Two-Dimensional Molybdenum Disulfide for Sunlight Harvesting: Photophysical and Catalytic Insights

The increasing demand for energy, together with growing concerns about climate change and environmental degradation, has forced a global shift towards renewable energy sources. Sunlight, as a non-polluting and infinitely renewable source of clean energy, has gained significant attention in this transition. Tremendous efforts have been devoted to exploring suitable materials for harvesting sunlight, aiming to address the energy and environmental challenges we face today. Among the materials investigated, two-dimensional molybdenum disulfide (MoS2) has emerged as a promising candidate for sunlight harvesting applications. Its unique photophysical and catalytic properties make it particularly attractive for solar energy conversion. This thesis focuses on investigating the photophysical behavior and catalytic capabilities of MoS2 nanosheets, offering insights into its potential for advancing solar energy utilization. The thesis begins by exploring the role of Ag nanoparticle cocatalysts in improving the photocatalytic properties of MoS2 nanosheets, elucidating the mechanisms underlying photoinduced charge separation. Subsequent chapters investigate the storage of electrons in MoS2 nanosheets induced by sunlight excitation and externally applied bias, establishing its potential for energy storage. Additionally, the corresponding changes in optical and electrical properties driven by the weakening of interlayer van der Waals interactions and the introduction of free charge carriers into MoS2 nanosheets are discussed. Spectroelectrochemistry is employed to further probe the mechanism underlying the stabilization of stored electrons via counter cation intercalation. The analysis of how different cation sizes affect MoS2 intercalation offers viewpoints for optimizing the design and application of MoS2 nanosheets for advanced solar energy conversion technologies. Furthermore, the thesis examines the dissociative adsorption of water on sulfur vacancy-rich MoS2 interfaces using in-situ near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The findings highlight the potential of surface-engineering techniques to improve the catalytic performance of MoS2, rendering it a more efficient material for water dissociation reactions. Overall, this thesis discusses the photophysical properties and surface chemistry of molybdenum disulfide. These findings provide perspectives for the utilization of MoS2 in sunlight harvesting applications and beyond, offering solutions for addressing the energy and environmental challenges of the future.