Synthesis of supported metal nanoparticle catalysts using ligand assisted methods

The synthesis and characterization methods of metal nanoparticles (NPs) have advanced greatly in the last few decades, allowing an increasing understanding of structure-property-performance relationships. However, the role played by the ligands used as stabilizers for metal NPs synthesis or for NPs immobilization on solid supports has been underestimated. Here, we highlight some recent progress in the preparation of supported metal NPs with the assistance of ligands in solution or grafted on solid supports, a modified deposition-reduction method, with special attention to the effects on NPs size, metal-support interactions and, more importantly, catalytic activities. After presenting the general strategies in metal NP synthesis assisted by ligands grafted on solid supports, we highlight some recent progress in the deposition of pre-formed colloidal NPs on functionalized solids. Another important aspect that will be reviewed is related to the separation and recovery of NPs. Finally, we will outline our personal understanding and perspectives on the use of supported metal NPs prepared through ligand-assisted methods.

Drag reduction phenomenon in viscous oil-water dispersed pipe flow: Experimental investigation and phenomenological modeling

An experimental study on drag-reduction phenomenon in dispersed oil-water flow has been performed in a 26-mm-i.d. Twelve meter long horizontal glass pipe. The flow was characterized using a novel wire-mesh sensor based on capacitance measurements and high-speed video recording. New two-phase pressure gradient, volume fraction, and phase distribution data have been used in the analysis. Drag reduction and slip ratio were detected at oil volume fractions between 10 and 45% and high mixture Reynolds numbers, and with water as the dominant phase. Phase-fraction distribution diagrams and cross-sectional imaging of the flow suggested the presence of a higher amount of water near to the pipe wall. Based on that, a phenomenology for explaining drag reduction in dispersed flow in a flow situation where slip ratio is significant is proposed. A simple phenomenological model is developed and the agreement between model predictions and data, including data from the literature, is encouraging. (c) 2011 American Institute of Chemical Engineers AIChE J, 2012

Composição química de aguardentes de cana-de-açúcar fermentadas por diferentes cepas de levedura Saccharomyces cerevisiae

The aim of this study was to evaluate the chemical composition of sugar cane spirits, fermented by different commercial Saccharomyces cerevisiae yeast strains and double distilled by pot still. Sugar cane juices were separately fermented by yeasts CA-11, Y-904, BG-1, PE-2, SA-1 and CAT-1 and distilled by pot still according to the methodology used for whisky production. The alcoholic liquids from first and second distillations were analyzed for concentrations of ethanol, volatile acidity, aldehydes, esters, furfural, higher alcohols and methanol. The sugar cane spirits derived from fermentation by the different yeast strains presented distinct chemical compositions.

Heats of mixing using an isothermal titration calorimeter: Associated thermal effects

[EN] The correct determination of the energy generated or absorbed in the sample cell of an Isothermal Titration Calorimeter (ITC) requires a thorough analysis of the calorimetric signal. This means the identification and quantification of any thermal effect inherent to the working method. In this work, it is carried out a review on several thermal effects, studied by us in previous work, and which appear when an ITC is used for measuring the heats of mixing of liquids in a continuous mode. These effects are due to: (i) the difference between the temperature of the injected liquid and the temperature of the mixture during the mixing process, (ii) the increase of the liquid volume located in the mixing cell and (iii) the stirring velocity. Besides, methods for the identification and quantification of the mentioned effects are suggested.

