The photochemical water splitting reaction is of great interest for converting solar energy into usable fuels. This dissertation focuses on the development of inorganic nanoparticle catalysts for solar energy driven conversion of water into hydrogen and oxygen. The results from these selected studies have allowed greater insight into nanoparticle chemistry and the role of nanoparticles in photochemical conversion of water in to hydrogen and oxygen. Chapter 2 shows that CdSe nanoribbons have photocatalytic activity for hydrogen production from water in the presence of Na2S/Na2SO3 as sacrificial electron donors in both UV and visible light. Quantum confinement of this material leads to an extended bandgap of 2.7 eV and enables the photocatalytic activity of this material. We report on the photocatalytic H2 evolution, and its dependence on platinum co-catalysts, the concentration of the electron donor, and the wavelength of incident radiation. Transient absorption measurements reveal decay of the excited state on multiple timescales, and an increase of lifetimes of trapped electrons due to the sacrificial electron donors. In chapter 3, we explore the catalytic activity of citrate-capped CdSe quantum dots. We show that the process is indeed catalytic for these dots in aqueous 0.1 M Na2S:Na2SO3, but not in pure water. Furthermore, optical spectroscopy was used to report electronic transitions in the dots and electron microscopy was used to obtain morphology of the catalyst. Interestingly, an increasing catalytic rate is noted for undialyzed catalyst. Dynamic light scattering experiments show an increased hydrodynamic radius in the case of undialyzed CdSe dots in donor solution. In chapter 4 we show that CdSe:MoS2 nanoparticle composites with improved catalytic activity can be assembled from CdSe and MoS2 nanoparticle building units. We report on the photocatalytic H2 evolution, quantum efficiency using LED irriadiation, and its dependence on the co-catalyst loading. Furthermore, optical spectroscopy, cyclic voltammetry, and electron microscopy were used to obtain morphology, optical properties, and electronic structure of the catalysts. In chapter 5, illumination with visible light ([lambda]> 400 nm) photoconverts a red V2O5 gel in aqueous methanol solution into a green VO2 gel. The presence of V(4+) in the green VO2 gel is supported by Electron Energy Loss Spectra. High-resolution electron micrographs, powder X-ray diffraction, and selective area electron diffraction (SAED) data show that the crystalline structure of the V2O5 gel is retained upon reduction. After attachment of colloidal Pt nanoparticles, H2 evolution proceeds catalytically on the VO2 gel. The Pt nanoparticles reduce the H2 evolution overpotential. However, the activity of the new photocatalyst remains limited by the VO2 conduction band edge just below the proton reduction potential. Chapter 6 studies the ability of IrO2 to evolve oxygen from aqueous solutions under UV irradiation. We show that visible illumination ([lambda]> 400 nm) of iridium dioxide (IrO2) nanocrystals capped in succinic acid in aqueous sodium persulfate solution leads to catalytic oxygen evolution. While the majority of catalytic hydrogen evolution comes from UV light, the process can still be driven with visible light. Morphology, optical properties, surface photovoltage measurements, and oxygen evolution rates are discussed.

Troy Townsend's thesis explores the structure, energetics and activity of three inorganic nanocrystal photocatalysts. The goal of this work is to investigate the potential of metal oxide nanocrystals for application in photocatalytic water splitting, which could one day provide us with clean hydrogen fuel derived from water and solar energy. Specifically, Townsend's work addresses the effects of co-catalyst addition to niobium oxide nanotubes for photocatalytic water reduction to hydrogen, and the first use of iron oxide 'rust' in nanocrystal suspensions for oxygen production. In addition, Townsend studies a nickel/oxide-strontium titanate nanocomposite which can be described as one of only four nanoscale water splitting photocatalysts. He also examines the charge transport for this system. Overall, this collection of studies brings relevance to the design of inorganic nanomaterials for photocatalytic water splitting while introducing new directions for solar energy conversion.

