bluuebunny/crossref_metadata_2025_split huggingface dataset:
Americium and Curium: Radionuclides
Authors: Runde Wolfgang 
Published: December 2011

AbstractFollowing the element plutonium, americium and curium are the sixth and seventh elements in the actinide series. The primordial americium and curium isotopes that formed during the creation of the solar system billions of years ago have decayed away. Today, residual amounts of americium and curium isotopes present in nature are anthropogenic, originating from human activities such as nuclear weapons testing or nuclear energy generation. All americium and curium isotopes are highly radioactive and pose extreme health hazards to humans, especially when ingested or inhaled. Complexation reactions with environmentally relevant ligands, separation chemistry, the mechanistic studies of the processes that Am(III) and Cm(III) undergo at the solid–liquid interface in nature, and innovative process applications have been the focus of many studies during recent decades.In general, the trivalent oxidation state of americium and curium is the most stable under environmental conditions. As hard cations, the Am3+and Cm3+ions form strong complexes with hard donor ligands and adsorb readily on surfaces. In the absence of carbonate, hydrolysis leads to sparingly soluble Am(III) and Cm(III) hydroxide complexes. Americium and curium are commonly used in home smoke detectors and for oil‐well logging (241Am), and as radioisotope thermoelectric generators (244Cm).
PacificOcean: Radionuclides
Authors: Aoyama Michio 
Published: December 2011

AbstractThe main sources of anthropogenic radioactivity to the Pacific Ocean are fallout from atmospheric nuclear weapon testing. The releases from the nuclear fuel reprocessing plant and from the Chernobyl accident in 1986 are minimal in this region. Consequently, the radionuclide levels in the Pacific Ocean are low, about a few becquerel per cubic meter for137Cs in the surface water.137Cs,239, 240Pu (other transuranics), and90Sr are discussed in this article for the following reasons: (i)137Cs and90Sr, conservative in the open sea, are the most abundant anthropogenic radionuclides and the main contributors to human exposure and (ii)239, 240Pu are very long‐lived, nonconservative, and the most abundant among transuranics. The distributions and temporal change in these radionuclides in seawater and sediment are described. The current radionuclide levels in the Pacific Ocean are low and, therefore, of no concern from the radiological point of view.
IndianOcean: Radionuclides
Authors: Povinec Pavel P. 
Published: December 2011

AbstractThe distribution of global fallout radionuclides in Indian Ocean waters about four decades after their main injection from atmospheric nuclear weapons tests on the ocean surface is discussed. Recent data obtained in the framework of the WOMARS (Worldwide Marine Radioactivity Studies) and SHOTS (Southern Hemisphere Ocean Tracer Studies) projects are evaluated and compared with previous investigations carried out in the northern and southern Indian Ocean. The results indicate transport of surface waters labeled with radionuclides from the Mediterranean Sea, as well as from the Northwestern Pacific through the Indonesian Seas to the Indian Ocean. After passing the equator the waters circulate in the South Indian Ocean subtropical gyre, which accumulates radionuclide tracers and other contaminants on timescales of decades. This accumulation of contaminants in the Southern Indian Ocean is of environmental importance for the protection of the marine environment from land‐based contamination sources.
Arctic Ocean: Radionuclides
Authors: Zaborska Agata , Carroll JoLynn 
Published: December 2011

Abstract

This article presents an overview of the major sources, transport pathways, and fate of anthropogenic radionuclides in the Arctic marine environment. The dominant anthropogenic radionuclides present in Arctic seawater, sediments, and marine biota are cesium‐137 (
137
Cs), plutonium‐239 (
239
Pu), plutonium‐240 (
240
Pu), technetium‐99 (
99
Tc), and strontium‐90 (
90
Sr). Major sources contributing to the inventory of radionuclides in the Arctic Ocean and surrounding shelf seas include atmospheric fallout, European nuclear reprocessing facilities, the Chernobyl accident, and discharges from major Arctic rivers. Anthropogenic radionuclides from these sources are supplied to and redistributed within the Arctic Ocean via atmospheric, sea ice, currents, sediment, and river transport pathways. With the exception of a few locations, e.g., the underwater nuclear test site at Chernaya Bay, sediment, seawater, and biota activity concentrations in the Arctic are today very low, posing negligible biological and human‐health risks. However, the rate of warming of the Arctic is three times faster than other parts of the globe, raising the prospect of significant reorganization of system properties and processes with consequent changes to both the sources and fate of radionuclides in the Arctic in the decades to come.
OakRidgeReservation: Radionuclides
Authors: Jardine Philip M. , Brooks Scott C. , Watson David B. 
Published: December 2011

