Τα μαγνητικά νανοσωματίδια συνήθως σχηματίζουν συλλογές, είτε με τυχαία είτε με διατεταγμένη δομή, που παρουσιάζουν νέες μαγνητικές ιδιότητες, διαφοροποιημένες σε σχέση με αυτές των συμπαγών μαγνητικών υλικών. Οι ιδιότητες των συστημάτων μαγνητικών νανοσωματιδίων έχουν αποτελέσει αντικείμενο εκτεταμένης πειραματικής και θεωρητικής έρευνας για πολλά χρόνια και έχουν δείξει τις δυνατότητες των τεχνολογικών εφαρμογών τους. Στην παρούσα εργασία μελετήθηκαν διάφορα μεσοσκοπικά μοντέλα συλλογών μαγνητικών νανοσωματιδίων. Νέοι υπολογιστικοί κώδικες αναπτύχτηκαν που χρησιμοποιούν τον αλγόριθμο Metropolis Monte Carlo για την μελέτη της μαγνητικής συμπεριφοράς των συλλογών των νανοσωματιδίων. Πρώτα μελετάμε το ρόλο των αλληλεπιδράσεων μεταξύ των νανοσωματιδίων και της μορφολογία στην μαγνητική συμπεριφορά των πυκνών συλλογών των νανοσωματιδίων σιδήρου (Fe) με συγκεντρώσεις πολύ πάνω από το κατώφλι διήθησης. Στα μοντέλα μας κάθε απλό νανοσωματίδιο απεικονίζεται από ένα τρισδιάστατο κλασικό μοναδιαίο διάνυσμα σπιν. Οι προσομοιώσεις μας έδειξαν ότι ο ισχυρός ανταγωνισμός μεταξύ της ενέργειας ανισοτροπίας και της ενέργειας ανταλλαγής σε μη-ομοιόμορφες πυκνές συλλογές έχει σαν αποτέλεσμα τον ασαφή καθορισμό των ζεύξεων των μαγνητικών ροπών των νανοσωματιδίων και δημιουργεί οροπέδια (plateau) και απότομα βήματα (steps), τα οποία υποδηλώνουν μια ξαφνική, συλλογική αναστροφή των σπιν για χαμηλής και ενδιάμεσής ισχύος διπολικές δυνάμεις. Η σύγκριση μεταξύ των αποτελεσμάτων των προσομοιώσεων μας και των πειραματικών αποτελεσμάτων για τις πυκνές συλλογές νανοσωματιδίων Fe επιβεβαιώνει το σπουδαίο ρόλο των περιοχών με διαφορετικές συγκεντρώσεις, που έχουν σαν αποτέλεσμα το σχηματισμό συσσωματωμάτων διαφορετικών μεγεθών, και δείχνει ότι η μαγνητική συμπεριφορά καθορίζεται από την μορφολογία του συστήματος. Ακολούθως μελετάμε την ταυτόχρονη συνεισφορά μεταξύ των εγγενών ιδιοτήτων και των συλλογικών φαινομένων. Πρώτα θεωρούμε την επιφανειακή συνεισφορά κάθε μαγνητικού νανοσωματιδίου της συλλογής. Παράγονται αναλυτικές εκφράσεις για τη μαγνήτιση για ασθενείς διπολικές αλληλεπιδράσεις σε χαμηλές συγκεντρώσεις. Η μελέτη μας βασίζεται στην θερμοδυναμική θεωρία διαταραχών για το ισοδύναμο μοντέλο του ενός σπιν ανά σωμάτιο όπου ένα νανοσωματίδιο αναπαρίσταται από την μακροσκοπική μαγνητική ροπή του, λαμβάνοντας υπόψη τα επιφανειακά φαινόμενα κάθε νανοσωματιδίου. Οι προσεγγιστικές αναλυτικές εκφράσεις για την μαγνήτιση συγκρίνονται με προσομοιώσεις Monte Carlo και καθορίζεται το εύρος της ισχύος τους. Οι υπολογισμοί μας δείχνουν ότι η μαγνήτιση επηρεάζεται από την ανισοτροπία των νανοσωματιδίων και το σχήμα της συλλογής και ότι, σε όλες τις περιπτώσεις, το αποτέλεσμα του όρου δεύτερης τάξης της διπολικής αλληλεπίδρασης στη θεωρία διαταραχών είναι η μείωση της μαγνήτισης. Κατόπιν, παρουσιάζουμε μια νέα προσέγγιση για την προσομοίωση των μαγνητικών ιδιοτήτων μεγάλων συλλογών σύνθετων μαγνητικών νανοσωματιδίων με μορφολογία σιδηρομαγνητικού πυρήνα/αντισιδηρομαγνητικού φλοιού. Οι προσομοιώσεις με τη μέθοδο Monte Carlo των συλλογών μαγνητικών νανοσωματιδίων με σύνθετη μορφολογία πυρήνα/φλοιού αναπαράγει τις τάσεις που παρατηρούνται πειραματικά για τα φαινόμενα διεπαφής αλλά και για τα φαινόμενα που οφείλονται στις αλληλεπιδράσεις. Η μεσοσκοπική μέθοδος βασίζεται στη μείωση του αριθμού των αναπαριστώμενων σπιν στον ελάχιστο αριθμό που είναι απαραίτητος για να περιγράψει την μαγνητική δομή των νανοσωματιδίων εισάγοντας τον επαρκή αριθμό των παραμέτρων ανταλλαγής μεταξύ των διαφορετικών σπιν. Για τέσσερα σωματίδια σιδηρομαγνητικού πυρήνα/αντισιδηρομαγνητικού φλοιού, οι τάσεις του μεσοσκοπικού μοντέλου είναι συνεπείς με τις πλήρεις