Stanford Synchrotron Radiation Lightsource

Many practical catalysts, illustrated by those used for fossil fuel conversion and vehicle exhaust clean-up, consist of expensive noble metals dispersed on high-area porous solid supports. When the metals are atomically dispersed and isolated from each other, they offer new properties and the highest efficiency of metal use—with each metal atom accessible to reacting molecules. But applications of supported noble metal catalysts are usually limited by the loss of accessibility of reactants to the metals that results from metal aggregation (sintering) during operation.

The biosynthesis of methane is significant because this molecule is both a good source of energy and a greenhouse gas. Despite its importance, the processes by which methane is made is not well understood. Methane is synthesized by methanogens, archaea found in anaerobic conditions like bogs and the guts of mammals. Only these microbes are able to perform the tricky reaction of turning hydrogen gas and carbon dioxide into methane and water.

When trash is burned for energy, a residue called bottom ash (BA) is left behind. Each year the European Union alone creates millions of tons of BA, which can be used for construction after treatment. It is concerning that BA may contain metals like copper and zinc that leach into the environment, potentially harming wild life and, people. The amount of these metals in the ash does not indicate whether the material is a potential hazard since these metals are more or less able to mobilize into the surrounding environment depending on factors like pH and the solubility of their chemical form. To better understand which chemical forms of copper and zinc exist in bottom ash and if there is much variation between different ashes, a team of scientists from Sweden analyzed six samples from different waste-to-energy plants.

While steady improvement of lithium-ion batteries has allowed electronic technologies to perform better, researchers are nearing a theoretical limit to lithium-ion battery capacity. One way to overcome this limit is to change the chemistry of materials to allow more electrons to exchange between anode and cathode per unit of material. Currently, LiCoO₂ lithium-ion batteries transfer one electron per unit of cathode, but other lithium-based materials may allow for higher capacity. A team of researchers has investigated the Li-rich layered sulfide Li₂FeS₂ and a novel analog LiNaFeS₂ as potential higher capacity alternatives since they can store 1.5 or more electrons per unit.

Radioisotope therapies improve on traditional chemotherapies by being finely targeted to only the diseased cells and leaving surrounding healthy cells unharmed. A promising radioisotope for therapeutic uses is ¹¹⁹Sb, which releases low energy Auger electrons that can kill cancer cells. A problem with widespread use of drugs using ¹¹⁹Sb is its short half-life of around 38 hours. A team of scientists from Los Alamos National Laboratory have developed a novel strategy for utilizing ¹¹⁹Sb.

While a small amount of copper is essential for living organisms, too much copper contaminating our soils can be toxic and pose a serious problem. Copper has an affinity for organic matter in soils, where it mainly exists in the two redox states Cu(I) and Cu(II). In soils that fluctuate in redox conditions, the mobility of copper through the environment can be hard to predict. Mofette sites, produced by CO₂ degassing usually found in seismically active areas, are good natural laboratories due to their wide range of soil redox conditions and of soil organic matter composition within a small area. Near the sites of CO₂ degassing, the soil is anoxic and organic matter does not decompose well. The soils transition to oxic conditions just a few meters away. A team of researchers studied the behavior of copper in the natural gradient of a mofette site in the Czech Republic.

Hydrogen sulfide (H₂S) is a poisonous and corrosive gas created in industrial and natural systems. Copper oxide (CuO), a crystalline solid, can be used to clean H₂S from emissions by forming various copper sulfide species, a reaction that is thermodynamically favorable but often does not go to completion in industrial applications.

Arsenic is a well-known toxin that can contaminate our drinking supplies. Understanding how arsenic finds its way into drinking water requires research into its interaction with environmental conditions that affect redox reactions, including interactions with iron, sulfur, and carbon.

Molecular hydrogen (H₂) is a promising carrier of energy for a future that uses more sustainable sources of fuel. H₂ created from splitting H₂O using renewable energy methods could result in no carbon footprint energy use. While methods of water splitting are being developed, reverse reactions are a problem.