AbstractThe Department of Energy (DOE) facilities on the Oak Ridge Reservation (ORR) have a rich history of radionuclide separation technologies and research involving the conversion of uranium to plutonium for thermonuclear weapon parts during WWII and the Cold War era. During this period, tens of millions of curies of radioactive waste was typically disposed in unlined surface impoundments and shallow subsurface trenches. The disposal methods have resulted in a daunting challenge of remediating huge below‐ground inventories of legacy radioactive waste, since the scale of the problem is at the watershed level. The focus of this article is to provide an overview of past and current activities on the ORR that involve the use, disposal, and remediation of radionuclide isotopes. The aim of the article is to provide an improved understanding of why radioactive material was generated, how it was used and disposed of, and how it continues to interact with the environment.
BlackSea: Radionuclides
Authors: Egorov Victor , Gulin Sergey , Polikarpov Gennady , Osvath Iolanda 
Published: December 2011

AbstractAnthropogenic radionuclide pollution of the Black Sea originated primarily from the atmospheric nuclear weapon tests carried out during the late 1950s and early 1960s before the signing of the Test Ban Treaty in 1963, and after the Chernobyl nuclear power plant (NPP) accident in April 1986. Chernobyl atmospheric fallout deposited 1.7–2.4 PBq of137Cs into the Black Sea surface, which temporarily increased the137Cs inventory of the 0–50 m surface layer by a factor of 6–10 in comparison with its pre‐Chernobyl value. The contribution of Chernobyl‐origin90Sr (0.1–0.3 PBq) from atmospheric fallout was lower in comparison with that of137Cs. A subsequent90Sr input from the Danube and the Dnieper Rivers (about 0.16 PBq) was an important contribution to the budget of this radionuclide in the Black Sea, while the riverine137Cs input (0.02–0.03 PBq) was insignificant. The decrease of the137Cs inventory in the surface layer after Chernobyl accident has been mainly controlled by vertical mixing, loss through the Bosporus Strait, and radioactive decay. The loss through the Bosporus accounted for 2–2.5% of the137Cs inventory. In the case of90Sr, these processes have been compensated by river inputs from the Dnieper and Danube up to 1994–1995 and partially after 2000. The vertical mixing of137Cs and90Sr was mainly effective within the 0–200 m layer. Sediment inventories of137Cs in the Danube and Dnieper delta regions exceeded by one order of magnitude the values in the slope zone and two orders of magnitude those in the deep basin. Because of the self‐cleaning processes, the current levels of anthropogenic radionuclides are relatively low in all the components of the Black Sea environment, and therefore do not pose any radiological problem. Doses to marine biota from137Cs and90Sr are several orders of magnitude lower than those from natural210Po.
Fuel Cells: Enzymes and Microbes for Energy Production
Authors: Barrière Frédéric 
Published: December 2011

