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In this study, we investigated electric explosion of iron wire in distilled water with different energy input adjusted by charging voltage. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), showing the presence of iron and multiple iron-based compounds oxides with contents influenced by the experimental conditions. In particular, pure FeO(OH) nanoparticles were obtained using electric explosion of iron wire with energy input of 1125 J at charging voltage of 15 kV. Analysis of discharge current and resistive voltage data indicate that the high energy input induced by strong plasma discharge at high charging voltage is a key factor to form FeO(OH). This study presents a one-step method to synthesize FeO(OH) nanoparticles using electric explosion of iron wire.

1\. Introduction 2\. Methods and Experimental Setup 3\. FeO - An Ultrathin Metal Oxide Film in Ambient Conditions 4\. CO Oxidation on MgO at Ambient Pressure 5\. Deposition of Pd on MgO/Ag(001) by Wet Impregnation 6\. Conclusions A. Two Dimensional Silica on Ru(0001) Bibliography, Surface science model catalysts are elementary representations of applied systems by which different parameters of a catalytic process can be investigated separately and at the molecular scale. Studies on such model systems constitute the basis for present studies which aim at bridging the materials and pressure gap towards applied catalysts systematically. In this framework, the present thesis contributes to this goal by applying two approaches towards more realistic catalyst models. The first part of this work documents research on ultrathin, metal supported oxide films in ambient conditions. FeO(111)/Pt(111) films were exposed to air and water and tested regarding CO oxidation at ambient pressure by infrared reflection absorption spectroscopy (IRAS). Pre - and post characterization was performed by low energy electron diffraction (LEED), temperature programmed desorption (TPD) and X- ray photoelectron spectroscopy (XPS). Experimental and theoretical results suggest, that in the presence of oxygen and water, a bilayer (FeO)!trilayer (FeO(OH)) transition occurs. The resulting FeO(OH) trilayer is stable in ambient conditions and shows similar CO oxidation activity at ambient pressure as previously reported for FeO2. Ultrahin MgO(001) films grown on Ag(001) and Mo(001) were likewise tested for CO oxidation activity at 1 bar total pressure and characterized by XPS. Theoretical and ultrahigh vacuum (UHV) studies had indicated that these systems might efficiently activate molecular oxygen. However, no catalytic activity for ultrathin MgO(001) films in ambient conditions was observed. The second part of this work presents an approach which takes into account the fact that most applied heterogeneous catalysts are prepared by wet chemical methods. Here, a Pd catalyst was prepared by liquid phase deposition (LPD) from a PdCl2 precursor solution onto a MgO(001)/Ag(001) model support. Dissolution experiments, where the samples were post - characterized by AES (Auger electron spectroscopy), showed that MgO/Ag(001) films are only long - term stable in alkaline solutions. The XPS data indicates a linear correlation between Pd loading and precursor concentration. XPS was also used to characterize the thermally induced precursor decomposition at relevant stages. The activated LPD catalysts showed similar CO adsorption properties and activity towards CO oxidation as corresponding catalysts prepared by PVD (physical vapor deposition) \- which is evidenced by TPD measurements., Surface Science Modellkatalysatoren sind stark vereinfachte Ausführungen angewandter Katalysatoren. Sie ermöglichen es, verschiedene Parameter eines katalytischen Prozesses getrennt voneinander und auf molekularer Ebene zu untersuchen. Bisherige Studien solcher Modellsysteme stellen die Grundlage dar für die heutige Forschung, die bestrebt ist, existierende Diskrepanzen der Druckbereiche (pressure gap) sowie der Material - und Strukturkomplexität (material gap) zwischen Modellen und angewandten Systemen systematisch zu verringern. Der