The radioactive element uranium is well-known for its role in nuclear energy. People mine naturally occurring uranium from deep sandstone deposits called roll fronts. Scientists have long thought that abiotic chemical reactions that occur over millions of years resulted in formation of crystalline uranium. An international team of scientists has challenged this basic theory, finding evidence for a different genesis for uranium in roll front deposits. 

The element manganese can have complex interactions with the environment, depending on the prevailing conditions. Manganese(IV) is a strong oxidant but can also bind to environmental toxins and heavy metals, rendering them less harmful. Both geochemical and microbial processes affect the reactions of manganese(IV) in the environment. A team of researchers were interested in following the complicated reactions and mineral products produced during the reduction of manganese(IV) under different environmental conditions.

The practice of storing reclaimed or storm water by refilling an aquifer is called managed aquifer recharge (MAR). Advantages of MAR to regions vulnerable to drought or which have depleted aquifers include water storage for future use, reduced water loss of stored water from evaporation, and stabilization of the aquifers. However, refilling aquifers can change the chemistry, allowing naturally occurring toxins in aquifer sediments to dissolve into the water. Arsenic, a potential poison, is of particular concern, since use of MAR has led to arsenic-contaminated water.

The sun provides more energy than what could ever possibly be consumed. However, switching to solar energy to end our dependence on fossil energy resources is made difficult not merely by how much is consumed, but rather by the pattern of how energy is used: significant amounts are consumed by road and air transportation and must be provided “on board” in the form of fuels. This problem could be solved with new devices that convert sunlight into renewable fuels, for example, by driving a light-induced current between two electrodes that split water by electrolysis into hydrogen and oxygen. Currently, the limiting step for the viability of this process is the oxygen evolution reaction (OER) that takes place at the anode. 

A team of researchers from the Technical University of Denmark and  the SUNCAT Institute at the SLAC National Accelerator Laboratory and Stanford University has demonstrated the superior performance of nanoparticles of platinum-yttrium (Pt_xY) as catalysts for oxygen electroreduction.

Graphite and diamond are two distinct forms of the same element, carbon. Nevertheless, their properties could not be any more different. For instance, diamond is extremely hard and can be used in cutting tools. Graphite, on the other hand, is soft and used in pencils. Graphite can be converted into diamond in a process that usually requires very high pressure. However, scientists have recently suggested an alternative route to obtain diamond-like structures from graphite – at least on the nanoscale.

Uranium (U) is one of the most prevalent radionuclide contaminants in soils and groundwater across the world as a result of nuclear fuel production, weapons manufacturing, and research activities. The environmental risks posed by U are determined largely by the degree of its mobility, which strongly depends on redox conditions.  Under oxic conditions, U(VI) is soluble and forms stable complexes with carbonate and calcium in groundwater.

Recent work at SSRL has helped reveal a previously unrecognized wealth of bromine chemistry in the environment, where bromine in seawater has long been thought to exist as inorganic bromide, while bromides in soil were considered so unreactive that they've routinely been used as a hydrological tracer.

The reality bromine chemistry in the environment is much more complex. X-ray absorption spectroscopic (XAS) studies conducted by Leri, et al. at SSRL Beam Lines 2-3 and 4-3, as well as at the ALS and NSLS, reveal a complicated association between bromine and organic carbon in both sea water and soil.

The FeFe-hydrogenases are of great interest because they can catalyze both the forward and reversed dihydrogen uptake/evolution reactions. Under optimal conditions a single molecule of FeFe-hydrogenase can produce approximately 9000 molecules of hydrogen per second. This translates into a theoretical capacity for refueling the hydrogen tank of the Space Shuttle within 30 minutes. Thus, hydrogenases are considered as desirable biological targets for hydrogen-based energy production and utilization technologies.

Porous nanoscale materials often have useful properties because of their proportionally large surface areas. Now, UCLA scientists have devised a way to make porous germanium, a semiconductor used in fiber optics and electrical components. This discovery means that nanoporous materials could soon be used to develop new kinds of solar cells or highly sensitive electronic sensors.

