Tailoring the Surface Chemistry of Aluminum Nanocrystals for Plasmon-mediated Catalysis
Halas, Naomi J.
Doctor of Philosophy
Light-driven chemical transformation with optically active plasmonic nanoparticles is a new paradigm in heterogeneous photocatalysis that may offer an ultimately sustainable alternative to traditional thermal-driven catalytic reactions. However, plasmonic metals nanostructures, despite strong coupling of their electron density with electromagnetic radiation, are not universally good catalytic materials, which limits the type of chemical reactions that can be induced directly on their surface. Recently, we introduced multicomponent plasmonic photocatalysts by rationally coupling of plasmonic nanoantennas directly to active catalytic reactors. This combination leverages and combines the light-harvesting abilities of plasmonic nanoparticles with high-efficiency catalysts to drive chemical reactions under milder operating conditions in contrast to traditional energy-intensive heat/pressure-driven chemical conversions. The modularity in ‘antenna-reactor’ design to create tailored catalysts holds promise to expand the scope and enhances the efficiencies of chemical reactions enabled by plasmonic photocatalysis. This thesis reports on utilizing aluminum nanocrystals (Al NCs), an earth-abundant metal with energetic and plasmonic properties, for developing novel light-activated photocatalysts, where chemically synthesized Al NCs were used as optical nanoantennas and the reactor was chosen among the semiconductor layer, active transition metal (TM) nanoparticles, and porous organic framework shells. Rational design and independent control over the catalytic and light-harvesting components in aluminum-cuprous oxide (Al-Cu2O) and aluminum-iridium (Al-Ir) ‘antenna-reactor’ nanoparticles results in light-driven mitigation of anthropogenic carbon dioxide and nitrous oxide, respectively. The mechanistic pathways of plasmonic photocatalysis for those reactions were investigated through the rigorous combination of the experimental and theoretical studies. Furthermore, the surface modification of Al NCs via bottom-up encapsulation within metal-organic frameworks (MOFs) shell layer was investigated. MOF growth around Al NCs provides a new level of controlling the growth and surface chemistry and plasmonic characteristics of Al NCs. The enhanced reactant uptake near the plasmonic center afforded by the porous nature of MOF shell results in increased photocatalytic activity of Al NCs, which is observed for the hydrogen-deuterium exchange and reverse water-gas shift reactions. The transition from noble metals to aluminum-based antenna-reactor heterostructures in plasmonic photocatalysis provides a sustainable route to high-value chemicals and reaffirms the practical potential of plasmon-mediated chemical transformations.
Aluminum nanocrystals; Plasmonic photocatalysis; Antenna-reactor; Metal-organics frameworks