Monte-Carlo προσομοιώσεις. Επιπλέον τα πλεονεκτήματα της προσέγγισης αποδεικνύεται με την προσομοίωση μεγάλων συλλογών νανοσωματιδίων Co/CoO που αναπαράγει ικανοποιητικά τα πειραματικά αποτελέσματα σε αυτό το σύστημα. / Magnetic nanoparticles usually form assemblies, either with random or ordered structure, which exhibit magnetic behaviour different from that of the bulk magnetic materials. The properties of the magnetic nanoparticles systems have been the subject of extensive experimental and theoretical research for many years and have demonstrated their potential technological application. In the present work, mesoscopic models of different types of magnetic nanoparticle assemblies with different morphologies have been studied. New Computational Codes have been developed with the implementation of the Metropolis Monte Carlo algorithm to study the magnetic behavior of the nanoparticles assemblies. First we study the role of interparticle interactions and the morphology in the magnetic behavior of dense assemblies of Fe nanoparticles with concentration well above the percolation threshold. We model every single nanoparticle with a three-dimensional classical unit spin vector. Our simulations showed that the strong competition between the anisotropy energy and exchange energy in non-uniform dense assemblies results in a frustration of the nanoparticles moments coupling and creates plateaus and abrupt steps, which indicate a sudden, collective spin reversal, for low and intermediate dipolar strengths. The comparison between our simulation results and the experimental findings dense assemblies of Fe nanoparticles confirmed the important role of the areas with different concentration, which results to the formation of clusters of different sizes and that magnetic behaviour is determined by the system morphology. Next we study the interplay between intrinsic properties and collective effects in assemblies. We first consider the surface contribution in each ferromagnetic nanoparticle in the assembly. Analytical expressions for the magnetization are obtained for weak dipolar interactions in dilute assemblies. Our study is based on thermodynamic perturbation theory for the effective macrospin model where a nanoparticle is represented by its macroscopic magnetic moment, taking into account surface effects of each nanoparticle. The approximate analytical expressions for the magnetization are compared to Monte Carlo simulations and their range of validity is established. Our calculations show that the magnetization is influenced by the nanoparticle anisotropy and the shape of the assembly and that in all cases the effect of the second order dipolar interaction term of the perturbation theory is the reduction of the magnetization. Finally, we present a novel approach to simulate the magnetic properties of large assemblies of bi-magnetic FM core/AFM shell nanoparticles. Monte-Carlo simulations of core/shell nanoparticle assemblies have reproduced the main trends observed experimentally for the the interface effects together with the interaction effects. Our mesoscopic method is based on reducing the amount of simulated spins to the minimum number necessary to describe the magnetic structure of the particles and introducing the adequate exchange parameters between the different spins. For four ferromagnetic/antiferromagnetic core/shell nanoparticles, the trends of the mesoscopic model are consistent with full Monte-Carlo simulations. Moreover, the validity of the approach is demonstrated by the simulation of large arrays of Co/CoO nanoparticles which satisfactorily reproduces experimental results in this system.

