Generation of Nanostructured Surfaces by Self-Assembly Strategies for Site-Selective Protein Adsorption

ABSTRACT The aim of this study is to generate nanopatterned surfaces with feature sizes between 10 and 100 nm on large lateral scale in order to investigate confinement effects on the activity of adsorbed enzymes. To achieve this purpose, novel patterning techniques based on colloidal lithography were developed to generate five different types of nanopatterned surfaces: i) metal-semiconductor nanopatterns, ii) charge heterogeneous 2D and 3D nanopatterned polyelectrolyte multilayers (PEMs), iii) gold nanoparticle arrays on charge heterogeneous nanopatterned PEMs, iv) metal-dielectric hybrid nanopatterns, and v) nanopatterned oligo(ethylene)glycol silane self-assembled monolayers (SAMs). All of the fabricated nanopatterned surfaces were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), ellipsometry and UV-visible spectroscopy. Metal-semiconductor nanopatterns and charge heterogeneous 2D and 3D nanopatterned PEMs were chosen for protein adsorption investigations based on their excellent reproducibility and the capability to produce uniform and high density nanopatterns. Specifically, porous metal-semiconductor nanopatterns with 25 nm (type A25) and 60 nm (type A60) adsorption site diameter and honeycomb-like dielectric nanopatterns with 60 nm (type B60) and 100 nm (type B100) adsorption site diameter were fabricated to evaluate the specific enzymatic activity of surface-bound glucose oxidase (GOx). The amount of GOx adsorbed onto these nanopatterned surfaces was quantified by enzyme linked immunosorbent assays (ELISA). The specific activity of GOx on the nanopatterned surfaces was compared to the specific activity of GOx on poly(allyamine hydrochloride) coated non-patterned surfaces and in solution phase. It was found that the confinement of GOx into nano-domains of patterned substrates has a significant effect on protecting the enzymatic activity of GOx. When the adsorption site diameter was selected similar to enzyme size, the activity of the protein was well preserved and only a small loss of activity was observed. This is in line with the observation that proteins tend to unfold and lose their activity upon contact with surfaces which offer sufficient free surface area. We may therefore conclude from the study that geometrical confinement is a promising strategy to overcome this problem and stabilize surface-bound enzymes

Doctor of Philosophy

dissertationJP-10 is a synthetic fuel with high volumetric energy content. One problem with JP-10, is that its combustion kinetics can be too slow for efficient combustion in hypersonic flight applications. Chapter 2 presents a study on the thermal breakdown and catalytic combustion of JP-10 fuel using CeO 2 (ceria) nanoparticles, in a flow tube reactor. In-situ mass spectrometry was used to analyze decomposition products. In the absence of O2, CeO2 efficiently oxidizes JP-10, reducing decomposition onset temperatures by 300 K over that in a clean flow tube. Under conditions with O2 and CeO2 present, oxidation of JP-10 was found to be catalytic; i.e., oxidation is initiated by reaction of JP-10 with CeO2, which is then reoxidized by O2. Boron is of interest as a high energy density fuel as it has one of the highest volumetric heats of combustion known. A major difficulty in getting boron to burn efficiently is that boron surfaces are protected by a native oxide layer. Chapter 3 presents a simple, scalable, one-step, one-pot synthesis method for producing ∼50 nm boron nanoparticles that are largely unoxidized, made soluble in hydrocarbons through oleic acid functionalization, and optionally coated with ceria. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) were used to investigate size distributions, with X-ray photoelectron spectroscopy (XPS) to probe the surface chemistry. Cryogenic methane has been proposed as a fuel for use in hypersonic engines, due to its relatively high energy content; however its poor ignition performance needs to be addressed through use of catalysts. Chapters 4 and 5 investigate the composition, structure, and surface chemistry of several types of Pd/PdO based nano-catalysts designed to be fuel soluble. A combination of high resolution transmission electron microscopy (HRTEM), electron diffraction, scanning transmission electron microscopy/energy dispersive x-ray spectroscopy (STEM/EDX), and XPS were used. In-situ generated particles were found to be primarily crystalline, metallic Pd, in a narrow size distribution around 8 nm. The ignition temperature was lowered ∼150 K by the catalyst, and evidence is presented showing that ignition is correlated with formation of a subnanometer oxidized Pd surface layer at higher temperatures

Laser and other cleaning procedures for aerospace moulds and a study of mould release agents

