Novel routes to metal nanoparticles : electrodeposition and reactions at liquid-liquid interfaces

This thesis considers the nucleation and growth, synthesis, and catalytic application of metallic nanoparticles at liquid|liquid interfaces. It comprises five publications, a previously unpublished synthesis of polymer coated palladium nanoparticles, and an introduction to the relevant literature. Three publications are concerned with electrodeposition of metal nanoparticles at liquid|liquid interfaces. One publication and the results presented here consider the synthesis of silver and palladium colloids by reduction with pyrrole and thiophene monomers. The fifth publication demonstrates the use of gold and palladium colloids as electrocatalysts in two-phase dehalogenation reactions. The literature reviewed serves as an introduction to nanoparticles, liquid|liquid interfaces and electrodeposition studies relevant to the publications and experimental studies presented herein. Nucleation models used are evaluated by numerical means. In the electrodeposition studies, the fundamentals of deposition reactions at liquid|liquid interfaces, involving irreversible Butler-Volmer type growth kinetics and overlap of diffusion fields are developed. The importance of applied potential, particle agglomeration and surface activity on the nucleation process is shown. Small metallic nanoparticles were synthesized in homogeneous media, using novel syntheses involving pyrrole and thiophene derivatives as both reductants and stabilizators. The use of aqueous metal colloids as catalysts for dehalogenation reactions in a two-phase immiscible electrolyte system is demonstrated. Specifically palladium or gold colloids prepared by the citrate reduction method can be negatively charged in a heterogenous two-phase reaction with decamethylferrocene, and subsequently used as an aqueous catalyst for dehalogenation of 2-bromoacetophenone.reviewe

Modification of permeability transition pore arginine(s) by phenylglyoxal derivatives in isolated mitochondria and mammalian cells. Structure-function relationship of arginine ligands.

Methylglyoxal and synthetic glyoxal derivatives react covalently with arginine residue(s) on the mitochondrial permeability transition pore (PTP). In this study, we have investigated how the binding of a panel of synthetic phenylglyoxal derivatives influences the opening and closing of the PTP. Using both isolated mitochondria and mammalian cells, we demonstrate that the resulting arginine-phenylglyoxal adduct can lead to either suppression or induction of permeability transition, depending on the net charge and hydrogen bonding capacity of the adduct. We report that phenylglyoxal derivatives that possess a net negative charge and/or are capable of forming hydrogen bonds induced permeability transition. Derivatives that were overall electroneutral and cannot form hydrogen bonds suppressed permeability transition. When mammalian cells were incubated with low concentrations of negatively charged phenylglyoxal derivatives, the addition of oligomycin caused a depolarization of the mitochondrial membrane potential. This depolarization was completely blocked by cyclosporin A, a PTP opening inhibitor, indicating that the depolarization was due to PTP opening. Collectively, these findings highlight that the target arginine(s) is functionally linked with the opening/closing mechanism of the PTP and that the electric charge and hydrogen bonding of the resulting arginine adduct influences the conformation of the PTP. These results are consistent with a model where the target arginine plays a role as a voltage sensor

Ferromagnetic resonance in ϵ\epsilon-Co magnetic composites

We investigate the electromagnetic properties of assemblies of nanoscale $\epsilon$-cobalt crystals with size range between 5 nm to 35 nm, embedded in a polystyrene (PS) matrix, at microwave (1-12 GHz) frequencies. We investigate the samples by transmission electron microscopy (TEM) imaging, demonstrating that the particles aggregate and form chains and clusters. By using a broadband coaxial-line method, we extract the magnetic permeability in the frequency range from 1 to 12 GHz, and we study the shift of the ferromagnetic resonance with respect to an externally applied magnetic field. We find that the zero-magnetic field ferromagnetic resonant peak shifts towards higher frequencies at finite magnetic fields, and the magnitude of complex permeability is reduced. At fields larger than 2.5 kOe the resonant frequency changes linearly with the applied magnetic field, demonstrating the transition to a state in which the nanoparticles become dynamically decoupled. In this regime, the particles inside clusters can be treated as non-interacting, and the peak position can be predicted from Kittel's ferromagnetic resonance theory for non-interacting uniaxial spherical particles combined with the Landau-Lifshitz-Gilbert (LLG) equation. In contrast, at low magnetic fields this magnetic order breaks down and the resonant frequency in zero magnetic field reaches a saturation value reflecting the interparticle interactions as resulting from aggregation. Our results show that the electromagnetic properties of these composite materials can be tuned by external magnetic fields and by changes in the aggregation structure.Comment: 14 pages, 13 figure

Electrochemically Controlled Proton-Transfer-Catalyzed Reactions at Liquid-Liquid Interfaces: Nucleophilic Substitution on Ferrocene Methanol

The generation of α-ferrocenyl carbocations from ferrocenyl alcohols for SN1 substitution at the water–organic solvent interface is initiated by the transfer of protons into the organic phase. The proton flux, and hence the reaction rate, can be controlled by addition of a suitable “phase-transfer catalyst” anion or by external polarization with a potentiostat, providing a new method for the synthesis of ferrocene derivatives

