Glenn A Waychunas

Lawrence Berkeley National Laboratory | LBL · Geochemistry Department

Silicate sorption on ferrihydrite surfaces, as monomers, oligomers, and polymers, strongly affects ferrihydrite crystallinity, thermodynamic stability, and surface reactivity. How these silicate species bind on ferrihydrite surfaces is, however, not well understood. We have determined silicate binding geometries using a combination of X-ray absorpt...

Despite years of study, quantitative models for the nucleation and growth of metal oxyhydroxide nanoparticles from aqueous solution have remained elusive. The problem is complicated by surface adsorption, which causes the stoichiometry of the nucleus to differ from that of the bulk precipitate and causes the surface tension of the precipitate-water...

Iron oxides and oxyhydroxides form via Fe3+ hydrolysis and polymerization in many aqueous environments, but the pathway from Fe3+ monomers to oligomers and then to solid phase nuclei is unknown. In this work, using combined X-ray, UV-vis, and Mössbauer spectroscopic approaches, we were able to identify and quantify the long-time sought ferric speci...

Nucleation is a fundamental step in crystal growth. Of environmental and materials relevance are reactions that lead to nucleation of iron oxyhydroxides in aqueous solutions. These reactions are difficult to study experimentally due to their rapid kinetics. Here, we used classical molecular dynamics simulations to investigate nucleation of iron hyd...

The sorption of Pu(VI) and Pu(V) onto manganite (MnOOH) and Hausmannite (Mn3O4) was studied at pH 5. Manganite sorbed 21-24% from a 1x10-4 M plutonium solution and the hausmannite removed between 43-66% of the plutonium. The increased sorption by hausmannite results from its larger surface area (about twice that of manganite) plus a larger number o...

Aqueous dissolution processes are not well understood on the molecular scale ( 1 ), and this has led to controversy, notably in geochemical systems ( 2 , 3 ). Charging of a solid surface, either by substitution of ions with a different valence (e.g., Ca2+ for Na+) or by chemical binding of charged species from solution, orients the dipole moments o...

Induced mineral precipitation is potentially important for the remediation of contaminants, such as during mineral trapping in carbon or toxic metal sequestration. Prediction of precipitation reactions is complicated by the porous nature of rocks and soils and their interaction with the precipitate, introducing transport and confinement effects. He...

Interfacial free energies often control heterogeneous nucleation of calcium carbonate (CaCO3) on mineral surfaces. Here we report an in situ experimental study of CaCO3 nucleation on mica (muscovite) and quartz, which allows us to obtain the interfacial energies governing heterogeneous nucleation. In situ grazing incidence small angle X-ray scatter...

Nucleation is the seminal event in formation of new mineral phases. The subject has a long history, finding its modern roots in the work of Gibbs in the late 1800’s (Gibbs 1876, 1878) and continuing through the efforts of Stransky and others in the mid-20th century (Gutzow 1997). What emerged has come to be known as classical nucleation theory (CNT...

Sulfate adsorption on mineral surfaces is an important environmental chemical process. However, the structure of sulfate adsorption complexes has remained uncertain. In this study, we have determined the S−Fe distance of sulfate inner-sphere adsorption complexes on iron (Fe) oxyhydroxide (ferrihydrite) surfaces under air-dried conditions using sulf...

An emerging area in chemical science is the study of solid-phase redox reactions using ultrafast time-resolved spectroscopy. We have used molecules of the photoactive dye 2',7'-dichlorofluorescein (DCF) anchored to the surface of iron(iii) oxide nanoparticles to create iron(ii) surface atoms via photo-initiated interfacial electron transfer. This a...

Recent experimental observations of the onset of calcium carbonate (CaCO3) mineralization suggest the emergence of a population of clusters that are stable rather than unstable as predicted by classical nucleation theory. This study uses molecular dynamics simulations to probe the structure, dynamics, and energetics of hydrated CaCO3 clusters and l...

Much of the bioavailable and geochemically reactive iron in aerobic, circumneutral settings is fre- quently found in the form of nanoscale particles of a hydrated iron(III) oxyhydroxide phase known as ferrihydrite. Developing useful structural descriptions of defective nanophases such as ferrihydrite has long posed significant challenges. Recently,...

Pressed for time: Amorphous calcium carbonate (ACC) undergoes a reversible amorphous-amorphous phase transition at 10 GPa, adopting an aragonite-like local order. This result suggests a mechanism by which Mg(2+) -a cation with smaller ionic radius than Ca(2+) -modifies the local order of ACC to an aragonite-like order by helping to decrease the mol...