This doctoral thesis analyses the concept of risk and how it functions as an organizing principle of discourse, paying close attention to actual linguistic practice.           Article 1 analyses the concepts of risk, safety and security and their relations based on corpus data (the Corpus of Contemporary American English). Lexical, grammatical and semantic contexts of the nouns risk, safety and security, and the adjectives risky, safe and secure are analysed and compared. Similarities and differences are observed, suggesting partial synonymy between safety (safe) and security (secure) and semantic opposition to risk (risky). The findings both support and contrast theoretical assumptions about these concepts in the literature.           Article 2 analyses the concepts of risk and danger and their relation based on corpus data (in this case the British National Corpus). Frame semantics is used to explore the assumptions of the sociologist Niklas Luhmann (and others) that the risk concept presupposes decision-making, while the concept of danger does not. Findings partly support and partly contradict this assumption.           Article 3 analyses how newspapers represent risk and causality. Two theories are used: media framing and the philosopher John Mackie’s account of causality. A central finding of the study is that risks are “framed” with respect to causality in several ways (e.g. one and the same type of risk can be presented as resulting from various causes). Furthermore, newspaper reporting on risk and causality vary in complexity. In some articles, risks are presented without causal explanations, while in other articles, risks are presented as results from complex causal conditions. Considering newspaper reporting on an aggregated overall level, complex schemas of causal explanations emerge.           Article 4 analyses how phenomena referred to by the term nano (e.g. nanotechnology, nanoparticles and nanorobots) are represented as risks in Swedish newspaper reporting. Theoretically, the relational theory of risk and frame semantics are used. Five main groups of nano-risks are identified based on the risk object of the article: (I) nanotechnology; (II) nanotechnology and its artefacts (e.g. nanoparticles and nanomaterials); (III) nanoparticles, without referring to nanotechnology; (IV) non-nanotechnological nanoparticles (e.g. arising from traffic); and (V) nanotechnology and nanorobots. Various patterns are explored within each group, concerning, for example, what is considered to be at stake in relation to these risk objects, and under what conditions. It is concluded that Swedish patterns of newspaper reporting on nano-risks follow international trends, influenced by scientific assessment, as well as science fiction.           Article 5 analyses the construction and negotiation of risk in the Swedish controversy over the use of antibacterial silver in health care and consumer products (e.g. sports clothes and equipment). The controversy involves several actors: print and television news media, Government and parliament, governmental agencies, municipalities, non-government organisations, and companies. In the controversy, antibacterial silver is claimed to be a risk object that negatively affects health, the environment, and sewage treatment industry (objects at risk). In contrast, such claims are denied. Antibacterial silver is even associated with the benefit of mitigating risk objects (e.g. bacteria and micro-organisms) that threaten health and the environment (objects at risk). In other words, both sides of the controversy invoke health and the environment as objects at risk. Three strategies organising risk communication are identified: (i) representation of silver as a risk to health and the environment; (ii) denial of such representations; and (iii) benefit association, where silver is construed to mitigate risks to health and the environment. / Avhandlingen analyserar begreppet risk och hur detta begrepp strukturerar diskurs. Ett centralt intresse för analysen är faktisk språkanvändning.           