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Solvatationsdynamik: lokales Relaxationsverhalten glasbildender Systeme

In dieser Arbeit wurde das lokale Relaxationsverhalten niedermolekularer glasbildender Materialien mit der Methode der Solvatationsdynamik untersucht. Bei dieser Methode werden phosphoreszente Farbstoffe als molekulare Sonden für die lokale Dynamik im Glasbildner eingesetzt. Je nach verwendeter Sonde sind unterschiedliche Eigenschaften zugänglich:Mit Farbstoffen, die ihr Dipolmoment bei optischer Anregung nicht ändern, wird eine mechanische Solvatation gemessen, die die lokale viskoelastische Antwort des Materials widerspiegelt. Mit Farbstoffen, die eine Änderung des Dipolmoments bei optischer Anregung aufweisen,sind zusätzlich lokale dielektrische Eigenschaften des Materials zugänglich, die bei endlicher Polarität des Lösungsmittels dominieren. Das heterogene Relaxationsverhalten des Glasbildners 2-Methyltetrahydrofuran wurde quantitativ untersucht.Auf einem Temperaturbereich, auf dem die mittlere Relaxationszeit um mehr als 4 Dekaden variiert, konnte gezeigt werden, daß die Relaxation lokal rein exponentiell verläuft. Zur Abschätzung von Reichweiteneffekten wurden Solvatationsmessungen in einschränkenden Geometrien in Form von porösen Sol-Gel Gläsern mit Porendurchmessern zwischen 7,5-2,5 nm durchgeführt. Der Einfluß der Beschaffenheit der Porenoberfläche wurde durch Vergleichzwischen der Solvatation in nativen und in silanisierten Gläsern untersucht. Es wurde gezeigt, daß auch in den kleinsten verwendeten silanisierten Poren alle Charakteristika des jeweiligen Bulk-Systems erhalten bleiben.In den nativen porösen Gläsern dagegen führt der Einfluß der stark polaren Oberfläche zu einer Änderung der Dynamik.

Dielektrische Relaxation und Retardation lokaler Prozesse in glasbildenden Materialien

Lokale sekundäre Prozesse in glasbildenden Materialien sind wegen ihrer Wechselwirkung mit der primären Relaxation von besonderem Interesse. Für D-Sorbitol wurde die beta-Relaxation mit drei verschiedenen dielektrischen Meßtechniken untersucht und die Ergebnisse miteinander verglichen. Im Gegensatz zu konventionellen Messungen der dielektrischen Retardation, detektiert eine echte dielektrische Relaxationsmessung den Zerfall des elektrischen Feldes unter der Bedingung einer konstanten dielektrischen Verschiebung. Eine weitere dielektrische Relaxationsmethode ist die Solvatationsdynamik. Sie detektiert die dielektrische Relaxation in der direkten Umgebung eines Farbstoffmoleküls. Die Übereinstimmung der lokal ermittelten und der makroskopisch gemittelten Ergebnisse für den Glaszustand weisen darauf hin, daß die Sekundärrelaxation in D-Sorbitol eine räumlich homogene Eigenschaft ist. Im Gegensatz zu beta-Prozessen anderer Materialien, zeigt nur der abgeschreckte Glaszustand von ortho-Terphenyl einen sekundären Prozeß. Es wurde beobachtet, daß die beta-Amplitude beim Ausheilen langsam abnimmt und im Gleichgewichtszustand der Flüssigkeit oberhalb der Glasübergangstemperatur völlig verschwindet. Viele glasbildende Materialien, wie z. B. Salol zeigen keinen dielektrischen beta-Prozeß. Im Gegensatz zu Messungen mit Standardkühlraten, zeigt eine stark abgeschreckte Salol-Probe eine symmetrische dielektrische Sekundärrelaxation. Diese neuartige Eigenschaft von Salol verschwindet irreversibel, wenn sich die Temperatur der Glasübergangstemperatur nähert.

