It was the goal of this work to explore two different synthesis pathways using green chemistry. The first part of this thesis is focusing on the use of the urea-glass route towards single phase manganese nitride and manganese nitride/oxide nano-composites embedded in carbon, while the second part of the thesis is focusing on the use of the “saccharide route” (namely cellulose, sucrose, glucose and lignin) towards metal (Ni0), metal alloy (Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5, Cu0.5Ni0.5 and W0.15Ni0.85) and ternary carbide (Mn0.75Fe2.25C) nanoparticles embedded in carbon.
In the interest of battery application, MnN0.43 nanoparticles surrounded by a graphitic shell and embedded in carbon with a high surface area (79 m^2/g) were synthesized, following a previously set route.The comparison of the material characteristics before and after the discharge showed no remarkable difference in terms of composition and just slight differences in the morphological point of view, meaning the particles are stable but agglomerate. The graphitic shell is contributing to the resistance of the material and leads to a fine cyclic stability over 140 cycles of 230 mAh/g after the first charge/discharge and coulombic efficiencies close to 100%. Due to the low voltage towards Li/Li+ and the low polarization, it might be an attractive anode material for lithium ion batteries. However, the capacity is still noticeably lower than the theoretical value for MnN0.43. A mixture of MnN0.43 and MnO nanoparticles embedded in carbon (surface area 93 m^2/g) was able to improve the cyclic stability to over 160 cycles giving a capacity of 811 mAh/g, which is considerably higher than the capacity of the conventional material graphite (372 mAh/g). This nano-composite seems to agglomerate less during the process of discharge. Interestingly, although the capacity is much higher than of the single phase manganese nitride, the nano-composite seems to only contain MnN0.43 nanoparticles after the process of discharge with no oxide phase to be found.
Concerning catalysis application, different metal, metal alloy, and metal carbide nanoparticles were synthesized using the saccharide route. At first, systems that were already investigated before, being Pd0.9Ni0.1, Pd0.5Ni0.5, Fe0.5Ni0.5 and Mn0.75Fe2.25C using cellulose as the carbon source were prepared and tested in an alkylation reaction of toluene with benzylchloride. Unexpectedly, the metal alloys did not show any catalytic activity, but the ternary carbide Mn0.75Fe2.25C showed fine catalytic activity of 98% conversion after 9 hour reaction time (110 °C).
In a second step, the saccharide route was modified towards other carbon sources and carbon to metal ratios in order to improve the homogeneity of the samples and accessibility of the particle surfaces. The used carbon sources sucrose and glucose are similar in their basic structure of carbohydrates, but reducing the (polymeric) chain length. Indeed, the cellulose could be successfully replaced by sucrose and glucose. A lower carbon to metal ratio was found to influence the size, homogeneity and accessibility (as evidenced by TEM) of the samples. Since sucrose is an aliment, glucose is the better choice as a carbon source.
Using glucose, the synthesis of Cu0.5Ni0.5 and W0.15Ni0.85 nano-composites was also possible, although the later was never obtained as pure phase. These alloy nano-composites were tested, along with nickel0 nanoparticles also prepared with glucose and on their catalytic activity towards the reduction of phenylacetylene.
The results obtained let believe that any (poly) saccharide, including lignin, could be used as carbon source. The nickel0 nano-composites prepared with lignin as a carbon source were tested along with those prepared with cellulose and sucrose for their catalytic activity in the transfer hydrogenation of nitrobenzene (results compared with exposed nickel nanoparticles and nickel supported on carbon) leading to very promising results.
Based on the urea-glass route and the saccharide route, simple equipment and transition metals, it was possible to have a one-pot synthesize with scale-up possibilities towards new material that can be applied in catalysis and battery systems. / Im Rahmen dieser Arbeit wird sowohl die Synthese von Mangannitrid- und -oxid-Nanopartikeln, als auch die Synthese verschiedener Metall- und Legierungsnanopartikel untersucht. Einen Schwerpunkt stellt dabei die Optimierung der Synthese unter den Gesichtspunkten der Nachhaltigkeit dar, was sich insbesondere in der Verwendung diverser nachwachsender Rohstoffe als Kohlenstoffquelle äußert.
Für eine mögliche Anwendung in Akkumulatoren werden mit Graphit ummantelte MnN0.43-Nanopartikel mit einer großen Oberfläche (79 m^2/g) synthetisiert. Diese werden exemplarischen Ladezyklen unterzogen, wobei eine strukturelle und auch elektrochemische Stabilität festgestellt werden kann. Eine Mischung der Mangannitride mit Manganoxiden führt zu einer weiteren Verbesserung der Ladekapazität und einer weiteren Oberflächenvergrößerung (93 m^2/g). Die Langlebigkeit der Strukturen wird durch die Einbettung der Nanopartikel in Kohlenstoff unterstützt und kann zu einer Anwendung als Anodenmaterial in den heutzutage vielfach verwendeten Lithiumionen-Akkus führen.
Im Sinne der Nachhaltigkeit ist auch die Entwicklung von Katalysatoren. Dabei soll insbesondere die Verwendung von Lignin, was als Bestandteil vieler Pflanzen zwar leicht verfügbar, aber unglücklicherweise bisher chemisch unverwertbar ist, fokussiert werden. Um sich diesem Ziel zu nähern und entsprechende Mechanismen zur Reduktion des Lignins zu entwickeln, werden in dieser Arbeit zunächst verschiedene Kohlenstoffquellen (wie Cellulose, Sucrose und Glucose) zur Synthese von reduktiven Katalysatoren untersucht. Der Kohlenstoff dient dabei sowohl als preiswertes Reduktionsmittel für Metallsalze zur Gewinnung von Metallnanopartikel als auch zur Stabilisierung ebendieser. Es werden vielfältige Legierungen mit Nickel (z.B. Pd0.9Ni0.1, Pd0.5.Ni0.5, Fe0.5.Ni0.5, und Cu0.5.Ni0.5) aber auch ternäre Carbide (z.B. Mn0.75Fe2.25C) erhalten, die schon in ersten Alkylierungs- und Hydrierungsreaktionen ein großes Potential als Katalysatoren zeigen.
Um die erhaltenen Nanopartikel in zukünftigen Anwendungen nutzbar zu machen, ist eine ausführliche Charakterisierung unabdingbar. Auch die Ergebnisse der zahlreichen durchgeführten Analysen werden in dieser Arbeit zusammengestellt und bilden gemeinsam mit den optimierten Syntheserouten einen tiefgreifenden Überblick über dieses Forschungsfeld.
| Identifer | oai:union.ndltd.org:Potsdam/oai:kobv.de-opus-ubp:6983 |
| Date | January 2013 |
| Creators | Metzke, Sarah |
| Publisher | Universität Potsdam, Mathematisch-Naturwissenschaftliche Fakultät. Institut für Chemie |
| Source Sets | Potsdam University |
| Language | English |
| Detected Language | English |
| Type | Text.Thesis.Bachelor |
| Format | application/pdf |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/de/ |
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