Metallic nanocrystals have gained growing interest in photocatalysis applications due to their robust nature for multicycle operation, strong light absorption, and relatively new catalytic mechanisms. Historically, photocatalysis induced by localized surface plasmon resonance (plasmon resonance for short) of these particles has been studied widely for more than a decade, but photocatalysis originating from interband transitions is still underexplored. In order to build a comprehensive map from photon utilization to hot-carrier harvesting, and related photocatalysis, the systematic comparison between plasmon resonance and interband transition needs to be conducted in light of hot carriers-mediated reaction. The energy levels, population, dynamics, and heating effect of those hot carriers, and as followed, the charge transfer, reaction pathway, and kinetics are all necessary to be discussed. In this dissertation, the physical picture and related properties of interband transition and plasmon resonance are reviewed, then some systematic approaches to evaluate these two excitations are demonstrated. As follows, the porous Palladium nanoparticles as the model catalysts with dominant spectra features corresponding to the interband transitions were employed for mechanistic insights. We have demonstrated that under shorter wavelengths, deeper holes in the d-band can catalyze the oxidative addition of aryl halide R-X onto Pd0 at the nanoparticles’ surface to form R-PdII-X complex, thus accelerating the rate-determining step of the catalytic cycle, eventually increase the quantum yield of photocatalyzed Suzuki-Miyaura reactions. In the meantime, we have proved and quantified the effect of photocharging towards nanoparticle photocatalysis, as an underlying and often overlooked mechanism. We have built a proportional relation between accumulated charge and separate catalytic performance, which should deserve more attention in the future. Furthermore, we have been exploring the possibility of using earth-abundant metals for sustainable photocatalysis and utilizing the intrinsic interband transitions in these metals to search for new catalytic properties. Combined with the electronic and band structure of Au, Pd, and Co metals, we have rationalized the interband transitions in the metal-adsorbate hybridized states of those three metals and confirmed the contribution of both interaction strength between metal and adsorbates and energy states of hot carriers from interband transitions to photocatalysis. And the cobalt-based metallic nanoparticle photocatalysts were proved to be a good candidate for designing better energy alignment between the d-band structure and interband transition than Au and Pd nanoparticles, which leads us to shift from noble to non-noble metallic nanoparticle photocatalyst and a sustainable future. Eventually, we have provided some future perspectives towards the design for non-noble-metal-based nanoparticle photocatalysts and related mechanistic insights of the hot-carrier behavior from interband transitions.

The paper examines the forestland conversion in the period 2001-2005 and its socioeconomic determinants affecting such a change in Kien Luong district of southern Vietnam using Geographic Information Systems (GIS), Remote Sensing (RS), and multiple regression techniques. The land use/ land cover (LULC) classes of the years 2001 and 2005 were in turn classified from Landsat ETM Plus 2001 and digitized from the district land-use map 2005. Corresponding socioeconomic data to the derived LULC classes were aggregated for the multiple regression analysis of determinants of the forestland conversion. The findings indicated that the loss of forestlands was driven by the quick growth of the rural economy in which the two largest contributors were the prompt expansion of agricultural and aquaculture lands. Such a land-use change initially hampered the agricultural development and ecological services. Addressing land-use suitability for production systems and socio-environmental costs of the changes was therefore an urgent need for the aim of more effective policies of utilization and management of land resources.