Monte Carlo-Simulationen zum kritischen Verhalten dünner Ising-Filme

Monte Carlo-Simulationen zum kritischen Verhalten dünnerIsing-Filme Dünne Ising-Filme können als vereinfachtes Modell zurBeschreibung von binären Mischungen oder von Flüssigkeitenin schlitzartigen Kapillaren dienen. Infolge dereingeschränkten Geometrie unterscheidet sich das kritischeVerhalten dieser Systeme signifikant von dem einesBulk-Systems, es kommt zu einem Crossover von zwei- zudreidimensionalem kritischen Verhalten. Zusätzlichverschiebt sich der Phasenübergang in den ungesättigtenBereich, ein Effekt, der als 'capillary condensation'bezeichnet wird. In der vorliegenden Arbeit wurden die kritischenEigenschaften von Ising-Filmen im Rahmen einer MonteCarlo-Simulation untersucht. Zur Verbesserung der Effizienzwurde ein Cluster-Algorithmus verwendet, der um einenGhost-Spin-Term zur Behandlung der Magnetfelder erweitertwar. Bei der Datenanalyse kamen moderneMulti-Histogramm-Techniken zur Anwendung. Für alle untersuchten Schichtdicken konnten kritischeTemperatur und Magnetfeld sehr präzise bestimmt werden. DieSkalenhypothese von Fisher und Nakanishi, die dieVerschiebung des kritischen Punktes gegenüber seinesBulk-Wertes beschreibt, wurde sowohl für Systeme mit freienOberflächen als auch für Systeme mit schwachemOberflächenfeld bestätigt. Der Wert des Gap-Exponenten derOberfläche wurde mit $Delta_1$=0.459(13) in Übereinstimmungmit den Literaturwerten abgeschätzt. Die Observablen Magnetisierung und magnetischeSuszeptibilität sowie deren auf die Oberfläche bezogenenEntsprechungen zeigen kein reines zweidimensionaleskritisches Verhalten. Zu ihrer Beschreibung in der Nähe deskritischen Punktes wurden effektive Exponenten für dieeinzelnen Schichtdicken bestimmt.

Electrode Materials for Ionic Liquid Based-Supercapacitors

The development of safe, high energy and power electrochemical energy-conversion systems can be a response to the worldwide demand for a clean and low-fuel-consuming transport. This thesis work, starting from a basic studies on the ionic liquid (IL) electrolytes and carbon electrodes and concluding with tests on large-size IL-based supercapacitor prototypes demonstrated that the IL-based asymmetric configuration (AEDLCs) is a powerful strategy to develop safe, high-energy supercapacitors that might compete with lithium-ion batteries in power assist-hybrid electric vehicles (HEVs). The increase of specific energy in EDLCs was achieved following three routes: i) the use of hydrophobic ionic liquids (ILs) as electrolytes; ii) the design and preparation of carbon electrode materials of tailored morphology and surface chemistry to feature high capacitance response in IL and iii) the asymmetric double-layer carbon supercapacitor configuration (AEDLC) which consists of assembling the supercapacitor with different carbon loadings at the two electrodes in order to exploit the wide electrochemical stability window (ESW) of IL and to reach high maximum cell voltage (Vmax). Among the various ILs investigated the N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR1(2O1)TFSI) was selected because of its hydrophobicity and high thermal stability up to 350 °C together with good conductivity and wide ESW, exploitable in a wide temperature range, below 0°C. For such exceptional properties PYR1(2O1)TFSI was used for the whole study to develop large size IL-based carbon supercapacitor prototype. This work also highlights that the use of ILs determines different chemical-physical properties at the interface electrode/electrolyte with respect to that formed by conventional electrolytes. Indeed, the absence of solvent in ILs makes the properties of the interface not mediated by the solvent and, thus, the dielectric constant and double-layer thickness strictly depend on the chemistry of the IL ions. The study of carbon electrode materials evidences several factors that have to be taken into account for designing performing carbon electrodes in IL. The heat-treatment in inert atmosphere of the activated carbon AC which gave ACT carbon featuring ca. 100 F/g in IL demonstrated the importance of surface chemistry in the capacitive response of the carbons in hydrophobic ILs. The tailored mesoporosity of the xerogel carbons is a key parameter to achieve high capacitance response. The CO2-treated xerogel carbon X3a featured a high specific capacitance of 120 F/g in PYR14TFSI, however, exhibiting high pore volume, an excess of IL is required to fill the pores with respect to that necessary for the charge-discharge process. Further advances were achieved with electrodes based on the disordered template carbon DTC7 with pore size distribution centred at 2.7 nm which featured a notably high specific capacitance of 140 F/g in PYR14TFSI and a moderate pore volume, V>1.5 nm of 0.70 cm3/g. This thesis work demonstrated that by means of the asymmetric configuration (AEDLC) it was possible to reach high cell voltage up to 3.9 V. Indeed, IL-based AEDLCs with the X3a or ACT carbon electrodes exhibited specific energy and power of ca. 30 Wh/kg and 10 kW/kg, respectively. The DTC7 carbon electrodes, featuring a capacitance response higher of 20%-40% than those of X3a and ACT, respectively, enabled the development of a PYR14TFSI-based AEDLC with specific energy and power of 47 Wh/kg and 13 kW/kg at 60°C with Vmax of 3.9 V. Given the availability of the ACT carbon (obtained from a commercial material), the PYR1(2O1)TFSI-based AEDLCs assembled with ACT carbon electrodes were selected within the EU ILHYPOS project for the development of large-size prototypes. This study demonstrated that PYR1(2O1)TFSI-based AEDLC can operate between -30°C and +60°C and its cycling stability was proved at 60°C up to 27,000 cycles with high Vmax up to 3.8 V. Such AEDLC was further investigated following USABC and DOE FreedomCAR reference protocols for HEV to evaluate its dynamic pulse-power and energy features. It was demonstrated that with Vmax of 3.7 V at T> 30 °C the challenging energy and power targets stated by DOE for power-assist HEVs, and at T> 0 °C the standards for the 12V-TSS and 42V-FSS and TPA 2s-pulse applications are satisfied, if the ratio wmodule/wSC = 2 is accomplished, which, however, is a very demanding condition. Finally, suggestions for further advances in IL-based AEDLC performance were found. Particularly, given that the main contribution to the ESR is the electrode charging resistance, which in turn is affected by the ionic resistance in the pores that is also modulated by pore length, the pore geometry is a key parameter in carbon design not only because it defines the carbon surface but also because it can differentially “amplify” the effect of IL conductivity on the electrode charging-discharging process and, thus, supercapacitor time constant.

