Synthesis, surface chemistry, and application of fully inorganic gold nanoclusters by pulsed laser fragmentation in liquids

In his 1857 lecture, Michael Faraday featured the fascination of the relations of gold with light. His passion is served to the full extent within this thesis as the interaction decisively determines the synthesis and characteristics of colloidal inorganic gold nanocluster Gold nanoclusters with diameters < 2 nm are known for their fluorescent behavior with quantum yields several orders of magnitude higher than bulk gold, making them interesting candidates for e.g., optical sensing and applications in the field of catalysis. The origin of the fluorescence of noble metal nanoclusters is a controversial topic addressed in many studies but could not been clarified to date. The primary drawback is that current state-of-the-art chemical synthesis methods only give access to ligandcapped systems. Hence, core emission and ligand-to-metal-surface charge-transfer contributions cannot be differentiated. To solve this conundrum and to fundamentally understand the origin of the gold nanoclusters fluorescence, a new class of nanomaterials, fully inorganic ligand-free colloidal nanoclusters, is required. In this thesis, the size-controlled generation of ligand-free gold nanoclusters with defined surface charge chemistry by a modern laser fragmentation in liquids technique is developed and optimized. This includes experimental series including advanced in-situ methods, linking physical and chemical process parameters to size distribution, yield, and surface chemistry of the fully inorganic gold nanoclusters, with interesting implications on surface oxidation and surface charge. Furthermore, it is discovered that inorganic gold nanoclusters possess pronounced photoluminescence affected by transition states from the core and inorganic surface states controlled by the ionic nanoenvironment. The study is complemented by experiments demonstrating the impact of core composition on photoluminescence by utilization of AuPt alloy series and scouting experiments on the impact of thiolated and non-thiolated surface ligands on photoluminescence. Finally, the applicability of the generated fully inorganic gold nanoclusters in oxidation catalysis is demonstrated in three independent model reactions. Overall, fully inorganic ligand-free gold nanoclusters are exploited. The whole process chain from their optimized synthesis and in-depth characterization to applications in catalysis is demonstrated. The emphasis of this work is on their optical properties, which can help to shed light on the highly disputed origin of fluorescence in metal nanoclusters.