Abstract
The use of redox enzymes and bacteria as catalysts at the electrodes of fuel cells is reviewed with an emphasis on some inorganic aspects of the research. In biofuel cells, redox enzymes catalyze the oxidation of organic substrates like glucose at the anode or the reduction of electron acceptors like dioxygen at the cathode. Many of the redox enzymes have metal‐active sites that are of interest to the bioinorganic chemist. Moreover, efficient electrical linking between a redox enzyme and an electrode requires the mediation of a small electroactive molecule, capable of diffusing and shuttling electrons between the core of the enzyme and the electrode surface. These redox mediators may be coordination or organometallic complexes. In microbial fuel cells, the biocatalysts are living microorganisms, most often bacteria. At the anode, the bacteria metabolize organic substrates like sugars or acetate. In the absence of dioxygen or other natural electron acceptors, some species of bacteria may transfer electrons to the anode of a fuel cell. Different mechanisms for bacterial anodic electron transfer are proposed and discussed in this article. One common feature of these processes is the direct or indirect linking of the electrode surface to the outer‐membrane‐bound electron‐transfer chain of the respiratory system of bacteria. This system contains a chain of redox enzymes containing cytochrome‐type active sites that may be directly electrochemically addressed in some cases. At the cathode of microbial fuel cell, some bacteria may also accept electrons and catalyze the reduction of electron acceptors like nitrate, sulfate, and dioxygen. Given the importance of dioxygen reduction in most fuel cells, a perspective is given on the way inorganic chemistry may contribute to the design of efficient electrode catalysts through molecular, material, enzymatic, or biological approaches. Finally, the prospect of self‐sustained biological fuel cell is discussed with integration of plants with their anolyte as an in situ fuel provider in the form of root exudates, or enrichment of dioxygen in their catholyte with photosynthetic activity of algae. Although the emphasis is on the inorganic themes of biological fuel cell research, the important multidisciplinary approaches of the topic are put forward. This article also contains discussions on the relative performances and applications of both types of biological fuel cells.
Hydrogen Economy
Authors: Wells Stephen A. , Sartbaeva Asel , Kuznetsov Vladimir L. , Edwards Peter P. 
Published: December 2011

AbstractHydrogen technologies and fuel cells evoke, for many people, vision of a future in which electrical energy and heat can be generated not only cleanly but also noiselessly and efficiently—with only water as by‐product at the point of use. These technologies—particularly for transport applications—are viewed as a bridge to a sustainable and secure energy future. But despite its clear promise, hydrogen is today still largely only a potential energy carrier of the future; this chemical element is usually a key component of long‐term energy policies. But, as recently noted by Eames and McDowall: “…it is expectations about, and visions of, the future of hydrogen that are currently driving investment and research.”This article explores some of these expectations; in particular, we examine important scientific and technological issues concerning the production, storage, and utilization of hydrogen, as well as outlining the interrelated—and equally challenging—socioeconomic issues for a future hydrogen energy economy. We hope that this approach allows the reader to assess the complexities, challenges—and, of course, the considerable potential—of hydrogen and fuel cells in long‐term transport strategies. We illustrate the very considerable central role of chemistry in building innovative solutions to key areas of a future hydrogen energy economy.
Fuel Cells: Proton Exchange Membranes
Authors: Devanathan Ram 
Published: December 2011

Abstract

Proton exchange membrane, also known as polymer electrolyte membrane, fuel cells (PEMFCs) offer the promise of efficient conversion of chemical energy of fuel, such as hydrogen or methanol, into electricity with minimal pollution. Their widespread use to power zero‐emission automobiles as part of a hydrogen economy can contribute to enhanced energy security and reduction in greenhouse gas emissions. However, the commercial viability of PEMFC technology is hindered by high cost associated with the membrane‐electrode assembly (MEA) and poor membrane durability under prolonged operation at elevated temperature. Membranes for automotive fuel cell applications need to perform well over a period comparable to the life of an automotive engine and under heavy load cycling including start‐stop cycling under subfreezing conditions. The combination of elevated temperature, changes in humidity levels, physical stresses, and harsh chemical environment contribute to membrane degradation. Perfluorinated sulfonic acid (PFSA)‐based membranes, such as Nafion
®
, have been the mainstay of PEMFC technology. Their limitations, in terms of cost and poor conductivity at low hydration, have led to continuing research into membranes that have good proton conductivity at elevated temperatures above 120 °C and under low‐humidity conditions. Such membranes have the potential to avoid catalyst poisoning, simplify fuel cell design, and reduce the cost of fuel cells. Hydrocarbon‐based membranes are being developed as alternatives to PFSA membranes, but concerns about chemical and mechanical stability and durability remain. Novel anhydrous membranes based on polymer gels infused with protic ionic liquids have also been recently proposed, but considerable fundamental research is needed to understand proton transport in novel membranes and evaluate durability under fuel cell operating conditions. In order to advance this promising technology, it is essential to rationally design the next generation of PEMs on the basis of an understanding of chemistry, membrane morphology, and proton transport obtained from experiment, theory, and computer simulation.
Oxygen Production from Water: Molecular Catalysts
Authors: Llobet Antoni , Romain Sophie 
Published: December 2011