Neue Methoden zur Computersimulation von Polymersystemen auf verschiedenen Längenskalen und ihre Anwendungen

In dieser Dissertation stellen wir einen neuen Ansatz zurModellierungvon Polymersystemen vor. Es werden (von methodischer Seiteher) zweiautomatisierte Iterationschemata dazu eingeführt,Kraftfeldparametermesoskopischer Polymersysteme systematisch zu optimieren:DasSimplex-Verfahren und das Struktur-Differenzen-Verfahren. Sowerdendiejenigen Freiheitsgrade aus Polymersystemen eliminiert,die einehohe Auflösung erfordern, was die Modellierung größerersystemeermöglicht. Nach Tests an einfachen Flüssigkeiten werdenvergröberteModelle von drei prototypischen Polymeren (Polyacrylsäure,Polyvinylalkohol und Polyisopren) in unterschiedlichenUmgebungen(gutes Lösungsmittel und Schmelze) entwickelt und ihrVerhalten aufder Mesoskala ausgiebig geprüft. Die zugehörige Abbildung(vonphysikalischer Seite her) so zu gestalten, daß sie dieunverwechselbaren Charakteristiken jedes systems auf diemesoskopischeLängenskala überträgt, stellt eine entscheidende Anforderungan dieautomatisierten Verfahren dar. Unsere Studien belegen, daß mesoskopische Kraftfeldertemperatur- unddichtespezifisch sind und daher bei geändernden Bedingungennachoptimiert werden müssen. Gleichzeitig läßt sichabschätzen, beiwelchen Umgebungsbedingungen dies noch nicht notwendig wird.In allenFällen reichen effektive Paarpotentiale aus, einrealistischesmesoskopisches Modell zu konstruieren. VergröberteSimulationenwerden im Falle der Polyacrylsäure erfolgreich gegenexperimentelleLichtstreudaten getestet. Wir erzielen für Molmassen bis zu300000g/mol eine hervorragende Übereinstimmung für denhydrodynamischenRadius. Unsere Ergebnisse erklären auch Korrekturen zudessenVerhalten als Funktion der Kettenlänge ('Skalenverhalten'). Im Fallevon Polyisopren untersuchen wir sowohl statische als auchdynamischeGrößen und stellen klare Unterschiede unserer Ergebnisse zudeneneines einfachen semi-flexiblen Mesoskalenmodells fest. InderProteinforschung werden aus Datenbanken gewonnene effektivePaarwechselwirkungen dazu verwendet, die freie Energie einesneuensystems vorherzusagen. Wir belegen in einem Exkurs mittelsGittersimulationen, daß es selbst in einfachsten Fällennicht gelingt,dies auch nur qualitativ korrekt zu bewerkstelligen.

