SILVER HALIDE NANOCUBES: UNIQUE PLATFORM FOR DEVELOPING HIGH-PERFORMANCE CATALYSTS

Abstract

Controlled synthesis of functional nanostructures is of paramount interest due to their novel properties and efficient functionalities. The size and morphology of each particle in the nanoscale contribute to their optical and electronic properties. Also, the collective arrangement of these nanostructures in 3D space maximizes active sites available for the cost-effective catalysis. Recent advances in the field show a vast range of nanostructures with unique designs that affect their catalytic properties. In this dissertation, utilizing silver halides as a unique platform to develop high-performance catalysts were discussed with their respective synthesis strategies, structural evolution, and structure-related properties. Initially, we synthesized well-defined silver chlorobromide (AgCl0.5Br0.5) nanostructures investigating the effects of various reaction parameters on the synthesis. Simple reaction parameters were overlooked to gain additional controllability on determining the morphology of the nanocrystals regardless of the composition. Thus, the influence of the size and exposed surface facets was investigated towards photocatalytic activity performing methylene blue degradation on AgCl0.5Br0.5 with different sizes and morphologies, under visible light. Then, the ability to use these AgCl0.5Br0.5 nanocubes were investigated as a reactive and sacrificial template for the synthesis of nanoplates and nanoshells. As an example, fast precipitation reaction between Ag+ and benzenethiol (BT–) results in an uncontrollable growth leading to aggregated structures. The low solubility and the planer surfaces of the silver halide cubes were utilized to reduce the reaction rate and promote the growth of layered AgBT as plates, which can be organized into hollow nanostructures. Time-dependent microscopic and spectroscopic measurements showed the structural evolution and associated kinetics of the conversions. Developing a comprehensive understanding enabled generalizing the procedure to synthesize other silver-based hollow nanostructures. Mechanistic studies showed two different hollowing mechanisms involving, that depends on the anion being exchanged. The degree of nucleation and the crystal structure of silver-sulfur compounds determined the relative diffusion of ions leading to their overall size and morphology. The hollow morphology was shown to have higher stability with a large surface area relative to its aggregated solid counterpart. Next, highly porous Ag nanostructures were synthesized electrochemically, using silver thiolate nanocages. High porosity and their arrangement as plates enhanced available active sites and mass transport for CO2 electroreduction. Furthermore, the strategy was extended to design bimetallic nanostructures with enhanced bimetallic boundaries where selectivity of ethanol formation from CO2 electroreduction can be increased. Overall, the study explores the novel approaches to utilize chemical and physical properties of silver halides for various material designs that determines their enhanced performance.