A selection of cleaning procedures are discussed which may be used to remove epoxide resin flash contamination bonded on metal and carbon fibre reinforced composite mould tooling that is used in the aerospace industry. Laser ablation, dry ice blasting and chemical cleaning using sodium hydride are three cleaning procedures studied in depth and have been used to treat a range of industrially sourced and model substrates, and contaminants. The effectiveness of the different cleaning regimes have been evaluated using Scanning Electron Microscopy, Atomic Force Microscopy, Auger Electron Spectroscopy, X-ray Photoelectron Spectroscopy and other analytical characterisation techniques. The necessity to clean aerospace tooling arises when moulded parts cannot be easily released from mould tooling and this is associated with mould release residues that have built up over a number of moulding cycles and eventually cause the moulding to stick. A comprehensive literature review of non-stick coatings is given and alternative mould non-silicone based release coatings are evaluated using the above analytical techniques. Coatings investigated include; fluoroalkylsilane, fluoropolymers and metal-fluoropolymer composites and the problems and merits associated with each are discussed.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Molecules in Superfluid Helium Nanodroplets

This open access book covers recent advances in experiments using the ultra-cold, very weakly perturbing superfluid environment provided by helium nanodroplets for high resolution spectroscopic, structural and dynamic studies of molecules and synthetic clusters. The recent infra-red, UV-Vis studies of radicals, molecules, clusters, ions and biomolecules, as well as laser dynamical and laser orientational studies, are reviewed. The Coulomb explosion studies of the uniquely quantum structures of small helium clusters, X-ray imaging of large droplets and electron diffraction of embedded molecules are also described. Particular emphasis is given to the synthesis and detection of new species by mass spectrometry and deposition electron microscopy

Properties of Gasification-derived Char and Its Utilization for Catalytic Tar Reforming

Char is a low-value byproduct of biomass gasification and pyrolysis with many potential applications, such as soil amendment and the synthesis of activated carbon. The overall goal of the proposed research was to develop novel methods to use char derived from gasification for high-value applications in syngas conditioning. The first objective was to investigate effects of gasification condition and feedstock on properties of char derived from fluidized bed gasification. Results show that the surface areas of most of the char were 1�10 m2/g and increased as the equivalence ratio increased. Char moisture and fixed carbon contents decreased while ash content increased as equivalence ratio increased. The next objective was to study the properties of sorghum and red cedar char derived from downdraft gasifier. Red cedar char contained more aliphatic carbon and o-alkyl carbon than sorghum char. Char derived from downdraft gasification had higher heating values and lower ash contents than char derived from fluidized bed gasification. The gasification reactivity of red cedar char was higher than that of sorghum char. Then, red cedar char based catalysts were developed with different preparation method to reform toluene and naphthalene as model tars. The catalyst prepared with nickel nitrate was found to be better than that with nickel acetate. The nickel particle size of catalyst impregnated with nickel nitrate was smaller than that of catalyst impregnated with nickel acetate. The particle size of catalyst impregnated with nickel acetate decreased by hydrazine reduction. The catalyst impregnated with nickel nitrate had the highest toluene removal efficiency, which was 70%-100% at 600-800 �C. The presence of naphthalene in tar reduced the catalyst efficiency. The toluene conversion was 36-99% and the naphthalene conversion was 37%-93% at 700-900 �C. Finally, effects of atmosphere and pressure on catalytic reforming of lignin-derived tars over the developed catalyst were investigated. An increase in reaction temperature led to an increase in removal of most tar components except naphthalene. High pressure promoted the catalytic conditioning of lignin tar. Hydrogen promoted the conversion of lignin into non-condensable gas.Biosystems & Agricultural Engineerin

Properties, functionality and potential applications of novel modified iron nanoparticles for the treatment of 2,4,6-Trichlorophenol