Chalcogenide-Based Nanomaterials as Photocatalysts deals with the different types of chalcogenide-based photocatalytic reactions, covering the fundamental concepts of photocatalytic reactions involving chalcogenides for a range of energy and environmental applications. Sections focus on nanostructure control, synthesis methods, activity enhancement strategies, environmental applications, and perspectives of chalcogenide-based nanomaterials. The book offers guidelines for designing new chalcogenide-based nanoscale photocatalysts at low cost and high efficiency for efficient utilization of solar energy in the areas of energy production and environment remediation. - Provides information on the development of novel chalcogenide-based nanomaterials - Outlines the fundamentals of chalcogenides-based photocatalysis - Includes techniques for heterogeneous catalysis based on chalcogenide-based nanomaterials

Two-dimensional (2D) materials for photocatalytic applications have attracted attention in recent years due to their unique thickness-dependent physiochemical properties. 2D materials offer enhanced functionality over traditional three-dimensional (3D) photocatalysts due to modified chemical composition and electronic structures, as well as abundant surface active sites. This book reviews the applications of 2D-related nano-materials in solar-driven catalysis, providing an up-to-date introduction to the design and use of 2D-related photo(electro)catalysts. This includes not only application areas such as fine chemicals synthesis, water splitting, CO2 reduction, and N2 fixation, but also catalyst design and preparation. Some typical 2D and 2D-related materials (such as layered double hydroxides (LDHs), layered metal oxides, transition metal dichalcogenide (TMDs), metal–organic frameworks (MOFs), graphene, g-C3N4, etc.) are classified, and relationships between structure and property are demonstrated, with emphasis on how to improve 2D-related materials performance for practical applications. While the focus of this book will primarily be on experimental studies, computational results will serve as a necessary reference. With chapters written by expert researchers in their fields, Photocatalysis Using 2D Nanomaterials will provide advanced undergraduates, postgraduates and other researchers convenient introductions to these topics.

New, inexpensive and non-polluting energy technologies are of great importance for civilization. A promising source is solar energy, which can be photocatalytically converted into gaseous fuel or electricity. It has been hypothesized that nanomaterials may lead to improved photoelectrochemical (PEC), suspended photocatalytic, and photovoltaic cells. This particular field of study is vast considering the various ways nanomaterials can be synthesized, manipulated, and employed. Here, several different nanomaterials are studied as photocatalysts and as components in photoelectrochemical and photovoltaic cells. The purpose is to better understand charge transfer properties and energetics of these materials, and eventually, to help find a cheap, active, and sustainable photocatalyst for our ever-increasing energy demands. Chapter 1 gives a brief introduction to the field of nanomaterials for solar energy conversion. The motivation for this research is given, water-splitting photocatalysis is explained, and the various ways nanomaterials can be employed are reviewed. Chapter 2 explains how nanomaterials such as titanium dioxide and tungsten oxide can be used to photocatalytically decompose organic contaminants in wastewater while simultaneously producing electricity. Efficiency and power output analysis of derived photoelectrochemical cells revealed the highest published values for titanium dioxide electrodes under 395 nm illumination. Chapter 3 discusses calcium niobate (TBACa2Nb3O10, TBA = tetrabutylammonium) nanosheets as a photocatalyst for hydrogen evolution from aqueous methanol solution under UV illumination. Photoelectrochemical techniques were used to study the effects of ion modification of TBACa2Nb3O10 on the energetics, specifically the position of the Fermi energy. The data shows a direct relationship between the position of the Fermi energy and the relative rate of hydrogen production. Chapter 4 explains the fabrication and function of the first fractal electrode-based organic photovoltaic cells. Although the fractal electrode enhances the interfacial area between the light absorber and electrode, enhanced charge recombination results in reduced photocurrent for fractal silver. Chapter 5 gives a selection of the photoelectrochemical properties of iridium dioxide nanoparticles and single-crystal tungsten oxide nanosheets. The data can be used to calculate the photo-onset values for each material. Chapter 6 gives supporting information on calculating the power conversion efficiency of a PEC cell.

The conversion of solar energy into chemical fuel is one of the ,ÄúHoly Grails,Äù of twenty-first century chemistry. Solar energy can be used to split water into oxygen and protons, which are then used to make hydrogen fuel. Nature is able to catalyze both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) required for the conversion of solar energy into chemical fuel through the employment of enzymes that are composed of inexpensive transition metals. Instead of using expensive catalysts such as platinum, cheaper alternatives (such as cobalt, iron, or nickel) would provide the opportunity to make solar energy competitive with fossil fuels. However, obtaining efficient catalysts based on earth-abundant materials is still a daunting task. In this chapter, we review the advancements made with zirconium phosphate (ZrP) as a support for earth-abundant transition metals for the OER. Our studies have found that ZrP is a suitable support for transition metals as it provides an accessible surface where the OER can occur. Further findings have also shown that exfoliation of ZrP increases the availability of sites where active species can be adsorbed and performance is improved with this strategy.

