PhD Oral Exam - Nazli Jodaeeasl, Physics

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

Understanding and controlling surface–adsorbate interactions is crucial for designing advanced materials for applications such as toxic gas capture, sensing, and electronics. Although metal-organic frameworks (MOFs) are promising nanomaterial sorbents for toxic gases, the relationship between their structural and electronic properties and adsorption performance has not been established, limiting their rational design. Similarly, a detailed understanding of surface reactivity is lacking for other nanomaterials, such as silicene. Recent experiments show that silicene synthesized on highly oriented pyrolytic graphite (HOPG) exhibits stability against oxidation after weeks of air exposure, in contrast to previous results on other substrates and theoretical predictions. This discrepancy highlights the need for computational investigations to clarify surface reactivity and substrate effects. In this study, spin-polarized density functional theory (DFT) with Hubbard U correction is employed to investigate the adsorption mechanisms of toxic molecules on MOFs, focusing on M-MOF-74 (M = Mg, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and water-stable frameworks such as UiO-66, UiO-66-NH₂, UiO-67, MIL-53 and MFM-300. Toxic molecules adsorb on M-MOF-74 at unsaturated metals, whereas water-stable MOFs exhibit weak physisorption through hydrogen bonding. Including the Hubbard U correction is essential for accurately modeling the electronic structures and binding energies of MOFs containing transition metals. The M-MOF-74s display diverse magnetic behaviors. Interestingly, magnetic configurations do not significantly affect binding energies, suggesting that DFT calculations without considering magnetic states can reliably predict adsorption energies for these MOFs. However, cases such as V-MOF-74 show potential for magnetic sensing of NO₂. Furthermore, functionalization of MOFs, such as UiO-66-NH₂, enhances adsorption of NH₃, NO₂, and SO₂, highlighting the role of linker modifications in improving adsorption performance. As for silicene, DFT calculations using the generalized gradient approximation (GGA) indicate that both free-standing silicene and silicene on HOPG interact and react with O2 via a barrierless process. However, DFT with hybrid functional reveals small energy barriers for oxidation, and Hartree–Fock methods predict significantly larger barriers, underscoring the sensitivity of predicted oxidation pathways to the choice of computational method. This study demonstrates the importance of advanced computational approaches and material design strategies in understanding the surface reactivity of materials.