2,4,6-trichlorophenol (TCP) is a pervasive carcinogenic water contaminant found in a wide variety of water and waste systems and is a pertinent model compound of broader aromatic organics, specifically organo-halide pesticides. These compounds are persistent in the environment and show resilience to regular water and waste treatment protocols thus warranting the development and implementation of novel treatment materials for improved contaminant removal. Zero-valent iron (ZVI) has demonstrated the ability to remove or degrade a wide variety of inorganic and organic water contaminants, including chlorophenols, and has been widely applied for in-situ groundwater remediation where contamination is often localised in a low-oxygen environment. ZVI’s broader applications in water treatment have remained mainly limited due to corrosion, particle dispersion, and confinement issues in deployment. This work, therefore, explored the development, functionality, and potential application of new modified nZVI materials (nZVI-Osorb) and assessed their potential to improve iron’s intrinsic functionality while also gauging the material’s viability for TCP remediation in water and waste systems. Materials produced in this thesis were prepared utilising three different embedment procedures (1-pot, multiple additions, oxygen-free). All embedment methods resulted in tightly bound composites featuring high surface areas (340.2-449.1 sq. m/g) with net iron composition ranging from 10% to 29.78% by mass. Electron imaging microscopy verified even dispersion of iron throughout the substrate. Composite materials did not exhibit a delayed rate of atmospheric corrosion over nZVI controls evincing an 18% nZVI0 loss per day until reaching a stabilised concentration (7%) after 48 hrs. nZVI-Osorb composites did produce more favourable iron oxide species which remain conducive to electron transfer from core Fe0 atom. After 50 days, a majority of nZVI in nZVI-Osorb had oxidised to maghemite (30%) and magnetite (26%) compared to control nZVI producing 19% and 12% respectively. Unreactive hematite accounted for 47% of the control and just 36% of the composite. While 1-pot embedment allowed the most substantial control over final iron composition, the oxygen-free method allowed the most reliable preservation of initial nZVI0 concentrations through restricted oxidation. Materials generated through oxygen-free embedment were utilised in the following water treatment trials with TCP. Parameters related to sorption and degradation mechanisms of TCP by nZVI-Osorb were tested in aerobic conditions, e.g. surface and potable water. nZVI-Osorb materials demonstrated high extraction capacity for TCP from aqueous solutions (Qe=1286.4 ±13.5 mg TCP/g Osorb, Qe=1253±106.7 mg TCP/g nZVI-Osorb, pH 5.1, 120mg/L TCP) and followed pseudo second order kinetics. In the broader class of chlorophenols, sorptive affinity mirrored partitioning values with highly substituted chlorophenols displaying the highest sorption capacities. Degradation of TCP by nZVI-Osorb or nZVI controls was not observed due to corrosive hindrance and inadequate reductive capacity, suggesting that materials may not be suitable for highly aerated surface and potable water treatment systems. Environmental conditions pertinent to sorption and degradation mechanisms were evaluated to improve understanding and robustness of functionality in low-oxygen applications, such as wastewater and anaerobic digesters, where nZVI-Osorb treatment is anticipated to be advantageous to TCP sorption and methane production. pH was found to influence sorption dramatically. Acidic solutions below 5 found sorption >90%. This capacity was reduced to <30% when pH was raised above TCP pKa value (6.23) to 7 and above. Further trials found a positive effect on TCP sorption (+7.55%) linked to net pH reduction (5.1 to 3.3) with the addition of secondary acids (volatile fatty acids: acetic, propionic, butyric, 3x 100mg/L) commonly found in anaerobic digester systems. Salinity did not affect TCP sorption. The removal of dissolved and atmospheric oxygen increased total sorption (40ppm-+1.94%, 100ppm- +7.93%, 200ppm- +0.89%, 400mg/L- +14.59%) through reduced iron corrosion and the production of favorable iron oxides, but did not facilitate contaminant degradation. Biodegradation mechanisms for TCP have broadly been established, and new research has supported the improved cometabolic degradation of recalcitrant contaminants like TCP and PCP in nZVI-dosed anaerobic digesters. Model anaerobic digester systems (3.9 g/L nZVI-Osorb, 25mg/L TCP, 240 mg/L acetic, 120mg/L propionic, 120mg/L butyric acid) containing bioreactor sludge (62.5%) were observed through standard water quality diagnostics (pH, ORP, COD, head pressure) for 14 days and suggested that nZVI-Osorb did not inhibit cellular processes. Increased electron activity from iron corrosion and hydrogen gas production, increased overall pH and decreased total ORP in these AD systems. TCP degradation by-products (DCP, CP) were detected in dilute concentrations (<0.01 mg/L) with poor recovery by LC-MS/MS. Results suggest that nZVIOsorb may be well-suited additive for AD systems. This study contributes to knowledge of the properties, functionality, and treatment mechanisms of metal-sorbent composites with a model chlorinated aromatic water contaminant in aerobic and anaerobic environments. The work identifies favourable environmental and process conditions to apply these materials in larger scale applications, particularly, anaerobic digestion and provides support for the continued refinement and improvement of nZVI based remediation systems

