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Cerium oxide particles as functional haloperoxidase mimics to combat biofouling

Subject Area Solid State and Surface Chemistry, Material Synthesis
Analytical Chemistry
Term from 2018 to 2023
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 405861793
 
Final Report Year 2024

Final Report Abstract

The aim of the study was to elucidate the antifouling mechanism of cerium oxide particles. Firstly, an LC-ESI-MS/MS method was developed for the quantitative determination of 34 quorum sensing (QS) molecules in order to record bacterial communication in natural waters and bacterial cultures. Subsequently, the mechanism of halogenation reactions was analysed in controlled lab experiments with a selection of representative QS molecules. In total, 46 reaction products were identified, which are formed by oxidation, hydrolysis and halogenation of different QS molecule groups (3-Oxo-Cn-AHL, alkyl-quinolones, pC-AHL and unsaturated AHLs). The developed LC-ESI-MS/MS method was also used for a mechanistic study in bacterial cultures. In these experiments, a brominated alkylquinolone was identified which is associated with QS. In the literature, this reaction product is discussed in connection with a reduction in bacterial growth, which could explain the antifouling effect of the cerium oxide particles. To increase the antifouling activity, different morphological cerium oxide particles were synthesised in order to get a better understanding of the underlying activity and thus to optimise the synthesis. It was observed that oxidative bromination reactions are particularly favoured by a high specific surface area, a strongly positive zeta potential, a high Lewis acidity and surface defects. These new findings make it possible to control the synthesis of highly active cerium oxide nanoparticles. The suitability of alternative metal oxides, which have a similar property like cerium oxide particles was investigated. In addition to bismuth-substituted particles (Ce1-xBixO2-d), lanthanide substitutions (Ce1-xLnxO2-x/2 (Ln = Pr, Tb) showed high catalytic activities. As a sufficient quantity of cerium oxide particles is required for antifouling coatings, different methods for scaling-up the synthesis of cerium oxide particles were developed. The synthesis of Ce1-xLnxO2-x/2 using ball mills was very promising. This energy-saving and residue-free method enables the production of larger quantities of cerium oxide nanoparticles and can also be transferred to an industrial scale. An alternative method is a continuous synthesis using high-throughput microfluidic benchtop systems. By reducing the reaction time and continuous operation, the system is highly scalable and can also be used in high-throughput syntheses for non-agglomerated cerium oxide particles with homogeneous size, morphology and crystallinity. Finally, composite materials based on cerium oxide have been developed with anti-fouling properties. A significant reduction in biofilm formation was demonstrated on a laboratory scale for various surfaces such as quartz glass or polyurethanes. In addition to the mechanism of the antifouling effect of cerium oxide particles, knowledge was also gained about the occurrence of unknown QS molecules for various bacterial species. This showed that bacteria communicate with a set of QS molecules, which means that QS can be relatively diverse. Therefore, in future mechanistic studies, we should not only focus on individual QS molecules, but always consider the entire range of QS molecules. Another finding, apart from the antifouling effect, is the possible influence of reactive halogen species on the QS system in disinfection.

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