I den första artikeln analyseras de engelska begreppen risk, safety and security och deras relation. Analysen bygger på korpusdata (the Corpus of Contemporary American English). Lexikala och grammatiska kontexter för substantiven risk, safety och security och adjektiven risky, safe och secure analyseras och jämförs. Både likheter och skillnader identifieras vilka i stort bekräftar att safety (safe) och security (secure) är synonymer och i sin tur motsatser (antonymer) till risk (risky). Studien stödjer flera tidigare antaganden om dessa begrepp inom forskningslitteraturen, men motsäger andra.           I den andra artikeln analyseras de engelska begreppen risk och danger och deras relation baserat på korpusdata (the British National Corpus). Ramsemantik (eng. frame semantics) används för att undersöka antagandet att begreppet risk förutsätter beslutsfattande, medan begreppet danger inte gör det. Studien stödjer delvis detta antagande, men visar också på problem med antagandet.           I den tredje artikeln analyseras hur nyhetspress framställer risk och orsak-verkansamband (kausalitet). Två teorier används. För det första används teorin om medias ”inramning” av händelser (eng. media framing). För det andra används filosofiska perspektiv på kausala beskrivningar. En huvudsaklig slutsats är att risker framställs på många olika sätt med avseende på kausalitet. Exempelvis kan en och samma risk framställas som ett resultat av flera olika orsaker. Vidare framställer nyhetspress riskers kausalitet med olika grader av komplexitet. I vissa tidningsartiklar presenteras risker utan några kausala förklaringar. I andra tidningsartiklar presenteras risker som resultat av komplexa orsak-verkansamband. Om man betraktar nyhetsrapporteringen om risker på en övergripande nivå, så framträder en komplex bild av riskers orsakssamband.           I den fjärde artikeln analyseras framställningar av fenomen som benämns med morfemet nano, exempelvis nanoteknologi, nanomaterial och nanorobotar. Frågan som besvaras är på vilket sätt sådana fenomen framställs som risker i svensk nyhetspress. Teoretiskt utgår studien från den relationella teorin om risk och ramsemantik. Baserat på vilka fenomen som framställs som riskobjekt (eller hot) i tidningsartiklar, identifieras fem grupper av nanorisker: (I) nanoteknologi, (II) nanoteknologi och dess produkter (t.ex. nanopartiklar och nanomaterial), (III) nanopartiklar (utan referens till nanoteknologi), (IV) nanopartiklar som inte är resultat av nanoteknologi (utan istället uppstår t.ex. i trafiken) och (V) nanoteknologi och nanorobotar. För varje grupp undersöks vidare mönster i framställningen av dessa risker, exempelvis, vad som beskrivs som hotat av dessa riskobjekt och under vilka förutsättningar. Studiens empiriska observationer stödjer tidigare forskning om hur nanorisker rapporteras i nyhetspress internationalt. Rapporteringen av nanorisker är influerad av vetenskapliga riskbedömningar, men också av science fiction.           I den femte artikeln analyseras en kontrovers kring användningen av antibakteriellt silver inom sjukvården och i konsumentartiklar som exempelvis träningskläder och sportutrustning. Fokus för artikeln är hur risker uppfattas i den svenska debatten som inbegriper nyhetsmedia (press och TV), regering och riksdag, myndigheter, kommuner, intresseorganisationer och företag. Vissa aktörer menar att silver är ett riskobjekt som påverkar olika värden på ett negativt sätt, till exempel, folkhälsan, miljön, och avloppsreningsindustrin. Andra aktörer förnekar dessa påståenden. De menar till och med att silver har fördelar som att motverka risker som hotar folkhälsan och miljön. Med andra ord åberopar båda sidorna av kontroversen hälsa och miljö som värden viktiga att skydda. Slutligen identifieras tre strategier för riskkommunikation som tillämpas i kontroversen: (i) framställningen av silver som en miljö- och hälsorisk, (ii) förnekande av dessa påståenden, och (iii) nyttoassociationer där silver framställs som något som motverkar miljö- och hälsorisker. / <p>QC 20160127</p>

