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.

This textbook covers the spectrum from basic concepts of photochemistry and photophysics to selected examples of current applications and research. Clearly structured, the first part of the text discusses the formation, properties and reactivity of excited states of inorganic and organic molecules and supramolecular species, as well as experimental techniques. The second part focuses on the photochemical and photophysical processes in nature and artificial systems, using a wealth of examples taken from applications in nature, industry and current research fields, ranging from natural photosynthesis, to photomedicine, polymerizations, photoprotection of materials, holography, luminescence sensors, energy conversion, and storage and sustainability issues. Written by an excellent author team combining scientific experience with didactical writing skills, this is the definitive answer to the needs of students, lecturers and researchers alike going into this interdisciplinary and fast growing field.

The book collects the lectures and the status reports delivered during the "Eighth International Conference on Photochemical Conversion and Storage of Solar Energy", IPS-8, held in Palermo (Italy) from 15th to 20th of July 1990. As usual, the main theme of the Conference was that of making the point about the trends and the developments of the studies related to the photochemical exploitation of solar energy and also to report the main lines of potential applications. Therefore the contributions reflect this point; they vary from those reporting basic and fundamental theories to those reporting cases of possible applications. For the sake of following the logical line which links each other the various contributions, we report the six areas in which the main theme of the conference was devided: (a) Electron and energy transfer in homogeneous and heterogeneous systems; (b) Photosynthesis: organized assemblies and biomimetic systems; (c) Photoelectrochemistry; (d) Photocatalysis: homogeneous and heterogeneous regime; (e) Environment: photochemical and photocatalytic processes; (f) Solar energy materials and photochemical engineering. It remains now to thank persons and institutions which made possible the organization of the Conference. The persons to thank are all the members of the International and National Organizing Committees and in particular Prof. A.Sclafani and Dr. L.Palmisano whose efforts were essential for the success of the Conference.

In this book, expert authors describe advanced solar photon conversion approaches that promise highly efficient photovoltaic and photoelectrochemical cells with sophisticated architectures on the one hand, and plastic photovoltaic coatings that are inexpensive enough to be disposable on the other. Their leitmotifs include light-induced exciton generation, junction architectures that lead to efficient exciton dissociation, and charge collection by percolation through mesoscale phases. Photocatalysis is closely related to photoelectrochemistry, and the fundamentals of both disciplines are covered in this volume.

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.

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 handbook comprehensively covers the field of inorganic photochemistry from the fundamentals to the main applications. The first section of the book describes the historical development of inorganic photochemistry, along with the fundamentals related to this multidisciplinary scientific field. The main experimental techniques employed in state-of-art studies are described in detail in the second section followed by a third section including theoretical investigations in the field. In the next three sections, the photophysical and photochemical properties of coordination compounds, supramolecular systems and inorganic semiconductors are summarized by experts on these materials. Finally, the application of photoactive inorganic compounds in key sectors of our society is highlighted. The sections cover applications in bioimaging and sensing, drug delivery and cancer therapy, solar energy conversion to electricity and fuels, organic synthesis, environmental remediation and optoelectronics among others. The chapters provide a concise overview of the main achievements in the recent years and highlight the challenges for future research. This handbook offers a unique compilation for practitioners of inorganic photochemistry in both industry and academia.

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.

This ACS Book presents studies of photoinduced processes in nanomaterials that fall into the category of basic research contributing to solar energy conversion. The team of editors and chapter authors focus on photophysical and photochemical processes at surfaces of semiconductor nanostructures that are related to photovoltaic and photocatalytic applications with a broader focus on time-resolved spectroscopic monitoring of related processes in photoactive materials. The book reports short, up-to-date reviews, recent experimental data, and computational results that all contribute to an atomistic description of electronic dynamics and charge transfer induced by optical excitations and lattice vibrations.

Power harnessed from the sun has the capacity to meet the energy demands of the entire planet. Here we present research in the areas of solar energy conversion accomplished by photochemical water splitting, to produce renewable chemical fuels, and by photovoltaics, to generate electrical power. The entire discussion takes place within the context of nanochemistry. Investigation of the novel properties developed by materials when they become very small offers us new insight into the field of chemistry and provides us with unique ways of improving existing solar energy conversion technologies. Nanocrystalline tungsten trioxide, nano-WO3, is presented as a new photocatalyst for water oxidation in the presence of a sacrificial electron acceptor. The monoclinic structure of the nanomaterial is analyzed by powder X-ray diffraction and electron microscopy. Optical spectroscopy data is consistent with quantum confinement in nano-WO3. Comparison of the nanomaterial with the bulk phase, via surface photovoltage spectroscopy and electrochemical analysis, demonstrates that the principle photochemical and photophysical properties of tungsten trioxide are conserved upon nanoscaling. These results indicate that nano-WO3 has potential as a functional replacement for bulk WO3 in applications incorporating nanomaterials, such as ultrathin solar cells. The effects of nanosheet size and defect concentration are investigated for the known photocatalyst calcium niobate, TBA[Ca2Nb3O10]. The dimensions of the nanosheets, and the edge defect concentration, are controlled by ultrasonication and analyzed by optical and vibrational spectroscopy and high-resolution electron microscopy. The rate of photochemical hydrogen evolution from water, in the presence of a sacrificial electron donor, is shown to decrease linearly with sheet size. Surface photovoltage spectroscopy indicates a correlation between nanosheet size and charge carrier concentration that is consistent with photocatalytic activity being limited by charge recombination in edge defect sites. TBA[Ca2Nb3O10] nanosheets have previously been shown to photocatalytically split water into hydrogen and surface-bound peroxides. Peroxide formation is a result of incomplete water oxidation and eventually leads to deactivation of the catalyst. We present here the functionalization of the nanosheets with metal oxide nanoparticles as potential water oxidation co-catalysts, in an attempt to promote complete water splitting. The functionalized materials are well characterized using electron microscopy and optical, infrared, and Raman spectroscopies. However, a reduction in photocatalytic activity is observed following functionalization that can be explained in terms of competitive light absorption, electron-hole recombination, and electron trapping within the metal oxides. Finally, we present studies performed during the development of a one-pot synthesis for titanium dioxide nanospheres coated with silver shells (Ag@TiO2). Nanoscale silver demonstrates surface plasmon resonance (SPR) upon light absorption, and the incorporation of SPR exhibiting core–shell particles is reported to increase the efficiency of photovoltaic devices. Here we use photogenerated electrons within TiO2 to reduce silver onto the material surface as nanoseeds. The effects of silver concentration, reaction temperature, and photodeposition time on seed morphology and dispersion are presented, following analysis by electron microscopy. An electroless plating method utilizing acetaldehyde to chemically reduce additional silver is explored as a technique for shell formation following surface seeding. However, optical spectroscopy data indicates that seeds continue discrete growth, rather than merging into a shell. Ultimately, consistent silver seeding could not be achieved and shell formation was unsuccessful. The results of these studies are consistent with the conclusion that silver nucleation is limited by the photogeneration of electrons in TiO2, active site chemistry, and the inherent weakness of the Ag-TiO2 interaction.