Authors:	Spetter, Dmitri
Title:	Nanostructured transition metal oxides and sulfides for catalytical and energy applications
Online publication date:	18-Oct-2022
Year of first publication:	2022
Language:	english
Abstract:	The aim of this work was the development of novel compounds for application in energy engineering and catalytic processes. The focus was placed on oxides and sulfides of molybdenum, tungsten and iron. In addition, it was important to establish a synthetic pathway, which is potentially easily scalable. The first part ofthe work deals with the production of tungsten-molybdenum oxides (TMOs) by means of two different synthetic routes, but starting from the same precursor compounds. Thus, by a simple precipitation technique, nanoflakes of TMO were prepared at room temperature in almost quantitative yield. The elemental composition and morphology of the compounds can be easily controlled without the addition of a surfactant. Tue TMO nanoflakes are suitable for use in photocatalysis due to their strong absorbance of visible light. Ifthe same reaction was carried out under solvothermal conditions in the autoclave, microspheres of mixed TM Os were obtained. These novel particles were examined for their use in two major technical fields. lt was found that the mixed oxides yield significantly better results as catalyst materials in water splitting reactions than the pure oxides of tungsten or molybdenum. Thus, a synergetic effect could be demonstrated, which was proposed by other publications for affecting the physico-chemical characteristics of the mixed compounds. Photoelectrocatalysts such as the developed TMO microspheres are elementary components of fuel cells, which are an immensely important alternative for future energy production besides fossil fuels. Furthermore, the use of the same microspheres as catalysts in the oxidation of sulfides was investigated. This reaction is an important step on the route to many organic substrates, e.g. the preparation of active ingredients. The sulfoxidation was carried out in aqueous medium with hydrogen peroxide as oxidant, thus establishing a green chemistry set-up. Due to its chemical properties, this reagent is superior to other oxidizing agents in terms of toxicological and environmental properties. In the reaction of the TMO catalysts with various sulfides in the presence of hydrogen peroxide, significantly faster reactions than previously known to the corresponding sulfoxide or sulfone were achieved. In the second part, a new synthesis of porous iron oxide particles was investigated. Starting from templates of mesoporous silica, iron oxide particles with a cellular structure were obtained by nucleation and growth on the silica particles. However, it was not possible to synthesize pure mesoporous hematite nanoparticles since a residual amount of silicon remained in the product. The investigation of these particles in the decomposition of Rhodamine B also showed that the mesoporous silica particles (remaining from the synthesis) strongly delayed the oxidative reaction. However, the product itself showed significantly higher conversion rates than in the absence of a catalyst. Thus, the use of the silica-hematite particles in the field of wastewater treatment for the removal of dyes is essentially possible. In the final part, various nanoparticulate compounds of tungsten and molybdenum sulfide were tested as friction-reducing additives in synthetic oil. Tue production of the particles was carried out partly using a novel wet-chemistry approach in benzyl alcohol, in which nanoflakes of molybdenum oxysulfide were obtained. In friction experiments, a significant reduction of both the friction coefficient and the wear on the components was found, especially for this product. To date, the pure sulfide materials have been regarded as the best additive, which is why the results of the oxysulfide offer a new approach for the development of better lubricant additives.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-6870
URN:	urn:nbn:de:hebis:77-openscience-cbaaf43d-23af-4040-9be0-43ef19eb6c748
Version:	Original work
Publication type:	Dissertation
License:	CC BY-ND
Information on rights of use:	https://creativecommons.org/licenses/by-nd/4.0/
Extent:	206 Seiten, Illustrationen, Diagramme
Appears in collections:	JGU-Publikationen