The capture of hot electrons at the nanoparticle-molecule interface
Creators: name: Harrell, Jaren
Publisher: name: No Publisher Supplied
Year: 2023

description: Hot electron transfer from photoexciting nanoparticles is an important mechanism that occurs at the nanoparticle-semiconductor and nanoparticle-molecule interface. Less is known about the latter, and having a fundamental understanding of the electron transfer dynamics along with the dynamics of hot electron generation is the key to efficient photochemical reactions that are especially important for photocatalysts. Previous theoretical studies produced calculations to determine the hot carrier energy distribution and decay times for each of the nonradiative events that transpire to dissipate the absorbed photon energy; all these events occur at the sub-picosecond timescale and are not well separated. Ultrafast spectroscopy experiments cannot measure the specific energies of the hot carriers or unravel the exact mechanism. However, we can monitor the differences and evolution of an electron-accepting molecule’s transient absorption spectra. It will provide information about electron transfer and recombination dynamics. Methyl viologen is a well-known electron acceptor and has a prominent absorption band when reduced from its MV2+ redox state to its radical cation (MV+·). We perform ultrafast spectroscopy experiments by photoexciting silver and gold nanoparticles with viologen moieties that are able to functionalize the nanoparticles’ surface. We monitor the change in the transient absorption spectra of viologen capturing hot electrons and calculate its efficiency. The lifetime of the functionalized 10 nm silver and 15 nm gold were longer than that of the bare nanoparticles. In contrast, the 30 nm silver and gold nanoparticles exhibited faster decay times. The efficiency of hot electron capture is influenced by the nanoparticle size, composition, excitation power, and nanoparticle-molecule interfacial distance. Analyzing these parameters will help in elucidating the electron transfer dynamics at the interface. The electron capture efficiency ranged from 8% to 11% for functionalized 10 nm silver nanoparticles and ~5% for 30 nm silver nanoparticles. The functionalized gold nanoparticles exhibited changes in their transient absorption spectra and decay profiles in which the most probable explanation was due to viologen capturing hot electrons. Our findings show that functionalized silver and gold nanoparticles with viologen moieties were able to capture hot electrons from photoexcited nanoparticles. The fundamental understanding of the electron transfer dynamics at the nanoparticle-molecule interface has meaningful implications for increasing the electron transfer efficiency in photochemical reactions. Chapter 2 SummaryThis work was done under my previous advisor, who parted ways before I was able to complete all the studies. Materials that contain amidoxime functional groups have been developed to be deployed for mass-scale uptake of uranium from seawater. The primary use of the amidoxime functional group is sequestering uranium from seawater due to its high selectivity towards uranium. However, there are potential applications to deploy amidoxime functionalized materials to remove heavy metals for water purification as there is an affinity to these metals along with uranium. In this chapter, a cyclic monomer containing sulfur was synthesized with a nitrile pendent group which is converted to the amidoxime functional group. These sequestering polymers were the first to be polymerized by ring-opening metathesis polymerization. Typical amidoxime sequestering polymers and materials are synthesized by way of radical polymerization. The polymers were then treated to convert the nitrile group to an amidoxime and used to conduct binding studies in simulated seawater containing uranium. The was as much as 49% binding with the polymer in seawater.If the polymer was to be used for industrial purposes is typically done using solid-state materials, such as resins. It was shown that the synthesized monomer was able to be polymerized off the Merrifield resin.