Abstract
This article presents an overview of the established basis needed for the oxidation of water to dioxygen, and thus the demands a catalyst needs to fulfill to be able to perform this reaction. It further describes the structure, redox properties, and performance of selected molecular catalysts that have been reported to be able to perform this difficult reaction and that can be considered as references in the field. The scarce reaction mechanism studies that have been described are also summarized and discussed. The article mainly deals with Ru complexes, because they constitute most of the available literature at the moment, and are classified as a function of their nuclearity. Other transition metal complexes of relevance based on Ir, Co, and Mn are also described. Finally, a few conclusions are drawn from the global description of all of the catalysts presented here, and the challenges and opportunities in the field are also discussed.
Methane–to–Methanol Conversion
Authors: Hashiguchi Brian G. , Hövelmann Claas H. , Bischof Steven M. , Lokare Kapil S. , Leung Chin Hin , Periana Roy A. 
Published: December 2011

AbstractNatural gas (NG) is an abundant, clean, underutilized fossil fuel that can augment or replace petroleum as the feedstock to fuels and chemicals. However, given the relatively high transportation costs for this highly volatile gas, utilization of NG will only be possible if inexpensive, efficient, large‐scale technologies can be developed tochemicallyconvert NG to liquids feedstocks (e.g., long chain alkanes or methanol). Current syngas‐based technologies can carry out this chemical conversion with very high carbon yield (∼70%) while utilizing the only economically viable co‐reactant on this enormous scale: dioxygen or ideally air. However, despite these attractive characteristics, these processes are too expensive to displace petroleum primarily due to the high capital costs associated with the high temperatures required to generate syngas. Substantial effort toward the development of less expensive, lower temperature (<250 °C) processes for the selective, high‐yield oxidative conversion of methane, the major component of NG, to functionalized products has yielded a number of potential systems. This article is focused on one very promising approach: the use of homogenous organometallic and/or inorganic complexes in liquid solutions to mediate the oxidative conversion of methane. Heterogeneous (gas/solid) systems are not covered. Considering the ultimate goal of replacing petroleum with NG, we have organized this article with respect to both fundamental chemistry as well as the important practical considerations of whether or not systems can utilize dixoygen as the ultimate co‐reactant. Two fundamentally different mechanistic strategies have emerged: (i) the use of coordination catalysts that coordinate and cleave the CH bond of methane (defined as CH activation) or that coordinate and activate the co‐reactant (defined as oxidant activation), and (ii) the use of chain reactions based on reactive species such as free radicals or other chain carrying species. Systems that fall into these two categories are further categorized with respect to whether or not oxygen is or can be utilized as the ultimate co‐reactant. The goal is to provide the reader with an efficient way of quickly finding or classifying the rapidly growing body of literature by reaction mechanism and co‐reactant utilized.
Hydrogen Production from Water: Photocatalysis
Authors: Arachchige Shamindri M. , Brewer Karen J. 
Published: December 2011