Metallic nanoparticles have tunable electrochemical properties that make them suitable for catalyzing redox reactions. Thus, understanding how their reduction potentials respond to changes in particle size and light excitation is important for predicting their chemical stability and catalytic activity. However, establishing their standard reduction potentials through voltammetry has been met with technical challenges, specifically those introduced by the support. To get around this issue, an alternative approach based on Galvanic equilibration was adapted to determine the standard reduction potentials of colloidal NPs, thus avoiding the substrate effects associated with the support. This approach opens the door to exploring various factors that cause the nanoparticle reduction potentials to shift. Factors such as light absorption, changes in particle size, and local environmental effects will be discussed using theoretical models and experimental evidence to help us understand the magnitude of their impacts. Lastly, this approach can be adapted to investigate other factors important to catalysis, including crystallographic shape and atomic arrangement at the surface.First, Chapter 1 provides a historical context of metallic nanoparticles, from their early uses in decorative artifacts to modern chemical catalysis. Their early uses in art pieces stemmed from their unique optical properties. These optical properties were later determined to result from localized surface plasmon resonance, which became the foundation of metal nanoparticle-driven photocatalysis. Improvements in synthetic and characterization methods made it possible to study in depth their optical, catalytic, and chemical and physical properties concerning particle size. Their electrochemical properties are especially important for understanding their chemical stability and catalytic activity. With great success, such properties have been quantified for substrate-supported metallic nanoparticles through electrochemical methods such as anodic stripping voltammetry. Towards the end of the chapter, we discuss the limitations of voltammetry and how a galvanic equilibration approach can address such issues. Chapter 2 explains the principles behind the Galvanic equilibration approach in greater detail. This approach allows measuring the standard reduction potentials of spherical AuNPs freely suspended in solution to better understand how they respond to a change in size and the stabilizer ligands without the influence of the substrate supports. As the NPs decrease in size, their reduction potentials shift towards negative values that can be observed by a shift in their equilibrium constant when coupled to a redox probe. Furthermore, the ligand stabilizers such as quaternary ammonium surfactants are shown to also influence the reduction potentials. These surfactants participate in the redox reactions by interacting with the gold complexes formed during Galvanic equilibration. As a result, surfactants like CTAB significantly lower the standard reduction potentials of the gold nanoparticles, making them more electrochemically reactive. At the end of this chapter, the advantages of using the galvanic equilibration method for measuring the reduction potentials are summarized, and an outlook is given. Chapter 3 then takes the galvanic equilibration approach to investigate how light absorption induces a shift in the reduction potential. When metallic nanoparticles absorb light, they generate high-energy (hot) electrons and holes (carriers) that can be used to drive chemical transformations on the surface. The efficiency and selectivity of these chemical transformations can be tuned by parameters such as photon flux and energy. For noble metal nanoparticles, how carrier generation is also dependent on the mode of excitation, which include interband and localized surface plasmon resonance. For instance, exciting the NPs at the localized surface plasmon resonance region generates hot electrons relative to the hot holes. On the other hand, exciting at the interband region of AuNPs generates very hot holes relative to the hot electrons. By exciting at the interband region, for example, we can use the high-energy hot holes to catalyze the main oxidation reactions while scavenging the “warmer” electrons using sacrificial compounds. This process can also induce photocharging by selectively harvesting the hot holes and allowing the hot electrons to relax to the ground state and accumulate in the nanoparticle. This photocharging process raises the NP's Fermi level, which can be measured through Galvanic equilibration. The results show that shorter excitation wavelengths induce the largest photocharging and shift the reduction potentials more negatively than longer wavelengths. This observation implies that catalytic activity in metallic nanoparticles can be tuned by light, especially for redox transformations. Finally, Chapter 4 summarizes the work presented in this dissertation and discusses how galvanic equilibration can be used to study other physical and chemical phenomena, such as the shape effects on the electrochemical properties of NPs. For crystalline nanoparticles, different shapes are dominated by one or more kinds of facets with different surface tension. Because the surface Gibbs free energy depends on the surface tension, their electrochemical properties should vary amongst nanoparticles dominated by different facets. Thus, along with excitation wavelength, size, and stabilizer ligands, the NP shape can also be used to tune metallic NPs’ electrochemical stability and catalytic activity.

Many chemical reactions occurring at aqueous interfaces show different kinetics and thermodynamics than the same reactions occurring in the bulk. The nature of these chemical reactions is central in understanding environmental, industrial, and biological processes; but remains incompletely understood due to its complexity and experimental difficulties in tuning and characterizing reactions at aqueous interfaces. In this dissertation, different experimental approaches are utilized to generate large, well-characterized aqueous interfaces for kinetic studies of chemical reactions. Chapter 1 introduces deviations of chemistry at aqueous interfaces that can alter physiochemical properties of chemical processes. In chapter 2, I study mechanistic rate accelerations of organic reactions at the organic-water interface and find that free OH groups of interfacial water molecules play an essential role in catalysis. In chapter 3, I revisit the effects of electric fields at the air-water interface of water microdroplets on directly converting water into hydrogen peroxide which is thermodynamically unfavorable in solution. Contrast to previous reports, no hydrogen peroxide production is observed in water microdroplets when tuning the electric fields at droplet surfaces. In chapter 4, I discuss claims of spontaneous hydrogen peroxide formation at the air-water interface and pinpoint potential experiments that can help to clarify them. Chapter 5 is the conclusion of the work presented in this dissertation.

Vibrational spectroscopy is a powerful tool for structural characterization. Modern spectroscopy has been used ultrashort laser pulses in infrared region to monitor the structure evolution of species involving in chemical reaction. This spectroscopic technique can give dynamics of chemical reaction in ultrafast timescale, helping us understand the reaction mechanism in great detail. In this thesis, a wide range of ultrafast dynamics in solution triggered via photochemical reactions has been investigated: the photoisomerization mechanism of solar storage molecules (Fulvalene)tetracarbonyldiruthenium, the photo-inactive of analog molecules (Fulvalene)tetracarbonyldiiron, the spin state and reactivity of 14-electron species Fe(CO)3 and the heat transfer from various photochemical reaction to solvent. Finally, the dynamics of molecular rotational diffusion was also investigated to measure the effect of molecular mass on rotational motion of small solute in solution. The trends discovered from these prototypical complexes are expected to be applicable to other organometallics complexes. These results will have a great contribution to the ultrafast spectroscopy as well as the synthesis research community.