Dynamik unterkühlter molekularer Flüssigkeiten in Modenkopplungsapproximation - die Rolle der Orientierungsfreiheitsgrade für den Bosonenpeak

Die von Schilling et al. 1997 aufgestellten molekularenModenkopplungsgleichungen sind für zwei Systeme, dipolareharte Kugeln undharte Rotationsellipsoide, numerisch gelöst worden.In den Kompressibilitätsspektrenund den entsprechenden Korrelationsspektren der beidenSysteme fiel im Vergleich mit den Spektren einfacherFlüssigkeiten einzusätzlicher Peak (bp) auf.Die Position des zusätzlichen Peaks ist etwa eine Dekade unterhalb der Position derHochfrequenzpeaks, also im mesoskopischen Frequenzbereich.In molekularen Flüssigkeiten sind Phasenübergänge derOrientierung derglqq Molekülegrqq möglich.Bei dipolaren harten Kugeln kann ferroelektrische Ordnung,bei hartenEllipsoiden nematische Ordnung auftreten. Als Vorläuferphänomen der Orientierungsordnung bilden sich in den molekularenFlüssigkeiten orientierungsgeordnete Domänen. Die Kurzzeitdynamik dieser Domänen findetauf mesoskopischer Zeitskala statt. In der unterkühlten Flüssigkeit ist die Dynamik aller Modenan die Dynamikdieser Orientierungsmoden gekoppelt. Unsere Untersuchungen zeigen starke Hinweise darauf, dassdiese Kopplung denbp erzeugt.Demnach ist die Streuung nichtlokalisierter longitudinalerakustischer Modenan lokalisierten Orientierungsmoden die Ursache für den bp.hat nahezu keine q-Abhängigkeit und zeigt einenIsotopeneffekt. Weiterhin verglichen wir die Eigenschaften des bp mit denEigenschaften des Bosonenpeaks (BP).Der BP befindet sich in Spektren realer Systeme ebenfallseine Dekadeunterhalb der Hochfrequenzpeaks.Dieser Vergleich und der Vergleich mit den Ergebnissen einerMD-Simulation desHE-Systems ließ uns vermuten, dass es sich bei dem bp und bei dem BP in Spektrenmolekularer Systeme um dasselbe Phänomen handelt.In einem schematischen Modenkopplungsmodell konnte dasVerhalten des bpzusätzlich untersucht werden.

Use of solvents and environmental friendly materials for applications in Green Chemistry