Abstract
Photocatalytic hydrogen production from water provides an attractive but challenging approach to meeting our global energy needs. Design and development of systems that utilize visible light to drive the energetically favorable, multielectron reduction of water to produce hydrogen fuel have been of long‐term interest. Addressing the challenges of efficient harvesting of solar energy to produce transportable fuels requires ongoing, sustained research in this field. Current technologies utilize photobiological methods, photoelectrochemical methods, and molecular photocatalysis. This article focuses on the recent progress of proton or water reduction using supramolecular photocatalysts. These photochemical molecular devices often couple charge‐transfer light absorbers (LAs) to reactive metals in complex molecular architectures. Linking multiple components into large molecular assemblies allows for applications requiring complex functions. Early successes in supramolecular photocatalysts for solar hydrogen production are summarized. The redox, excited state properties, and photochemical properties of supramolecular systems applicable in photocatalytic hydrogen production are presented. Fundamental studies of the perturbations of subunit properties upon incorporation into supramolecular arrays are paramount to their successful application in this forum. Optical excitation typically affords a metal‐to‐ligand charge‐transfer state that is quenched by electron transfer, providing reduced complexes with reactive metals able to deliver the electrons to substrates. Sacrificial electron donors provide coupling to oxidative chemistry, allowing independent study of photocatalysts and hydrogen production schemes. Supramolecular chemistry allows modulation of redox, photophysical, and photochemical properties by component modification. Coupling multiple LAs to an electron acceptor, which, when reduced by multiple electrons, provides photoinitiated electron collectors (ECs). Photoinitiated ECs, which collect multiple electrons on a reactive rhodium center with the supramolecular architecture remaining, reduce water to hydrogen fuel. Mixed‐valence systems that promote HX reduction to produce hydrogen have also been described. Coupling of charge‐transfer LAs to cobalt, iron, palladium, or platinum is a topic of recent interest in the design of water reduction photocatalysts. The general design considerations for the development of supramolecular assemblies that function as photocatalysts for proton reduction are discussed, providing valuable insight into engineering efficient solar hydrogen production catalysts for water reduction. Mechanistic studies remain important to understanding this complex multielectron photochemistry, which will aid in future molecular design. Much remains to be mastered in this complicated, multielectron photochemistry but recently there is increased awareness and interest in this field.
Photosynthesis, Artificial: Progress in Swedish Consortium
Authors: Ott Sascha , Styring Stenbjörn , Hammarström Leif , Johansson Olof 
Published: December 2011

Abstract

Mimicking energy conversion processes in nature using molecular systems is a promising approach for future solar fuel production. The Swedish Consortium for Artificial Photosynthesis is involved in the design, preparation and functional study of many of the key components needed for a homogeneous approach to artificial photosynthesis, building on principles from photosystem II (PSII) and [FeFe] hydrogenases. Ruthenium(II) polypyridyl complexes have played an important role as photosensitizers. Several strategies have been developed for their preparation, and a novel approach to improve the photophysical properties of bistridentate complexes involving six‐membered chelates for more octahedral coordination was recently introduced. The [Ru(dqp)
2
]
2+
complexes (dqp is 2,6‐di(quinolin‐8‐yl)pyridine) combine the desired structural properties for easy access to linear donor–acceptor assemblies, while maintaining microsecond luminescent lifetimes of their
3
MLCT (metal‐to‐ligand charge transfer) excited states. The synthesis of these chromophores is now well established, and the recent realization of donor–photosensitizer–acceptor assemblies shows that photoproduced charge‐separated states can be formed in high yields (ϕ ≥ 95%). Beyond such single‐photon/single‐electron events, charge accumulation at potential catalytic sites is crucial for multielectron redox reactions. Covalently linked Ru
II
Mn

x

(
x
= 1,2) complexes as PSII mimics have been investigated to understand chromophore–quencher (Mn quenchers) interactions, to promote desired electron transfer processes, and suppress undesired competing reactions. The Mn units often have large inner reorganization energies upon oxidation or reduction, which make them unusually slow electron donors and/or acceptors in photoinduced charge‐separation schemes. Charge accumulation and water splitting, however, require the management of
both
protons and electrons, which controls the electron transfer processes by proton‐coupled electron transfer (PCET). Studies on Ru
II
Tyr complexes incorporating pendant bases led to an understanding of the effect of hydrogen‐bonding on electron transfer rates. In analogy to the electron donor side, bioinorganic models of the [FeFe] H
2
ase active site are targeted for the electron acceptor side, with the ultimate goal to realize molecular catalysts that produce H
2
at similar high rates and low overpotential as the enzymes. Certain ligand sets create basic sites around the Fe centers that are protonated in the presence of acid and are thus models of late intermediates in the enzymatic catalytic cycle. Furthermore, synthetic Fe
2
complexes catalyze the electrochemical reduction of protons. In combination with a photosensitizer, they can also be used in photochemical schemes and are currently used to produce H
2
photochemically, with turnover rates up to 200.