The primary purpose of this work was to evaluate the capability of nanoparticles to transform electromagnetic energy at microwave frequencies into therapeutic heating. Targeted nanoparticles, in conjunction with microwave irradiation, can increase the temperatures of the targeted area over the peripheral region. Therefore, to become clinically viable, microwave absorbing nanoparticles must first be identified, and a system to monitor the treatment must be developed. In this study, ultrasound temperature imaging was used to monitor the temperature of deep lying structures. First, a material-dependent quantity to correlate the temperature induced changes in ultrasound images (i.e. apparent time shifts) to differential temperatures was gathered for a tissue-mimicking phantom, porcine longissimus dorsi muscle, and porcine fat. Then microwave nanoabsorbers were identified using an infrared radiometer. The determined nanoabsorbers were then injected into ex-vivo porcine longissimus dorsi muscle tissue. Ultrasound imaging frames were gathered during microwave treatment of the inoculated tissue. Finally, the ultrasound frames were analyzed using the correlation between temperature and apparent shifts in ultrasound for porcine muscle tissue. The outcome was depth-resolved temperature profiles of the ex-vivo porcine muscle during treatment. The results of this study show that magnetite is a microwave nanoabsorber that increases the targeted temperature of microwave hyperthermia treatments. Overall, there is clinical potential to use microwave nanoabsorbers to increase the efficiency of microwave hyperthermia treatments. / text

Non-oxidative dehydrogenation of hydrocarbons is an attractive alternative route for the production of CO- and CO2-free hydrogen. It will satisfy a major requirement for successful utilization of polymer electrolyte membrane (PEM) fuel cells (< 10 ppm CO) and sequestering carbon as a potentially valuable by-product, carbon nanotubes (CNTs). Due to the deposition of carbon on the surface of catalyst particles during the reaction, catalyst performance, life-time, and purification of the generated carbon product, are significant issues to solve in order to make the process practically feasible. The scope of this thesis includes: the development of novel Fe, Ni, and Fe-Ni catalysts supported on a Mg(Al)O support to achieve improved catalytic performance with easily-purified CNTs; evaluation of catalysts for ethane/methane dehydrogenation at moderate reaction temperatures; and study of activation and deactivation mechanisms by a variety of characterization techniques including TEM, HRTEM, XRD, Mössbauer spectroscopy, and x-ray absorption fine structure (XAFS) spectroscopy. The Mg(Al)O support was prepared by calcination of synthetic MgAl-hydrotalcite with a Mg to Al ratio of 5. The catalysts were prepared either by conventional incipient wetness method or by a novel nanoparticle impregnation method, where the monodisperse catalyst nanoparticles were prepared in advance by thermal decomposition of a metal-organic complex in an organic-phase solution and then dispersed onto the Mg(Al)O support. Dehydrogenation of undiluted methane was conducted in a fix-bed plug-flow reactor. Before reaction, the catalysts were activated by reduction in hydrogen. Fe-based catalysts exhibit a higher hydrogen yield at temperature above 600ºC compared with monometallic Ni catalyst. FeNi-9 nm/Mg(Al)O, Fe-10 nm/Mg(Al)O and Fe-5 nm/ Mg(Al)O nanoparticle catalysts show much improved performance and longer life-times compared with the corresponding FeNi IW/Mg(Al)O and Fe IW/Mg(Al)O catalysts prepared by incipient wetness. 10 nm is the optimum particle size for methane dehydrogenation. Addition of Ni to Fe forming a bimetallic FeNi alloy catalyst enhances the catalytic performance at the temperatures below 650ºC. Metallic Fe, Ni, FeNi alloy and Fe-Ni-C alloy, unstable iron carbide are all catalytically active components. Catalysts deactivation is due to the carbon encapsulation. The carbon products are in the form of stack-cone CNTs (SCNTs) and multi-walled CNTs (MWNTs), depending on the reaction temperature and catalyst composition. The growth of CNTs follows a tip growth mechanism and the purity of cleaned CNTs is more than 99.5%.

