Synthesis And Application Of Ceo2 Nanoparticles As Catalyst For Oxidative Bromination
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Synthesis and Application of CeO2 Nanoparticles as Catalyst for Oxidative Bromination
In recent years, the so-called "nanozymes" have come to the forefront of research. These are nanomaterials that have the property of mimicking enzymes. In this dissertation, ceria nanoparticles are presented as such an enzyme mimic. Cerium oxide can mimic the enzyme vanadium bromoperoxidase in the presence of bromide and hydrogen peroxide by oxidative bromination. In this work, various syntheses of ceria nanoparticles and their potential applications are discussed. In addition, oxidative bromination with CeO2 as catalyst and the factors that promote it are examined in more detail. In the first chapter, it was investigated if doping with the lanthanides praseodymium and terbium can increase the catalytic activity of the ceria nanoparticles. For this purpose, a mechanochemical synthesis was established in a planetary ball mill by a simple metathesis reaction. Thereby the catalytic activity could be increased almost twofold by doping and was found to be dependent on various factors such as zeta-potential and specific BET surface area. Likewise, Raman and ESR spectroscopy demonstrated that the incorporation of the trivalent cation creates oxygen vacancies, which also have an important effect on the catalysis rate. Another project consisted of analyzing different morphologies of ceria nanoparticles for their catalytic activity. For this purpose, oxidative bromination was carried out and evaluated based on the bromination of thymol using NMR spectroscopy. This showed a clear difference between the different morphologies with respect to catalytic activity. Here, as well, it was demonstrated that influences such as zeta potential and specific BET surface area have an important effect on catalysis. In addition, Raman spectroscopy showed that the ceria nanoparticles with the different morphologies degraded the substrate hydrogen peroxide after a short time on the particle surface, which significantly slowed down the catalysis. Furthermore, as an application, polycarbonate plates were coated with functionalized CeO2 nanoparticles. For better adhesion of the particles, a polar surface was created with the help of oxygen plasma. A homogeneous coating of functionalized ceria nanoparticles was used to create a nanozyme. The task of the nanozyme is to brominate signal molecules of bacteria using oxidative halogenation to inhibit biofilm growth. As a result, the altered signal molecules are no longer recognized by the bacteria, the communication is interrupted, and the biofilm growth is stops. Subsequent bioassays with the Gram-negative bacterium Pseudomonas aeruginosa showed an inhibition of 75% of the biofilm growth after polycarbonate coating with CeO2 nanoparticles in contrast to pristine polycarbonate plates.
Aqueous-phase Catalytic Conversions of Renewable Feedstocks for Sustainable Biorefineries
Author: Georgios Papadogianakis
language: en
Publisher: Frontiers Media SA
Release Date: 2024-08-23
Today, there is growing interest in aqueous-phase catalytic conversions for the valorization of renewable biomass-based feedstocks for biorefineries to produce, in a sustainable way, biofuels, chemicals, power, energy, materials, pharmaceuticals and food. This is because of the highly polar nature of water which makes it an ideal medium to convert polar biomass-based lignocellulose (cellulose, hemicellulose, lignin), with high oxygen content, and their upgraded products such as hydrophilic carbohydrates, platform chemicals and their derivatives. Another reason which makes water the solvent of choice is that water itself is involved either as a reagent or as a byproduct even in large amounts in typical conversions for the valorization of biomass. The obtained intermediates further react in the aqueous medium, often without any separation and purification, to manufacture more valuable products. This results in substantial energy savings, lower emissions and economic benefits. Furthermore, water could act as a catalyst in conversions of biomass-based feedstocks such as in liquefaction reactions under subcritical conditions. Moreover, novel types of catalytic reactivity have been observed in the aqueous solvent, not only with water-soluble transition metal catalytic complexes, but also with conventional heterogeneous catalysts and catalytic nanoparticles in a broad spectrum of different reactions such as, inter alia, aldol condensations and hydrogenation reactions. For example, in the aqueous-phase hydrogenation of the biomass-based key platform chemical levulinic acid into γ-valerolactone and beyond, employing heterogeneous catalysts and nanoparticles the presence of water has a beneficial effect and accelerates the reaction rates, whereas in organic solvents much lower activities were observed. This promotional effect of water in the hydrogenation of levulinic acid was proved by many experimental and theoretical studies using a broad spectrum of different types of catalytic systems.
Nanozymology
This book introduces the new concept of “nanozyme”, which refers to nanomaterials with intrinsic enzymatic activity, rather than nanomaterials with biological enzymes incorporated on the surface. The book presents the cutting-edge advances in nanozyme, with emphasis on state-of-the-art applications in many important fields, such as in the biomedical fields and for environmental protection. The nanozyme is a totally new type of artificial enzyme and exhibits huge advantages over natural enzymes, including greater stability, low cost, versatility, simplicity, and suitability for industry. It is of interest to university researchers, R&D engineers, as well as graduate students in nanoscience and technology, and biology wishing to learn the core principles, methods, and the corresponding applications of “nanozyme”.