Light-Driven Multielectron Chemical Transformations with Tailored Nanoparticles

Abstract

Nature has always been the underlying inspiration for various solar energy conversion technologies and among them, solar-to-chemical energy conversion in photosynthesis is considered to be the most elegant way to make molecules. Consequently, the area of photocatalysis is at the forefront of modern research. At the core of all photocatalytic transformations are the three fundamental steps: generation of charge carriers, separation, and charge transfer/utilization. Based on these fundamental steps, our choice of photocatalysts is plasmonic metal nanoparticles (NPs) and quantum dots (QDs), alongside their unique optoelectronic properties and rich surface chemistry. The main focus of this thesis is to maximize the efficiency of each fundamental step through the rational design of both the core as well as the surface of the chosen photocatalysts for challenging multielectron chemical transformations. We started off by understanding the prerequisite light excitation attributes in plasmonic photocatalysis for the regeneration of nicotinamide cofactors with gold nanorods (AuNRs). This work emphasizes the need for an appropriately chosen catalyst–reactant system and reaction conditions to gain meaningful insights into various factors controlling the product yield and selectivity in plasmonic photocatalysis. Next, with the aim of synthesizing important commodity chemicals such as ammonia, we fine-tuned the photocatalyst design to arrive at indium phosphide (InP) QDs with appropriate surface chemistry to drive selective nitrate-to-ammonia conversion. Detailed mechanistic investigations helped us gain an in-depth understanding of the important pathways involved. In the final work, the efficiency of charge extraction was enhanced by the appropriate choice of inorganic-surface ligands on the InP QDs for light-driven ammonia synthesis. In summary, our work showcases the need for appropriate design core and surface ligands to maximize each fundamental step in photocatalysis for challenging multielectron transformations. The concepts developed in this thesis can be easily extended to complex molecule/material synthesis in a sustainable manner, including multicomponent reactions.