Neuropeptidases are responsible for degradation of signaling peptides in the central nervous system and periphery. Some neuropeptidases have also been shown to play a role as part of the cell’s hydrolytic machinery responsible for breaking down proteins and peptides into amino acids, and these enzymes therefore influence small peptide availability for antigen presentation. A better understanding of how neuropeptidases recognize their substrates could lead to therapeutics that modulate the activity of these important enzymes. Alternatively, re-engineering these enzymes to selectively hydrolyze undesirable peptides could make them attractive as therapeutics themselves. A key question in understanding the activity of these enzymes is how they are able to recognize a variety of seemingly unrelated amino acid sequences as cleavage sites. We are investigating the basis for this general substrate recognition in neuropeptidases using thimet oligopeptidase (TOP) as a model. Crystal structures of TOP in complex with a variety of substrates and inhibitors shed light on the mechanisms underlying substrate recognition and pave the way for re-targeting substrate recognition in these enzymes. Nano test tube particles have been proposed as a means of delivering therapeutics such as enzymes. However, the template synthesis method for nano test tube production does not produce therapeutic quantities. In order to take full advantage of re-engineered neuropeptidases a new method for nano test tube synthesis has been developed. We show that a non-destructive template synthesis methodology can be applied to produce nano test tube particles in quantities useful for therapeutic enzyme immobilization.

Technological limitations have prevented interrogation and manipulation of many signaling pathways in model and living systems required for the development of diagnostic and therapeutic modalities in diseases, such as cancer. Liposome-supported plasmon resonant gold nanoshells are biologically inspired composite structures, in which the liposome allows for the encapsulation of substances, and the plasmon resonant structure facilitates rapid release of encapsulated contents upon laser light illumination. As shown in this work, we overcome current limitations in cellular manipulation using plasmon resonant gold-coated liposomes in conjunction with light-activated release to achieve accurate probing of complex cellular responses. Development toward this goal was demonstrated with four specific aims. The first specific aim was to develop a computational model of heat diffusion to investigate the light-induced heating of gold-coated liposomes. This model was used to optimize the photothermal process for release of an encapsulated payload. The second aim was to demonstrate encapsulation and on-demand release of molecules in a spectrally-controlled manner, where plasmon resonant nanoparticles only release content upon illumination with a wavelength of light matching their plasmon resonance band. The third specific aim was to demonstrate that this release mechanism can be used in a biological setting to deliver a peptide and extracellularly activate surface membrane receptors with single-cell spatial and high temporal resolution. The fourth specific aim further refined the level of spatial and temporal control of payload release using gold-coated liposomes with optical trapping to demonstrate mirco-manipulation of liposome movement and rapid content release to enable accurate perturbation of cellular functions in response to released compounds. Through this work, we have developed an experimental system with the potential for the delivery and localized release of an encapsulated agent with high spatial and temporal resolution. This on-demand release system is compatible with a broad range of molecules and uses biologically safe near-infrared light. In combination with the spectral tunability of these plasmon resonant nanoshells and spectrally-selective release, this technology may allow for interrogation of complex and diverse signaling pathways in living tissues or their models with unprecedented spatial and temporal control.

