Energy-Efficient Chemical Production: Exploring Nonthermal and Thermal Processes in Plasmonic Catalysis

Abstract

The study of light-matter interactions has led to crucial developments in energy technology and chemical production. This work explores several fundamental applications of light-matter interactions and their underlying mechanisms, with a specific focus on plasmonic materials. Plasmon-enhanced chemical reactions have emerged as an energy-efficient alternative to conventional thermal catalysis. Plasmonic nanostructures exhibit localized surface plasmon resonance (LSPR), where surface-level free electrons participate in collective oscillations in response to external fields. Their eventual decay can lead to the formation of energetic charge carriers that can participate in redox chemistry directly (nonthermal contributions), or through scattering/recombination which produces a thermal response (photothermal contributions). While both processes can lead to improvements in reaction rates, it is difficult to deconvolute and quantify the contribution of each component. The central focus of this work is the use of the cover/uncover strategy to separate these two mechanisms in plasmonic ammonia synthesis. Chapter 1 lays the initial groundwork behind the concepts of catalysis, and expounds upon plasmonic theory and mechanisms. Chapter 2 then delves into an application of plasmonic catalysis in electrochemical ammonia oxidation, using bimetallic transition metal nitrides. The work reveals that while capable of demonstrating distinct fast and slow response currents, the exceptional photothermal properties of the catalyst severely limit the window of usable light intensities in non-aqueous ammonia oxidation environments. Chapter 3 shifts focus to solid-gas phase ammonia synthesis, where a molybdenum oxynitride based catalyst is used as a platform to demonstrate the cover/uncover strategy for deconvolution of plasmonic enhancement. The nonthermal plasmonic contribution is found to be extraordinary in this system, reaching up to 50% of the overall light enhancement. Chapter 4 studies the evolution of molybdenum oxide and the role of lattice nitrogen in ammonia synthesis. Over time, it was found that nitrogen from the produced ammonia can be incorporated into the molybdenum oxide lattice, resulting in significant rate enhancement. Given the unique properties of oxide, nitride, and oxynitride based systems in photothermal applications, Chapter 5 applies a machine learning-guided approach to screen for novel materials within this chemical class for solar applications, using the transfer matrix method to calculate solar weighted absorption (SWA). The models developed in this study displayed excellent capability to rank SWA and were used to predict SWA on a set of ~5000 materials from the Materials Project database. Finally, appendix A discusses the hydrogel-based extraction of critical minerals from waste streams that serve as useful components in catalysts and battery technologies. A fluorescent carbon dot-based on/off sensor was developed to screen for the presence of heavy metals such as cobalt, nickel, and manganese, and was integrated with nanocellulose-based hydrogels for stable and flexible sensing platforms.