Synthesis and application of CeO2 nanoparticles as catalyst for oxidative bromination

Abstract

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.