More energy from the sun strikes Earth in an hour than is consumed by humans in an entire year. Efficiently harnessing solar power for sustainable generation of hydrogen requires low-cost, purpose-built, functional materials combined with inexpensive large-scale manufacturing methods. These issues are comprehensively addressed in On Solar Hydrogen & Nanotechnology – an authoritative, interdisciplinary source of fundamental and applied knowledge in all areas related to solar hydrogen. Written by leading experts, the book emphasizes state-of-the-art materials and characterization techniques as well as the impact of nanotechnology on this cutting edge field. Addresses the current status and prospects of solar hydrogen, including major achievements, performance benchmarks, technological limitations, and crucial remaining challenges Covers the latest advances in fundamental understanding and development in photocatalytic reactions, semiconductor nanostructures and heterostructures, quantum confinement effects, device fabrication, modeling, simulation, and characterization techniques as they pertain to solar generation of hydrogen Assesses and establishes the present and future role of solar hydrogen in the hydrogen economy Contains numerous graphics to illustrate concepts, techniques, and research results On Solar Hydrogen & Nanotechnology is an essential reference for materials scientists, physical and inorganic chemists, electrochemists, physicists, and engineers carrying out research on solar energy, photocatalysis, or semiconducting nanomaterials, both in academia and industry. It is also an invaluable resource for graduate students and postdoctoral researchers as well as business professionals and consultants with an interest in renewable energy.

As our world’s population is constantly growing, so also is the need to power the growth and spread of technology. The conversion of abundant solar energy into useable sources of fuel is an area of significant and vital research. Photocatalytic water splitting via suspended nanomaterials or photoelectrochemical cells has great promise for this purpose. This research focuses on the preparation and analysis of nanomaterials utilizing simple methods and earth abundant chemicals that will lead to cost-competitive methods to convert solar energy into an easily stored and transported fuel source. Specifically, our research seeks to better understand the methods of charge generation and separation in nanomaterial films and to quantify the limits of activity in suspended photocatalysts. Chapter 2 introduces a study on the nature of photovoltage generation in well-ordered hematite films under zero applied bias. The thickness of Fe2O3 nanorod films is varied by a simple hydrothermal synthesis and confirmed with TEM and profilometry measurements. Surface photovoltage spectroscopy (SPS) in the presence of air, water, nitrogen, oxygen, and under vacuum confirms photovoltages are associated with oxidation of surface water and hydroxyl groups and with reversible surface hole trapping on the 1 minute time scale and de-trapping on the 1 hour time scale with a maximum photovoltage of -130 mW under 2.0 eV – 4.5 eV illumination. Sacrificial donors (KI, H2O2, KOH) increase the voltage to -240 and -400 mW, due to improved hole transfer. The photovoltage is quenched with the addition of co-catalysts CoO[subscript x] and Co-Pi, possibly due to the removal of surface states and enhanced e/h recombination. Chapter 3 outlines a methodical exploration of the limits of water oxidation from illuminated ß-FeO(OH) suspensions. Well-defined akaganéite nanocrystals are able to produce oxygen gas from aqueous solutions in the presence of an appropriate electron acceptor. Optimal conditions were achieved by systematically varying the amount of catalyst, concentration of the electron acceptor, pH of the solution, and light intensity. A decrease in activity is shown to be the result of particle agglomeration after roughly 5 hours of illumination. A maximum O2 evolution rate of 35.2 μmol O2 h−1 is observed from an optimized system, with a QE of 0.19%, and TON of 2.58 based on total ß-FeO(OH). Chapter 4 continues to understand charge separation and transport in CdS nanorods. These nanomaterials are capable of catalytic proton reduction under visible illumination, but suffer from photo-corrosion resulting in decreased H2 production. SPS measurements show a maximum photovoltage of -230 mV at 2.75 eV and the charge separation is largely reversible. Coating the rods with graphitic carbon nitride (g-C3N4) creates a hole accepting protective layer than prevents oxidative loss of photo-activity. By adding platinum salts, additional photovoltage could be extracted through field induced charge migration from excited sub gap defect states and trap sites. The addition of a sacrificial reagent would either decrease or increase the photovoltage (depending on the reagent used) by creating additional bias in the films or charge recombination pathways. Finally, it was shown that varying the substrate has an effect on the platinum/substrate polarized charge injection. Chapter 5 Surface photovoltage is used to show for the first time the charge separation properties of Sn2TiO4, an n-type photocatalyst, a series of cuprous niobium oxides doped with tantalum (CuNb[subscript 1-y]Ta[subscript y]O[subscript x]), and a Cu (I) tantalum oxide Cu5Ta11O3.

Inorganic Two-Dimensional Nanomaterials provides an overview of the development on inorganic two-dimensional nanomaterials from computational simulation and theoretical understanding to applications in energy conversion and storage.

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