Increasing use of engineered nanomaterials presents concerns as some nanoparticles appear to be harmful to both human health and the environment. Effective treatment methods are required to remove problematic nanoparticles from (waste)water streams. Porous media filtration, commonly used for the removal of particulate matter, shows promise for nanoparticle treatment. The goal of this work is to investigate the potential of porous media filtration for the abatement of nanoparticles from aqueous waste streams. To this end, an automated method was developed that allows real-time and in-situ monitoring of nanoparticle transport and retention in porous media using online measurement of UV-visible absorbance or fluorescence. Development of fluorescent-core nano-silica (n-SiO₂) in controllable sizes provided an excellent tracer for nanoparticle transport in porous media. Measurement of n-SiO₂ by destructive techniques is complicated by high natural Si background levels. Fluorescence monitoring enables real-time measurement, facilitating rapid evaluation of n-SiO₂ transport. Synthesized n-SiO₂ remain in their primary sizes making an evaluation of the behavioral change of particles due to transition into the "nano" range possible. A comparison of the role of particle size on transport in porous media displayed the importance of particle number concentration as the dominance of site-specific adsorption may be obscured by simple mass concentration evaluation.T he effectiveness of different bed materials, namely, sand, activated carbon (AC), and diatomaceous earth (DE), for the removal of TiO₂ nanoparticles (n-TiO₂) from aqueous streams was investigated. DE proved promising for n-TiO₂ capture shown by its high bed capacity (33.8 mg TiO₂ g⁻¹(medium)) compared to AC (0.23 mg TiO₂ g⁻¹(medium)) or sand (0.004 mg TiO₂ g⁻¹(medium)). The presence of organic and synthetic contaminants produced varying effects on n-TiO₂ retention, mostly due to either enhanced electrostatic or steric interactions. Application of a process simulator combining physical straining with site-specific interactions, delineating physisorption from chemisorption and diffusion limited interactions, enabled the accurate fit of n-TiO₂ transport in sand, AC and DE. The fitting process revealed the advantage of DE due to increased physisorption and physical straining of n-TiO₂. Modeling of this system afforded the elucidation of controlling retention mechanisms and provides a basis for future scaling and system design.

<p>The ability of photocatalytic nanoparticles (NPs) to produce reactive oxygen species (ROS) has inspired research into several new applications and technologies, including water purification, contaminant remediation, and self-cleaning surface coatings. As a result, NPs continue to be incorporated into a wide variety of increasingly complex products. With the increased use of NPs and nano-enabled products and their subsequent disposal, NPs will make their way into the environment. Currently, many unanswered questions remain concerning how changes to the NP surface chemistry that occur in natural waters will impact reactivity. This work seeks to investigate potential influences on photoreactivity – specifically the impact of functionalization, the influence of anions, and interactions with biological objects - so that ROS generation in natural aquatic environments may be better understood.</p><p>To this aim, titanium dioxide nanoparticles (TiO2) and fullerene nanoparticles (FNPs) were studied in terms of their reactive endpoints: ROS generation measured through the use of fluorescent or spectroscopic probe compounds, virus and bacterial inactivation, and contaminant degradation. Physical characterization of NPs included light scattering, electron microscopy and electrophoretic mobility. These systematic investigations into the effect of functionalization, sorption, and aggregation on NP aggregate structure, size, and reactivity improve our understanding of trends that impact nanoparticle reactivity.</p><p>Engineered functionalization of FNPs was shown to impact NP aggregation, ROS generation, and viral affinity. Fullerene cage derivatization can lead to a greater affinity for the aqueous phase, smaller mean aggregate size, and a more open aggregate structure, favoring greater rates of ROS production. At the same time however, fullerene derivatization also decreases the 1O2 quantum yield and may either increase or decrease the affinity for a biological surface. These results suggest that the biological impact of fullerenes will be influenced by changes in the type of surface functionalization and extent of cage derivatization, potentially increasing the ROS generation rate and facilitating closer association with biological targets.