The present Thesis studies three alternative solvent groups as sustainable replacement of traditional organic solvents. Some aspects of fluorinated solvents, supercritical fluids and ionic liquids, have been analysed with a critical approach and their effective “greenness” has been evaluated from the points of view of the synthesis, the properties and the applications. In particular, the attention has been put on the environmental and human health issues, evaluating the eco-toxicity, the toxicity and the persistence, to underline that applicability and sustainability are subjects with equal importance. The “green” features of fluorous solvents and supercritical fluids are almost well-established; in particular supercritical carbon dioxide (scCO2) is probably the “greenest” solvent among the alternative solvent systems developed in the last years, enabling to combine numerous advantages both from the point of view of industrial/technological applications and eco-compatibility. In the Thesis the analysis of these two classes of alternative solvents has been mainly focused on their applicability, rather than the evaluation of their environmental impact. Specifically they have been evaluated as alternative media for non-aqueous biocatalysis. For this purpose, the hydrophobic ion pairing (HIP), which allows solubilising enzymes in apolar solvents by an ion pairing between the protein and a surfactant, has been investigated as effective enzymatic derivatisation technique to improve the catalytic activity under homogeneous conditions in non conventional media. The results showed that the complex enzyme-surfactant was much more active both in fluorous solvents and in supercritical carbon dioxide than the native form of the enzyme. Ionic liquids, especially imidazolium salts, have been proposed some years ago as “fully green” alternative solvents; however this epithet does not take into account several “brown” aspects such as their synthesis from petro-chemical starting materials, their considerable eco-toxicity, toxicity and resistance to biodegradation, and the difficulty of clearly outline applications in which ionic liquids are really more advantageous than traditional solvents. For all of these reasons in this Thesis a critical analysis of ionic liquids has been focused on three main topics: i) alternative synthesis by introducing structural moieties which could reduce the toxicity of the most known liquid salts, and by using starting materials from renewable resources; ii) on the evaluation of their environmental impact through eco-toxicological tests (Daphnia magna and Vibrio fischeri acute toxicity tests, and algal growth inhibition), toxicity tests (MTT test, AChE inhibition and LDH release tests) and fate and rate of aerobic biodegradation in soil and water; iii) and on the demonstration of their effectiveness as reaction media in organo-catalysis and as extractive solvents in the recovery of vegetable oil from terrestrial and aquatic biomass. The results about eco-toxicity tests with Daphnia magna, Vibrio fischeri and algae, and toxicity assay using cultured cell lines, clearly indicate that the difference in toxicity between alkyl and oxygenated cations relies in differences of polarity, according to the general trend of decreasing toxicity by decreasing the lipophilicity. Independently by the biological approach in fact, all the results are in agreement, showing a lower toxicity for compounds with oxygenated lateral chains than for those having purely alkyl lateral chains. These findings indicate that an appropriate choice of cation and anion structures is important not only to design the IL with improved and suitable chemico-physical properties but also to obtain safer and eco-friendly ILs. Moreover there is a clear indication that the composition of the abiotic environment has to be taken into account when the toxicity of ILs in various biological test systems is analysed, because, for example, the data reported in the Thesis indicate a significant influence of salinity variations on algal toxicity. Aerobic biodegradation of four imidazolium ionic liquids, two alkylated and two oxygenated, in soil was evaluated for the first time. Alkyl ionic liquids were shown to be biodegradable over the 6 months test period, and in contrast no significant mineralisation was observed with oxygenated derivatives. A different result was observed in the aerobic biodegradation of alkylated and oxygenated pyridinium ionic liquids in water because all the ionic liquids were almost completely degraded after 10 days, independently by the number of oxygen in the lateral chain of the cation. The synthesis of new ionic liquids by using renewable feedstock as starting materials, has been developed through the synthesis of furan-based ion pairs from furfural. The new ammonium salts were synthesised in very good yields, good purity of the products and wide versatility, combining low melting points with high decomposition temperatures and reduced viscosities. Regarding the possible applications as surfactants and biocides, furan-based salts could be a valuable alternative to benzyltributylammonium salts and benzalkonium chloride that are produced from non-renewable resources. A new procedure for the allylation of ketones and aldehydes with tetraallyltin in ionic liquids was developed. The reaction afforded high yields both in sulfonate-containing ILs and in ILs without sulfonate upon addition of a small amount of sulfonic acid. The checked reaction resulted in peculiar chemoselectivity favouring aliphatic substrates towards aromatic ketones and good stereoselectivity in the allylation of levoglucosenone. Finally ILs-based systems could be easily and successfully recycled, making the described procedure environmentally benign. The potential role of switchable polarity solvents as a green technology for the extraction of vegetable oil from terrestrial and aquatic biomass has been investigated. The extraction efficiency of terrestrial biomass rich in triacylglycerols, as soy bean flakes and sunflower seeds, was comparable to those of traditional organic solvents, being the yield of vegetable oils recovery very similar. Switchable polarity solvents as been also exploited for the first time in the extraction of hydrocarbons from the microalga Botryococcus braunii, demonstrating the efficiency of the process for the extraction of both dried microalgal biomass and directly of the aqueous growth medium. The switchable polarity solvents exhibited better extraction efficiency than conventional solvents, both with dried and liquid samples. This is an important issue considering that the harvest and the dewatering of algal biomass have a large impact on overall costs and energy balance.