Nanopartiklar i fasgränsen vätska/vätska

Nanopartikkelien kvanttimekaaniset voivat mahdollistaa äärimmäisen pienien ja nopeiden elektronisten komponenttien valmistuksen. Nanopartikkelien sovellutukset tehokkaina ja selektiivisinä katalyytteinä ovat rajattomat. Nämä sovelluskohteet vaativat valmistusmenetelmiä jotka mahdollistavat nanopartikkelien koon ja kokojakauman tarkan hallinnan. Tämän työn tavoitteena oli kehittää luotettava menetelmä metallisten nanopartikkelien valmistamiseksi sähkökemiallisesti neste/neste-rajapinnalla. Kirjallisuusosassa käsitellään nanopartikkelien ominaisuuksia ja valmistusmenetelmiä sekä esitellään neste/neste-rajapintaan liittyvät peruskäsitteet. Lopuksi tarkastellaan diffuusion kontrolloiman nukleaatioreaktion teoreettista käsittelyä. Teoriaosassa tarkastellaan diffuusion kontrolloimaa nukleaatiota neste/neste-rajapinnalla sekä johdetaan nukleaatioreaktion ylipotentiaalin yhteys rajapinnan yli vaikuttavaan potentiaaliin. Kiinteille elektrodeille esitetty potentiostaattisen nukleaation teoria laajennetaan käsittelemään neste/neste-rajapinnalla tapahtuvaa nukleaatioreaktiota. Lisäksi johdetaan uusi teoria galvanostaattiselle tapaukselle. Kahta erilaista systeemiä kokeiltiin nanopartikkelien valmistamiseksi sähkökemiallisesti. Ensimmäisessä tutkittiin TOAAuCI_(4)(1,2-DCE):n ja K_(4)Fe(CN)_(6)(w):n välistä reaktiota. Systeemi havaittiin epäsopivaksi nanopartikkelien sähkökemialliseen valmistukseen. Toisessa systeemissä saostettiin palladiumpartikkeleita rajapinnalle. Ferroseenin (1,2-DCE) ja (NH_4)_(2)PdCI_(4)(w):n välinen spontaani reaktio vaikeutti nukleaatioreaktion sähkökemiallista tutkimista. Potentiaaliaskelien vasteena saadut virtatransientit osoittivat sähkökemialliselle nukleaatiolle tyypillisiä piirteitä. Uusi galvanostaattiselle tapaukselle johdettu teoria ennusti potentiaalitransientit erinomaisesti. Tulokset viittasivat lineaariseen virran ja partikkelien lukumäärän väliseen yhteyteen. Ferroseenin diffuusiokertoimelle saatiin arvo 1,1*10[-5] cm[2]/s sekä galvanostaattisista nukleaatiokokeista että mikroelektrodilla tehdystä syklisestä voltammetriasta

Influence of ligand structure on the stability andoxidation of copper nanoparticles

The stability and oxidation of copper nanoparticles stabilized with various ligands have been studied. Lauric acid-capped copper nanoparticles were prepared by a modified Brust–Schiffrin method. Then, ligand exchange with an excess of different capping agents was performed. Oxidation and stability were studied by UV–vis, XRD, and TEM. Alkanethiols and oleic acid were found to improve air stability. The oxidation resistance of thiol-capped copper nanoparticles was found to increase with the chain length of the thiol. However, excess thiol caused etching of the particles under nitrogen. With oleic acid no etching was observed under nitrogen. After oxidation, no traces of the ligand-exchanged particles were found, suggesting their dissolution due to excess ligand. Oleic acid protected the particles against oxidation better than the tested thiols at large excess (ligand–copper ratio 20:1).Peer reviewe

Electrodeposited Mesoporous Pt for Direct Ethanol Fuel Cells Anodes

In this study mesoporous Pt was electrodeposited from liquid crystal templates with different amount of Pt (0.60 mg/cm(2), 1.0 mg/cm(2) and 1.5 mg/cm(2)) directly on a carbon cloth using a potentiostatic method. These mesoporous Pt electrocatalysts were used as anodes for a direct ethanol fuel cell and the activity of ethanol oxidation reaction was studied. The electrochemical active surface area of the electrodes was measured using cyclic voltammetry under fuel cell conditions. Polarization and power curves for both commercial Pt and electrodeposited mesoporous Pt at different temperatures (30 degrees C, 50 degrees C and 70 degrees C) were studied, showing an increase of the performance with the temperature as expected. Despite lower Pt loading, all the mesoporous samples showed similar or better performances in the direct ethanol fuel cell when compared with the commercial Pt sample (4.0 mg/cm(2)). These results show that this catalyst preparation method can be a new route for the development of more efficient Pt based materials for direct alcohol fuel cells applications.Peer reviewe

Two-phase electrocatalysis by aqueous colloids

In this work, the combination of the advantages of two-phase catalysis, electrocatalysis and colloid catalysis is presented. It is shown that palladium or gold colloids prepared by citrate reduction can be charged negatively in a heterogeneous two-phase reaction and subsequently used as aqueous catalysts for dehalogenation reactions. This can be regarded as a new type of electrocatalysis. Keywords: ITIES, Catalysis, Two-phase catalysis, Colloid