Investigating Interfacial Structures of Nanomaterials and Their Photochemical and Photoelectrochemical Activities

The unique properties of nanomaterials arise from the nanoscale effects. For instance, the high surface area of nanocatalysts contributes to their enhanced catalytic activity, while the quantum confinement effect in quantum dots leads to the formation of discrete energy levels, granting them remarkable luminescent properties. These characteristics enable broad applications in various fields. In the nanoscale world, the structure of a material determines its functionality, making the study of the structure-property relationship fundamental to the design of nanomaterials. The first part of this thesis explores the modification of the catalyst’s interfacial structure to enhance photothermal catalysis performance. In chapter 2, widely used commercial Ruthenium catalysts on carbon substrate (Ru/C) were modified using surface ligands to alter their electronic structure. This resulted in a fourfold improvement in polyolefin hydrogenolysis efficiency while achieving the highest reported solid conversion efficiency for polyolefin hydrogenolysis to date. Similarly in chapter 3, TiO₂ photocatalysts were engineered with surface ligands to introduce photochromic properties, achieving a twelvefold increase in polyester glycolysis efficiency due to dynamic catalytic sites and localized thermal effects from expanded light absorption. The second part of the thesis investigate the relationship between nanomaterial interfacial structures and luminescence. In chapter 4, Nitrogen-doped carbon quantum dots displayed voltage-dependent emission color changes during Electrochemiluminescence (ECL), attributed to functional groups related surface states. Moreover, in chapter 5, graphene quantum dots exhibited competition between surface and aggregation state emissions in ECL. An analysis of their band structures revealed that the sp2-hybridized aromatic structure enhanced their quantum confinement effects. In chapter 6, sulfur quantum dots exhibited ultrabroad emission across 350–1050 nm through reaction enthalpy control. Synergistic analysis revealed the connection between their emission states and synthetic processes. Leveraging this understanding, zinc-doped silicon quantum dots were synthesized in chapter 7, demonstrating high triplet-state selectivity in chemiluminescence, with emission durations exceeding 100 hours and achieved the highest reported absolute chemiluminescence quantum efficiency based on quantum dots. In chapter 8, ECL experiments on ruthenium and palladium complexes showed that molecular symmetry and ligand coordination significantly influence emission wavelengths, laying the groundwork for designing precise nanomaterial structures with specific luminescent properties.