2 H-NMR und Viskositätsuntersuchungen zum Studium der molekularen Dynamik unterkühlter Flüssigkeiten unter Hochdruck

In der vorliegenden Arbeit wurde die Druckabhängigkeit der molekularen Dynamik mittels 2H-NMR und Viskositätsmessungen untersucht. Für die Messungen wurde der niedermolekulare organische Glasbildner ortho-Terphenyl (OTP) ausgewählt, da dieser aufgrund einer Vielzahl vorliegender Arbeiten als Modellsubstanz angesehen werden kann. Daneben wurden auch Messungen an Salol durchgeführt.Die Untersuchungen erstreckten sich über einen weiten Druck- und Temperaturbereich ausgehend von der Schmelze bis weit in die unterkühlte Flüssigkeit. Dieser Bereich wurde aufgrund experimenteller Voraussetzungen immer durch eine Druckerhöhung erreicht.Beide Substanzen zeigten druckabhängig ein Verhalten, das dem der Temperaturvariation bei Normaldruck sehr ähnelt. Auf einer Zeitskala der molekularen Dynamik von 10E-9 s bis zu 10E+2 s wurde daher am Beispiel von OTP ein Druck-Temperatur-Zeit-Superpositionsprinzip diskutiert. Zudem konnte eine Temperatur-Dichte-Skalierung mit rho T-1/4 erfolgreich durchgeführt werden. Dies entspricht einem rein repulsiven Potentialverlauf mit rho -12±3 .Zur Entscheidung, ob die Verteilungsbreiten der mittleren Rotationskorrelationszeiten durch Druckvariation beeinflußt werden, wurden auch Ergebnisse anderer experimenteller Methoden herangezogen. Unter Hinzuziehung aller Meßergebnisse kann sowohl eine Temperatur- als auch Druckabhängigkeit der Verteilungsbreite bestätigt werden. Zur Auswertung von Viskositätsdaten wurde ein Verfahren vorgestellt, das eine quantitative Aussage über den Fragilitätsindex von unterkühlten Flüssigkeiten auch dann zuläßt, wenn die Messungen nicht bis zur Glasübergangstemperatur Tg durchgeführt werden. Die Auswertung der druckabhängigen Viskositätsdaten von OTP und Salol zeigt einen sehr differenzierten druckabhängigen Verlauf des Fragilitätsindexes für beide Glasbildner. OTP zeigt zunächst eine leichte Abnahme und danach wieder eine Zunahme des Fragilitätsindexes, dieses Ergebnis wird auch von Simulationsdaten, die der Literatur entnommen wurden, unterstützt. Salol hingegen zeigt zunächst eine deutliche Zunahme und danach eine Abnahme des Fragilitätsindexes. Das unterschiedliche Verhalten der beiden Glasbildner mit ähnlichem Fragilitätsindex bei Normaldruck wird auf die Wasserstoffbrückenbindungen innerhalb von Salol zurückgeführt.

