1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]Tf2N) was investigated as a multifunctional solvent, ligand, and reducing agent for platinum deposition onto well-defined CdSe@CdS nanorods. Platinum deposition was carried out thermally and photochemically using Pt(acac)2 as the metal precursor. Thermal deposition was investigated in [BMIM]Tf2N with and without addition of a sacrificial reducing agent, and product topology was compared with the products obtained from polyol reduction using 1,2-hexadecanediol, oleic acid, and oleylamine in diphenyl ether. Photochemically induced platinum deposition was carried out at room temperature in [BMIM]Tf2N, and product topology was compared with the photodeposition products obtained from a toluene dispersion. Thermal deposition of platinum in ionic liquid showed rods of broken morphology and small platinum nanoparticles speckled across the rods’ surface, while photodeposition of platinum exhibited particles decorated throughout the nanorod surface but larger in size than those exhibited by thermal means. Photocatalytic reduction of methylene blue was studied using these Pt-CdSe@CdS heterostructured nanoparticles, and catalytic performance was correlated with topology and synthetic history. Initial findings of catalytic performance suggest that there in an advantage of depositing platinum nanoparticles onto the CdSe@CdS in the ionic liquid system. Methylene blue dye was degraded using each system and the results show and there is an increased performance of the nanorods synthesized in the ionic system.

The development of nanoscale heterostructure photocatalysts for the effective, direct utilization of visible light (400-750 nm, ~44% of solar spectrum) to drive important chemical conversions is a prime research area in the field of photocatalysis. Particles at nanoscale dimensions have a large surface area-to-volume ratio, expose a high number of active surface sites, and exhibit unique electronic properties (different from bulk) that are beneficial for improving the overall catalytic activity. However, the advantages of size reduction are often overshadowed by the low optical absorption (as absorption power  size3) and colloidal instability (extensive aggregation) of particles at the nanoscale. In this dissertation, we demonstrate a strategy to improve the colloidal stability and enhance the optical absorption of nano-sized semiconductor and metal nanoparticles (NPs) that exhibit weak visible light absorption. The colloidal, free-standing NPs are placed on transparent, dielectric silica nanospheres (SiOx NSs) that act as optical antenna supports, forming SiOx/NP composite nanostructures. The spherical morphology of SiOx enables scattering resonances (Fabry Perot or Whispering Gallery Modes) which enhances the local electric field on or near the surface of the NS. The NPs placed on the surface of SiOx NS interact with the locally enhanced electric field and exhibit improved optical absorption. By varying the size of the SiOx NS, the resonance wavelengths and the intensity of the local electric field enhancement can be tuned, offering the ability of such structures to effectively utilize a wide range of energies in the visible region. Composite nanostructures comprised of various classes of nanomaterials such as metal-doped semiconductor, plasmonic, and non-plasmonic metal NPs were investigated to perform the desirable solar-to-chemical transformations. First, we employed SiOx-loaded silver-doped silver chloride (SiOx/AgCl(Ag)) photocatalyst to investigate the role of metal-induced gap states in AgCl, a wide bandgap semiconductor. SiOx/AgCl(Ag) exhibit high catalytic performance and photostability after 10 cycles of the probe reaction, methylene blue (MB) degradation under visible light irradiation. The results indicate that the visible light absorption due to metal-induced gap states can be further improved by employing the SiOx NSs as supports that act as optical nanoantenna. We then studied the influence of NP size on the catalytic activity to understand the effect of size in promoting the generation and transfer of hot electrons to surface adsorbates. Our findings indicate that upon employing Ag NPs of different particle size (<10 nm and >10 nm) and normalizing for the optical absorption and moles of surface Ag atoms, the efficient generation and transfer of photoexcited hot electrons is favored in the small-sized Ag NPs (size <10 nm) than bigger Ag NPs. Next, we investigated the selective partial hydrogenation of nitroarene to N-aryl hydroxylamine using SiOx-loaded platinum (SiOx/Pt) photocatalysts. We found that change in the surface electronic structure of the small Pt NPs (size <5 nm) due to light illumination and surface modification (by adding suitable organic ligands), minimize the adsorption of the electron-rich hydroxylamine molecules and minimize their complete conversion to aniline, resulting in high N-hydroxylamine selectivity. Overall, our work shows that well-controlled composite nanostructures comprising of active catalyst loaded on dielectric SiOx NS supports that act as optical nanoantenna are a promising class of photocatalysts for driving photon-to-chemical transformations with high activity and product selectivity. / Chemistry