junction is essential for allowing humans to transfer mechanical loads during activities. When injury does occur to this important area, current surgical techniques improperly bypass important physical and chemical gradients and do not restore proper function. It is

The tendon-bone junction is essential for allowing humans to transfer mechanical loads during activities. When injury does occur to this important area, current surgical techniques improperly bypass important physical and chemical gradients and do not restore proper function. It is essential to create tissue engineered scaffolds that create proper models for the region and induce healing responses for repair. To advance research into these scaffolds, electrospinning fibers and hydrogels made of norbornene functionalized hyaluronic acid (NorHA) were used to promote bone growth by adhering calcium to the material. To further improve calcium adherence, which is indicative of bone regions, a mineralization peptide was allowed to soak through the fibers. NorHA proved to be a suitable material for biomineralization experiments, showing slow calcium adherence within the first hour before accelerating in adherence over 24 hours in both fibers and hydrogels. When the mineralization peptide was implemented calcium adherence on fibers increased nearly eight times within the first 15 minutes of experimentation.

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2020-05

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Electrospinning Stimuli-Responsive Fibers at the Nanoscale as Functional Drug Delivery Mats

Description

The objective of this research is to create biodegradable mats with tunable characteristics such as fiber diameter and surface area. The drug delivery mats enable spatially controlled delivery of disease-specific therapeutics. Using a large electric potential to draw fibers

The objective of this research is to create biodegradable mats with tunable characteristics such as fiber diameter and surface area. The drug delivery mats enable spatially controlled delivery of disease-specific therapeutics. Using a large electric potential to draw fibers from a solution flowing at a specific rate, the polymer fibers reach a grounded target several inches away. The biodegradable polymer used in this study was poly(lactic acid-co-glycolic acid) (PLGA). PLGA solutions ranging from 0.5 to 27 wt.% were prepared by dissolving the block copolymer in a solvent mixture containing tetrahydrofuran (THF) and dimethylformamide (DMF) at a 3:1 weight ratio. They were then electrospun at needle-to-target distances of 7, 14, and 18 cm and rates ranging from 0.8 to 4 mL/h. The range of voltage used was between 8 – 15 kV, which was based on the observation of the formation of a Taylor cone, largely affected by on the environment and weather (e.g., temperature and humidity in the lab). A 27 wt.% PLGA solution, electrospun at 1 mL/h at a voltage of 11.25 kV and needle-to-target distance of 14 cm produced uniform fibers with an average fiber diameter of 0.985 m. All other parameters outside the range given created beaded fibers. In addition, solution rheology was performed on some of the PLGA solution to measure viscosity, which is directly correlated to the fiber diameter of the electrospun mats. Observing the impact of solvent on fiber spinning and fiber diameter brings about many positive results in developing fully characterized and well-understood fibrous mats for drug delivery. The nanoscale fibers will be used as drug delivery mats and, therefore, the biodegradation kinetics of the polymers will be studied. Next, parameters of the polymers as well as the polymeric mats will be correlated to the degradation-mediated release of small molecule therapeutics (e.g., peptides, drugs, etc.) such that time-resolved dosing profiles can be created.

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2016-12