Thema der Dissertation:
Electron paramagnetic resonance spectroscopy for investigating metal-doped graphitic carbon nitride catalysts and detecting X-ray induced radiation damage.
Electron paramagnetic resonance spectroscopy for investigating metal-doped graphitic carbon nitride catalysts and detecting X-ray induced radiation damage.
Abstract: Rapid industrialization and population growth have resulted in rising energy demands and severe environmental challenges, including climate change from carbon dioxide emissions. Photocatalysis offers a promising strategy to address these issues by enabling carbon dioxide reduction and water splitting. Graphitic carbon nitride (gCN) has attracted attention as a photocatalyst due to its tunable properties, chemical stability and low cost. However, its efficiency remains limited by rapid charge recombination and narrow light absorption. Strategies such as supramolecular synthesis and transition metal doping can enhance performance, but the mechanisms behind these improvements require further study. This thesis employs electron paramagnetic resonance (EPR) and X-ray absorption spectroscopy (XAS) to investigate metal-doped gCN. While EPR provides insight into electronic structure and magnetic properties of the materials, XAS reveals oxidation states and coordination environments of metal dopants, including the EPR-silent species. A correlative approach would be highly valuable for investigation of catalytic mechanisms, but its development is limited by the size and complexity of conventional EPR spectrometers. Thefore, the first part of this work explores a compact EPR-on-a-Chip-based spectrometer with a portable electromagnet, designed for integration at synchrotron beamlines and provides an evaluation of its capability to detect X-ray-induced sample damage. The second part provides EPR and XAS investigation of gCN materials doped with copper, nickel, and iron. Based of the findings, a structural model of metal-doped gCN was proposed. It was suggested that metal ions, responsible for the narrower contribution to the EPR signal, may be positioned between different gCN flakes, while the ions, responsible for the broader contribution to the EPR signal, could be located in the pores between the tri-s-triazine units. The temperature-dependent behavior of the EPR signal was explained by the ferromagnetic nature of the species, potentially arising from a long-range exchange process mediated by conduction electrons delocalized within the π-conjugated structure of gCN. The EPR analysis of undoped gCN provided new insights into its degradation mechanisms, while the results on transition metal-doped gCN may be valuable for designing more efficient photocatalytic cells.
Time & Location
Oct 29, 2025 | 03:30 PM
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)