The toxicity of arsenic is widely known, but perhaps less widely appreciated is that it's the level of toxicity critically depends on the chemical form. The fern Pteris vittata, is one of a small group of plants that actively accumulates to a startling degree - an arsenic hyperaccumuatlor. P. vittata absorbs arsenic from soil, typically present as the relatively benign arsenate, and changes its chemical form to arsenite, which is one of the more toxic kinds of arsenic. The plant thrives on this toxic regimen, and it most likely does this to defends itself from hungry herbivores. The ability of P. vittata to take up arsenic has generated much excitement because of potential applications for environmental cleanup of drinking water and of contaminated sites.

Billions of years ago, primitive bacteria developed a way to harness sunlight to split water molecules into protons, electrons and oxygen-the cornerstone of photosynthesis. Now, a team of scientists has taken a major step toward understanding this process by deriving the precise structure of the catalytic metal-cluster center containing four manganese atoms and one calcium atom (Mn₄Ca) that drives this water-splitting reaction. This catalytic center resides in a large protein complex, called photosystem II, found in plants, green algae, and cyanobacteria. The international team was led by scientists from LBNL, and includes scientists from Germany's Technical and Free Universities in Berlin, the Max Planck Institute in Mülheim, and from SSRL.

Research performed at SSRL has provided insight into why lead is so damaging to the healthy development of young children. Scientists from the University of Michigan and Northwestern University used x-ray absorption spectroscopy at SSRL to understand how lead can interfere with proteins that help transform DNA blueprints into working proteins that run the body.

Iron metals oxidize to rust, losing electrons and gaining positive charge. Iron metals typically exist in an oxidation state of +2 or +3 (2 or 3 electrons less than a neutral iron atom). However, chemists have long thought that iron compounds with even higher oxidation states play important roles in enabling chemical reactions in metal-containing proteins.

Changing the electronic structure of a metal in order to “tune” its affinity to catalytic reaction intermediates is a key element in catalyst design. Tailor-made catalysts with a carefully adjusted ratio of two or more different alloy components are particularly needed in fuel cells, which could efficiently power electric vehicles – without the range limitations of current batteries.

A new technology that acts like a giant underground filter is successfully beginning to clean up the uranium contaminating an aquifer in a remote Utah canyon. Uranium contamination in groundwater is a serious problem because the toxic metal can travel long distances in underground aquifers, which are vital sources of fresh water for people, animals and agriculture. Recent research at SSRL showed that the filters-called PRBs (permeable reactive barrier) do intercept uranium, but in an unexpected way that has important implications for monitoring, costs, and future technology selection.

Industrial activities have led to widespread chromium (Cr) contamination in the environment. Although Cr is an essential element for humans, the hexavalent form is toxic, mutagenic and carcinogenic. Consequently, the presence of Cr in the environment poses a serious threat to human and animal welfare. However, the toxicity of Cr is a function of oxidation state. For example, hexavalent Cr has a high solubility in soils and groundwater and, as a consequence, tends to be mobile in the environment.

Halogenated natural products play important roles as antibiotics, antifungals, and antitumor agents. The process of halogenation involves the replacement of a hydrogen with a halide (such as chloride or bromide), and is a challenging task for a synthetic chemist. However, the iron-containing enzymes in the haloperoxidase and halogenase families readily catalyze these reactions. It is thought that when this reaction occurs, the iron in the enzyme is at a high-valent Fe(IV) state, and that this species is responsible for removing a hydrogen atom (called an abstraction) from the substrate, creating a substrate radical, and that a halogen radical is subsequently transferred to the substrate to complete the halogenation reaction.

The continuous advancement of X-ray spectroscopic techniques allows us to probe the structure of biological machineries for smaller samples in more dilute concentrations and thus to ask tough scientific questions about problems that have not been possible in the past. Careful biochemical preparation and systematic analytical characterization resulted in galactose oxidase samples that could be interrogated by X-rays. This metalloenzyme contains a copper at its active site that is coordinated to a cross-linked tyrosine and cysteine ligand, which both are essential to convert alcohols and sugars to their oxidized aldehyde forms by oxygen molecule. The remarkable feature of this reaction that it is selective and does not results in formation of carboxylates (a form of vinegar).