erste Teil der vorliegenden Arbeit dokumentiert Untersuchungen von ultradünnen, metallgeträgerten Oxidfilmen unter Umgebungsbedingungen. FeO(111)/Pt(111) Filme wurden Luft und Wasser ausgesetzt und bezüglich ihrer katalytischen Aktivität hinsichtlich der Oxidation von CO unter Umgebungsdruck mittels Infrarot -Reflexions - Absorptionsspektroskopie (IRAS) getestet. Die Prä - und Postcharakterisierung wurde anhand von niederenergetischer Elektronenbeugung (LEED), temperaturprogrammierter Desorption (TPD) und Röntgenphotoelektronenspektroskopie (XPS) durchgeführt. Experimentelle und theoretische Ergebnisse deuten darauf hin, dass in Gegenwart von Sauerstoff und Wasser ein Übergang vom zweilagigen FeO zu einem dreilagigen FeO(OH) Film stattfindet. Die FeO(OH) Dreilage ist stabil unter Umgebungsbedingungen und besitzt eine ähnliche katalytische Aktivität gegenüber der Oxidation von CO unter Umgebungsdruck wie FeO2. Ultradünne MgO Filme auf Ag(001) und Mo(001) wurden ebenfalls auf katalytische Aktivität bezüglich der CO Oxidation unter Umgebungsdruck untersucht und mittels XPS charakterisiert. Theoretische Studien und Experimente im UHV hatten darauf hingedeutet, dass diese Systeme in der Lage sind, molekularen Sauerstoff zu aktivieren. Es wurde jedoch keine katalytische Aktivität ultradünner MgO Filme unter Umgebungsbedingungen beobachtet. Der zweite Teil dieser Dissertation zeigt einen Ansatz auf, welcher der Tatsache Rechnung trägt, dass die Mehrheit der angewandten heterogenen Katalysatoren mit Hilfe nass - chemischer Methoden hergestellt wird. In dieser Arbeit wurde ein Pd Katalysator durch Flüssigphasenabscheidung (LPD) aus einer PdCl2 Präkursorenlösung auf einem MgO/Ag(001) Modellsubstrat abgeschieden. Auflösungsexperimente, bei denen die Proben durch Auger Elektronenspektroskopie (AES) post - charakterisiert wurden, zeigten, dass dünne MgO/Ag(001) nur in alkalischen Lösungen über einen längeren Zeitraum stabil sind. Die XPS Daten weisen auf eine lineare Korrelation zwischen der Pd Konzentration in der Lösung und der Menge an abgeschiedenem Pd hin. Die schrittweise thermische Zersetzung der Pd - Präkursoren wurde mit XPS untersucht. TPD Messungen zeigten, dass der aktivierte Pd -LPD Katalysator sich durch ähnliche CODesorptionseigenschaften und Aktivität gegenüber der Oxidation von CO auszeichnete wie ein entsprechender Pd Katalysator, der mittels PVD (physikalische Gasphasenabscheidung) hergestellt wurde.

Biological electrochemical systems, as Microbial electrolysis cells (MEC) or Microbial fuel cells (MFC), use electroactive biofilms in which bacteria have the ability to transfer electrons to an external acceptor. Previous studies have shown difficulties with reproducing the composition of electroactive biofilm microbial communities and also to obtain repeatable performance from a natural inoculum as marine sediments. Electroactivity of bacteria involving their ability to exchange electrons with an external electron acceptor (the electrode), the enrichment method adopted in this study had been chosen to select microorganisms which can reduce iron oxides. Sediments from a salt Plant had been enriched in a medium which contains Fe(III) in which bacteria reduce Fe(III) to form Fe(II). This enriched community had been used to inoculate reactor to form an electroactive biofilm. This process had been reiterated several times to observe the effect of enrichment culture stages on bioelectrochemical process and electroactive biofilm communities. As experimental design, a three-electrode system was used in which the graphite working electrode potential was fixed with a potentiostat (Biologic VSP) according to a reference electrode (SCE). The current produced between the working electrode and an auxiliary electrode was monitored. A voltage of 0.2 V vs SCE was applied to the anode with acetate as carbon source in synthetic seawater, at pH 7 and 37°C. At least, an increase of coulombic efficiency from 15.19±1.91 % to 49.52±3.77% had been obtained. The final biofilm had been collected and microbial diversity is under characterization by 16S and HydA DNA- fingerprinting methods.