</p><p>Investigations into anion sorption onto the surface of TiO2 indicate that reactivity will be strongly influenced by the waters they are introduced into. The type and concentration of anion impacted both aggregate state and reactivity to varying degrees. Specific interactions due to inner sphere ligand exchange with phosphate and carbonate have been shown to stabilize NPs. As a result, waters containing chloride or nitrate may have little impact on inherent reactivity but will reduce NP transport via aggregation, while waters containing even low levels of phosphate and carbonate may decrease “acute” reactivity but stabilize NPs such that their lifetime in the water column is increased.</p><p>Finally, ROS delivery in a multicomponent system was studied under the paradigm of pesticide degradation. The presence of bacteria or chlorpyrifos in solution significantly decreased bulk ROS measurements, with almost no OH detected when both were present. However, the presence of bacteria had no observable impact on the rate of chlorpyrifos degradation, nor chlorpyrifos on bacterial inactivation. These results imply that investigating reactivity in simplified systems may significantly over or underestimate photocatalytic efficiency in realistic environments, depending on the surface affinity of a given target.</p><p>This dissertation demonstrates that the reactivity of a system is largely determined by NP surface chemistry. Altering the NP surface, either intentionally or incidentally, produces significant changes in reactivity and aggregate characteristics. Additionally, the photocatalytic impact of the ROS generated by a NP depends on the characteristics of potential targets as well as on the characteristics of the NP itself. These are complicating factors, and the myriad potential exposure conditions, endpoints, and environmental systems to be considered for even a single NP highlight the need for functional assays that employ environmentally relevant conditions if risk assessments for engineered NPs are to be made in a timely fashion so as not to be outpaced by, or impede, technological advances.</p> / Dissertation

© Springer Science+Business Media Dordrecht 2016 / Reducing AgNO3 by glucose at basic pH coated the surface of silica spheres with a high density of hemispherical silver nanoparticles (average diameter 3.2±1 nm). A much lower silver concentration than is standard favored heterogeneous nucleation of silver on the silica surface at the expense of homogeneous nucleation in solution. The slow growth rate of the nuclei promoted the formation of discrete silver particles rather than a continuous shell. Based on scanning electron microscopy and transmission electron microscopy, the surface coverage of silver seed particles was as high as 25% at 10 °C without prior functionalization of the silica. The particles were composed of metallic silver based on x-ray photoelectron spectroscopy. There was a sharp increase in the silver surface coverage and decrease in the particle size when the temperature was raised from 5 °C to 10 °C and the amount of silica was decreased from 0.2 to 0.025 V/V. The size was controlled by the diffusion barrier through the ion shell surrounding the silica spheres and by maintaining reaction conditions where the particles on the surface compete for silver.

Metal nanoparticles have received much interest for their application in catalysis due to high surface-to-volume ratios resulting in more available active sites. Ideally these catalysts are heterogeneous and allow for facile separation from the catalytic reaction mixture making them ideal for industrial application. Dispersed metal nanoparticles are explored due to their high reactivity in solution and are stabilized by surfactants and polymers. However, it is difficult to determine whether or not a catalyst is truly heterogeneous as a certain degree of leaching from the metal nanoparticle is inevitable. Determining the mechanisms involved in nanocatalysis is also a challenge. In this study, a series of dispersed palladium nanocatalysts in the Suzuki reaction with phenylboronic acid and bromobenzene were characterized before and after catalysis to determine what changes occur. Samples where characterized before and after the catalytic reaction by XPS, SEM, and EDS to monitor changes in particle size and composition. Reaction mixtures after catalysis were analyzed by ICP-MS for leached palladium species to determine if concentrations were high enough for homogeneous catalysis to take place. The dispersed palladium nanoparticles studied experienced growth during the catalytic process and a significant amount of leaching. XPS analysis indicates the presence of aromatic species on the particle surface after the catalytic reaction. The aromatic species is likely biphenyl, the product of the catalytic reaction, as the presence of boron and bromine was not found in XPS and EDS analysis.