In a similar way to your old pick-up truck rusting in the driveway, your body experiences a continuous battle against the elements. A constant barrage of oxidative stress attacks your cells and their constituent parts, including proteins. Like rust-proof paint on your vehicle, you have defense mechanisms that seek to prevent damage before it starts. But also like your trusty truck, once a weakness in the armor presents itself, it can spread rapidly — and often unnoticed — until you suddenly discover significant damage. Numerous diseases, as well as aging itself, are linked to uncontrolled oxidative processes that lead to irreversible damage and ultimately death. Understanding these oxidative processes may lead toward stopping and possibly even reversing damage.

Copper is an essential ingredient for animal and plant life. Some proteins specifically bind copper for both structural and catalytic purposes. Up until now, mononuclear copper(II) ion binding sites fit into two categories, type 1 and type 2, defined by both their functional roles, structures, and the physical properties of the interactions.

The world's animals depend on plants, plants depend on photosynthesis, and photosynthesis depends on iron. Despite a relative abundance of this element, iron in a form useable by plants can be rare. Living organisms require soluble iron, which generally comes from environments in flux since iron settles into stable minerals unavailable to life. Since around 30-40% of oceans are iron-limited, understanding the sources of soluble iron is critical to understanding oceanic ecosystems, which are responsible for taking significant amounts of carbon out of the air.

Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorous.  Although these six elements make up biomolecules such as nucleic acids, proteins, and lipids, it is theoretically possible that some other elements in the periodic table could serve similar functions.  In a paper published in Science, Wolfe-Simon et. al., describe a bacterium of the Halomonadaceae family, strain GFAJ-1 which appears to substitute arsenic for phosphorous to sustain its growth.

Researchers at SSRL have developed a new, more powerful way to probe the behavior of a key component in hydrogen fuel cells. The group, led by Daniel Friebel of SSRL and Anders Nilsson of SSRL and SIMES, coated a single crystal of rhodium with one layer of platinum atoms, creating a platinum catalyst that was in essence "all surface." The unique sample design allowed them to observe how the catalyst surface interacted with the type of acid–water environment typical of fuel cells.

The element chromium is found in the environment in two common forms: Cr(VI), which is easily absorbed by the human body, and Cr(III), which is not. The first of these in the form of chromates can have severe adverse effects on the human body, including cancerous tumor formation and gene damage.  Normally Cr(VI) forms are not present in the approximately one billion tons of coal used annually for electricity generation in the U.S., however, a fraction of the Cr(III) in coal can become oxidized during coal combustion ending up as a Cr(VI) component in fly-ash, the major waste product from coal combustion. 

Manganese, one of the most abundant metals in soils and rocks, is important to the health of the environment: As it cycles between manganese-II and nanocrystalline manganese-III/IV oxides, it plays an important role in controlling the cycle and transport of soil nutrients and contaminants.  Yet because the process is kinetically hindered, manganese will not oxidize rapidly in air; manganese needs a catalyst, often bacteria, to spur the process into action.

In the well-known Greek legend the touch of King Midas would convert anything to metallic gold. Recently, a team working at SSRL lead by Professor Jorge Gardea-Torresdey from the University of Texas at El Paso have shown that ordinary alfalfa plants can accumulate very small particles (nanoparticles) of metallic gold (1). The best-known materials that contain nanoparticles of metallic gold are gold colloids. These lack the familiar metallic luster, but show bright colors which range from red, violet or blue, depending upon the size of the nanoparticles (2,3). 

Sorption reactions on particle surfaces can dramatically affect the speciation, cycling and bioavailability of essential micronutrients (i.e. PO₄^3-, Cu, Zn etc.) and toxic metals and metalloids (i.e. Pb, Hg, Se, As) in soils and aquatic environments. Considerable attention has been focused on understanding metal sorption reactions at a molecular/mechanistic level and the effects of metal concentration, pH, ionic strength, and complexing ligands on the ways in which metal ions bind to the surfaces of common mineral phases such as Fe-, Mn- and Al-(hydr)oxides and clays. However, a significant fraction of mineral surfaces in natural environments are extensively colonized by microbial organisms, which can also be potent sorbents for metals due to the large number of reactive functional groups that decorate the cell walls and outer membranes of bacterial surfaces.