Monte Carlo simulations of Potts glasses

A complete understanding of the glass transition isstill a challenging problem. Some researchers attributeit to the (hypothetical) occurrence of a static phasetransition, others emphasize the dynamical transitionof mode coupling-theory from an ergodic to a non ergodicstate. A class of disordered spin models has been foundwhich unifies both scenarios. One of these models isthe p-state infinite range Potts glass with p>4, whichexhibits in the thermodynamic limit both a dynamicalphase transition at a temperature T_D, and a static oneat T_0 < T_D. In this model every spins interacts withall the others, irrespective of distance. Interactionsare taken from a Gaussian distribution.In order to understand better its behavior forfinite number N of spins and the approach to thethermodynamic limit, we have performed extensive MonteCarlo simulations of the p=10 Potts glass up to N=2560.The time-dependent spin-autocorrelation function C(t)shows strong finite size effects and it does not showa plateau even for temperatures around the dynamicalcritical temperature T_D. We show that the N-andT-dependence of the relaxation time for T > T_D can beunderstood by means of a dynamical finite size scalingAnsatz.The behavior in the spin glass phase down to atemperature T=0.7 (about 60% of the transitiontemperature) is studied. Well equilibratedconfigurations are obtained with the paralleltempering method, which is also useful for properlyestablishing static properties, such as the orderparameter distribution function P(q). Evidence is givenfor the compatibility with a one step replica symmetrybreaking scenario. The study of the cumulants of theorder parameter does not permit a reliable estimation ofthe static transition temperature. The autocorrelationfunction at low T exhibits a two-step decay, and ascaling behavior typical of supercooled liquids, thetime-temperature superposition principle, is observed. Inthis region the dynamics is governed by Arrheniusrelaxations, with barriers growing like N^{1/2}.We analyzed the single spin dynamics down to temperaturesmuch lower than the dynamical transition temperature. We found strong dynamical heterogeneities, which explainthe non-exponential character of the spin autocorrelationfunction. The spins seem to relax according to dynamicalclusters. The model in three dimensions tends to acquireferromagnetic order for equal concentration of ferro-and antiferromagnetic bonds. The ordering has differentcharacteristics from the pure ferromagnet. The spinglass susceptibility behaves like chi_{SG} proportionalto 1/T in the region where a spin glass is predicted toexist in mean-field. Also the analysis of the cumulantsis consistent with the absence of spin glass orderingat finite temperature. The dynamics shows multi-scalerelaxations if a bimodal distribution of bonds isused. We propose to understand it with a model based onthe local spin configuration. This is consistent with theabsence of plateaus if Gaussian interactions are used.

The Dynamics of a Small Model Glass Former as Viewed from Its Potential Energy Landscape

Despite intensive research during the last decades, thetheoreticalunderstanding of supercooled liquids and the glasstransition is stillfar from being complete. Besides analytical investigations,theso-called energy-landscape approach has turned out to beveryfruitful. In the literature, many numerical studies havedemonstratedthat, at sufficiently low temperatures, all thermodynamicquantities can be predicted with the help of the propertiesof localminima in the potential-energy-landscape (PEL). The main purpose of this thesis is to strive for anunderstanding ofdynamics in terms of the potential energy landscape. Incontrast to the study of static quantities, this requirestheknowledge of barriers separating the minima.Up to now, it has been the general viewpoint that thermallyactivatedprocesses ('hopping') determine the dynamics only belowTc(the critical temperature of mode-coupling theory), in thesense that relaxation rates follow from local energybarriers.As we show here, this viewpoint should be revisedsince the temperature dependence of dynamics is governed byhoppingprocesses already below 1.5Tc.At the example of a binary mixture of Lennard-Jonesparticles (BMLJ),we establish a quantitative link from the diffusioncoefficient,D(T), to the PEL topology. This is achieved in three steps:First, we show that it is essential to consider wholesuperstructuresof many PEL minima, called metabasins, rather than singleminima. Thisis a consequence of strong correlations within groups of PELminima.Second, we show that D(T) is inversely proportional to theaverageresidence time in these metabasins. Third, the temperaturedependenceof the residence times is related to the depths of themetabasins, asgiven by the surrounding energy barriers. We further discuss that the study of small (but not toosmall) systemsis essential, in that one deals with a less complex energylandscapethan in large systems. In a detailed analysis of differentsystemsizes, we show that the small BMLJ system consideredthroughout thethesis is free of major finite-size-related artifacts.