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Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2015)

The development of materials science and engineering in the past decades has been closely related to the emerging challenges associated with industrial and socio-economical requirements. Catalysis research has always been in a very central position in many different industry sectors. Learning from nature, materials research community has been long understood that the isolated catalytic components are no longer sufficient to meet new technological challenges. With more strict requirements of higher conversion and higher selectivity towards specific product(s), and lower energy demands during reactions, it is often very little room for singular catalyst material to play an efficient role. Instead, considerable attention has been placed in composite catalyst research. Rich knowledge in such regard has been obtained in plenty of catalysis research disciplines, like artificial photosynthesis, electrochemical energy conversion, tandem catalysis, as well as new types of conventional nanocatalysts with tentative compositions. Still, large gap in regard of nanocomposite catalyst materials is still difficult to be filled in near future. For instance, materials selection is an open field with uncountable possibilities, opportunities as well as problems. Synergetic effect is the utmost goal while its implementation is still questionable in most systems. Tandem catalysis represents revolutionary catalytic design philosophy, but its application in real life industry reactions is rare so far.

This dissertation depicts mainly the nanocomposite catalyst materials, and studies the synergetic effect between each component in different systems. It is divided into three fields. Firstly, in Part I, 2D material support in catalysis is studied and the influence of supporting material in catalytic activity and selectivity is discussed. It includes Chapter 3, in which graphene-hemin nanocomposite system was developed and explored through a simple wet synthesis route. It is applied in toluene oxidation reaction to examine the effect in primary C-H bond activation reaction. Also, the effect of graphene as support is investigated in detail. Secondly, in Part II, alloy nanocatalysts are designed and the synergetic effect between different components are studied. It includes Chapter 4 and 5. In Chapter 4, nanoporous palladium (Pd) catalyst is synthesized. It is then alloyed with gold (Au) component to form Au-Pd alloy catalyst, with maintained nanoporous morphology. Its superior oxidative catalytic efficiency is assessed in benzyl alcohol oxidation reaction and methanol electro-oxidation reaction. The alloy formation and the synergetic effect between Au and Pd components are studied. In Chapter 5, a nano-star shaped Au-Cu alloy catalyst is synthesized and used in CO2 reduction application. The high hydrocarbon yield is related to the alloy composition and rough surface morphology. Lastly, nanocomposite is widely used in photocatalysis, therefore the contribution of metallic and semiconductor components, and their integration effect is studied. It includes Chapter 6. In Chapter 6, tandem catalyst composed of TiO2 and Au/Pd nanowheel is fabricated. After annealing in inert environment, the nanocomposite is tested in benzimidazole synthesis reaction. It features a highly green reaction route with photocatalytic nature, and of remarkable yield in target molecule product. The role of each component and the synergetic effect is compared.

    Cover page: Design of Nanostructured Materials Systems for Selective Heterogeneous Catalytic Applications
    • Article
    • Peer Reviewed
    UCLA Previously Published Works (2017)
    Metallic nanoparticles are emerging as an exciting class of heterogeneous catalysts with the potential advantages of exceptional activity, stability, recyclability, and easier separation than homogeneous catalysts. The traditional colloid nanoparticle syntheses usually involve strong surface binding ligands that could passivate the surface active sites and result in poor catalytic activity. The subsequent removal of surface ligands could reactivate the surface but often leads to metal ion leaching and/or severe Ostwald ripening with diminished catalytic activity or poor stability. Molecular ligand engineering represents a powerful strategy for the design of homogeneous molecular catalysts but is insufficiently explored for nanoparticle catalysts to date. We report a systematic investigation on molecular ligand modulation of palladium (Pd) nanoparticle catalysts. Our studies show that β-functional groups of butyric acid ligand on Pd nanoparticles can significantly modulate the catalytic reaction process to modify the catalytic activity and stability for important aerobic reactions. With a β-hydroxybutyric acid ligand, the Pd nanoparticle catalysts exhibit exceptional catalytic activity and stability with an unsaturated turnover number (TON) >3000 for dehydrogenative oxidation of cyclohexenone to phenol, greatly exceeding that of homogeneous Pd(II) catalysts (TON, ~30). This study presents a systematic investigation of molecular ligand modulation of nanoparticle catalysts and could open up a new pathway toward the design and construction of highly efficient and robust heterogeneous catalysts through molecular ligand engineering.
      Cover page: Molecular ligand modulation of palladium nanocatalysts for highly efficient and robust heterogeneous oxidation of cyclohexenone to phenol.
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2015)
      Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercalated with methylammonium iodide to produce perovskite crystals. Structural and optical characterizations demonstrate that the resulting materials display excellent crystalline quality and optical properties. We further show that perovskite crystals can be selectively grown on prepatterned electrode arrays to create independently addressable photodetector arrays and functional field effect transistors. The ability to grow perovskite microplates and to precisely place them at specific locations offers a new material platform for the fundamental investigation of the electronic and optical properties of perovskite materials and opens a pathway for integrated electronic and optoelectronic systems.
        Cover page: Wafer-scale growth of large arrays of perovskite microplate crystals for functional electronics and optoelectronics
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