Particle Formation, Growth and Transport on the Molecular and Submicron Scale

University of Minnesota Ph.D. dissertation.November 2018. Major: Mechanical Engineering. Advisors: Christopher Hogan, Peter McMurry. 1 computer file (PDF); xi, 185 pages.Nanoparticle formation, growth and transport are important topics in several contexts, such as cloud formation, particle synthesis and additive manufacturing. This thesis approaches the subject with a broad perspective from molecular to the micro- scale, utilizing theoretical analysis, computational simulation as well as experiment observations. First, general dynamic equations are non-dimensionalized and applied to simulate aerosol formation and growth in a constant rate reaction reactor. Dimensionless equations lead to results that are independent of condensing species formation rates. The effect of particle sink processes (e.g. evaporation, wall loss, loss to preexisting particles and dilution) and acid-base reactions are systematically investigated. Errors involved with common methods used for deducing particle growth rates from experimental observations are discussed. The results suggest the maximum overestimation error for true particle growth rates occurs when particle nucleation and growth are collision controlled. Second, tandem mobility-mass spectrometry is utilized to understand sorption of organic vapors onto cluster ions. It is found that cluster structure, polarity and the molecular structure of the condensing vapors all influence uptake by cluster ions, qualitatively in agreement with previous activation efficiency measurements for condensational particle counters. Third, nanoparticle transport in an aerosol deposition device is probed with fluid dynamics and particle trajectory simulations. To facilitate particle trajectory simulations, a neural network based drag law is developed that can be applied over a wide range of Knudsen and Mach numbers. Simulation results reveal both particle impaction speeds and particle focusing effects are size dependent, with optimal particle sizes for maximizing particle impaction speed and focusing. With a newly developed framework, mass, momentum and kinetic energy fluxes from particles to the substrate are calculated. It is shown the kinetic energy flux can be above 104 W m-2 for modest aerosol concentrations due to particle focusing. Finally, classification and prediction of different types of lung cell are performed with machine learning algorithms, using the volatile organic compound profiles of different cell populations. These profiles are obtained by a proton transfer reaction mass spectrometer with high resolution. Proper data processing procedures are found to be the key to differentiate cell populations with the measured profiles

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

From surface science to catalysis: lab-scale vacuum deposited catalyst production

This thesis outlines the adaptation of surface techniques to nanoparticle catalyst production. The work covers the scale up of the Matrix Assembly Cluster Source (MACS), the design and development of new apparatus, dubbed the Clean Catalyst Source (CCS) and the effectiveness of catalysts produced by these systems. All samples are characterised using atomic resolution Scanning Transmission Electron Microscopy (STEM). Produced catalysts are compared to those produced by Incipient Wetness Impregnation (IWI) as a model chemical synthesis method where appropriate to highlight the differences between in-vacuum and conventional solvent based production methods. MACS produced Gold and palladium clusters are deposited onto alumina and silica powders using the MACS producing ∼1g of catalyst. Produced samples are tested for their activity in the oxidation of carbon monoxide, the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride, and the selective hydrogenation of 1-pentyne to 1-pentene as desired. All samples demonstrate activity for these reactions with the exception of gold for hydrogenation. MACS samples demonstrate similar activities to impregnated analogues at far lower loadings with cluster beam samples demonstrating high (95%) selectivity to the production of 1-pentene. Samples deposited using the MACS without matrix formation i.e; atomic rather than cluster deposition demonstrate similar structures and indistinguishable catalytic behaviour. As a result of this similar behaviour, a new apparatus was developed and its design; based on direct sputtering of metals onto oxide powders is presented. The system uses a 10mA, 600V ion source to sputter a 150x150mm metal foil target onto a piezo fluidised bed of support particles. These are tipped between covered hoppers to ensure even coating over multiple depositions. 3g of support is coated in 5 minutes, producing ∼1.1±0.4nm metal clusters by surface agglomeration. Binary palladium copper particles are produced by sequential deposition and found to be alloyed with a metallic ratio standard deviation of 0.2. This value can be halved by co-sputtering of compound (as opposed to alloyed) targets, but is not pursued due to the decreased flexibility of such systems. Samples are tested for their activity in the oxidation of carbon monoxide and the selective hydrogenation of 1-pentyne. CCS samples demonstrate similar light off temperatures and selectivities for these reactions when compared with MACS samples indicating that the in vacuum or solvent free formation is dictating catalyst behaviour, as opposed to the cluster formation. Addition of copper to palladium samples results in a small decrease in selectivity contrary to expectations. Minor differences in catalytic behaviour were seen in ∼20% Cu binary particles across other test reactions. Finally a molybdenum sublayer is used as a surface modifier to produce molybdenum nucleated, molybdenum surrounded and molybdenum supported palladium nanoparticles, using a 10m2g−1 alumina support. These samples were tested for their active surface area using carbon monoxide chemisorption and their retention of hydrogen through temperature programmed desorption. Samples are also tested for their activity in the oxidation of carbon monoxide and the selective hydrogenation of 1-pentyne. Samples demonstrate high (95%) selectivity to the formation of 1-pentene as seen previously. Molybdenum containing structures demonstrate a slight activity suppression and associated selectivity increase. Molybdenum surrounded and nucleated particles demonstrate an increased resistance to sintering with little effect on catalytic activity. This work demonstrates the use of a simple technique to quickly produce large (across 30m2) structures for lab scale catalytic testing