Customized ferroelectrics with optimized phase transition temperatures as highly active catalysts on the example of pyrocatalysis

• Applicant: Dr. Sascha Raufeisen
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550852162

The aim of the project is the development of customized ferroelectrics with optimized phase transition temperatures and thus high catalytic activity using the pyrocatalytic removal of micropollutants from water as an example application. Pyrocatalysis is a novel catalytic process that uses thermally excited pyroelectrics to initiate redox reactions, such as the generation of reactive oxygen species, H2 generation or CO2 conversion. The mechanism of catalyst excitation by thermal cycling has the unique potential to achieve high energy efficiency by recovering unused residual heat (e.g., industry) or by utilizing natural temperature gradients. First, however, the catalytic activity of the pyrocatalysts must be significantly increased. One of the most important material parameters for increasing this activity is the pyroelectric coefficient p. However, p is low for the most commonly used pyroelectric material BaTiO3. For this reason, customized ferroelectrics with optimized phase transition temperatures in the range of the operating temperature of wastewater treatment (< 30 °C) will be developed in this project. Suitable materials with these properties are, for example, Ba1-xSrxTiO3 (BST) or BZT-yBCT ((1-y)Ba(Ti0.8Zr0.2)O3-y(Ba0.7Ca0.3)TiO3) with special compositions regarding x and y (sol-gel or hydrothermal syntheses). Since p increases drastically near the phase transition temperature, these materials exhibit several times higher values for p compared to BaTiO3 and other pyrocatalysts. Due to further anomalies of certain properties in this area, these materials are also relevant for improving piezo- and photocatalysis. In addition to the composition of the catalyst materials to be developed, their particle size (adjustment of synthesis parameters; 6 - 50 nm) and oxygen vacancy concentration (e.g. vacuum annealing) are optimized. In preliminary work on BaTiO3, both parameters have also proven to be crucial parameters for greatly increasing pyrocatalytic activity. Since all three parameters can influence each other, fine-tuning of these parameters and a detailed material characterization are necessary. This allows to elucidate the structure-activity relationships underlying the activity enhancements. Particularly important is the determination of p, which for the first time allows a correlation between p and the pyrocatalytic activity. Overall, the aim is to increase catalytic activity by 1 to 2 orders of magnitude. The catalytic activity of the ferroelectrics will be estimated using the DCF redox assay (determination of the nonselective overall oxidation capacity) as well as the degradation of the endocrine-disrupting micropollutant Bisphenol A. Comprehensive catalyst characterization is based on BET, XRD, SEM/TEM, DSC, DRS, XPS, EPR, O2-TPD and pyroelectric measurements (Uni Bath).

• DFG Programme: WBP Position