This chapter addresses what is known about the molecular structure at several aqueous‐metal oxide interfaces, including near surface water. It indicates how improvements in this knowledge from new interface sensitive methodology aids our understanding of how these systems affect reaction progress. The chapter considers recent approaches via...

The structure of ferric iron (Fe(3+)) dimers in aqueous solutions has long been debated. In this work, we have determined the dimer structure in situ in aqueous solutions using extended X-ray absorption fine structure (EXAFS) spectroscopy. An Fe K-edge EXAFS analysis of 0.2 M ferric nitrate solutions at pH 1.28-1.81 identified a Fe-Fe distance at ∼...

Electron mobility within iron (oxyhydr)oxides enables charge transfer between widely separated surface sites. There is increasing evidence that this internal conduction influences the rates of interfacial reactions and the outcomes of redox-driven phase transformations of environmental interest. To determine the links between crystal structure and...

Early stage amorphous precursors provide a low energy pathway for carbonate mineralization. Many natural deposits of carbonate minerals and biogenic calcium carbonate (both amorphous and crystalline) include significant amounts of Mg. To understand the role of magnesium-containing amorphous precursors in carbonate mineralization, we investigated th...

The phases and stability of ferric iron products formed early during neutralization of acid mine drainage waters remain largely unknown. In this work, we used in situ and time-resolved quick-scanning X-ray absorption spectroscopy and X-ray diffraction to study products formed between 4 min and 1 h after ferric iron sulfate solutions were partially...

The precipitation of carbonate minerals-mineral trapping-is considered one of the safest sequestration mechanisms ensuring long-term geologic storage of CO(2). However, little is known about the thermodynamic factors controlling the extent of heterogeneous nucleation at mineral surfaces exposed to the fluids in porous reservoirs. The goal of this s...

Sum frequency vibrational spectroscopy (SFVS) was used to study the structure of the protonated α-Al(2)O(3) (11 ̅20), and water/α-Al(2)O(3) (11 ̅20) interfaces as a function of pH. By combining SFVS spectra with an oxygen-terminated model suggested by x-ray reflectivity, we are able to understand several details of the protonated α-Al(2)O(3) (11 ̅2...

Sorption of contaminants onto mineral surfaces is an important process that can restrict their transport in the environment. In the current study, uranium (U) uptake on magnetite (111) was measured as a function of time and solution composition (pH, [CO(3)](T), [Ca]) under continuous batch-flow conditions. We observed, in real-time and in situ, ads...

Sequestration of uranium (U) by magnetite is a potentially important sink for U in natural and contaminated environments. However, molecular-scale controls that favor U(VI) uptake including both adsorption of U(VI) and reduction to U(IV) by magnetite remain poorly understood, in particular, the role of U(VI)-CO(3)-Ca complexes in inhibiting U(VI) r...

Early stage development of ferric iron oxyhydroxide (FeOOH) nanoparticles from bicarbonate-neutralized Fe2(SO4)3 solutions was investigated using time-resolved UV-Vis spectroscopy and quick extended X-ray absorption fine structure (Q-EXAFS) spectroscopy. Two neutralization ratio ( h =[HCO3-]/[Fe3+]) of 1 and 2 were used. The neutralized systems cha...

Corrosion of uraninite (UO2) - a surface-mediated process - is fundamental in controlling uranium contamination and mobility in the environment, the performance of nuclear power systems, and the stability of nuclear waste. The structure of hydrated uraninite-water interfaces under pristine and oxidized conditions is seminally important to uraninite...

Sum frequency vibrational spectroscopy was used to study the interfacial arrangement of ethanol molecules at the vapor/α-Al2O3(11̅02) and α-Al2O3(11̅02)/ethanol liquid interfaces. The spectra in the C–H range show that ethanol molecules adsorbed from vapor onto an α-Al2O3(11̅02) surface have a well-defined anisotropic arrangement following the stru...

Sum frequency vibrational spectroscopy was used to study the structure of water/α-Al2O3 (11̅02) interfaces at different pH values. The OH stretch spectra are dominated by interfacial water contributions at lower frequencies and by bonded hydroxyls on the Al2O3 surface at higher frequencies. Protonation and deprotonation of various oxide functional...

It is a special pleasure for me, and a distinct honor, to introduce the 2010 MSA awardee, Benjamin Gilbert. Liking science from early youth, Ben started his physics studies at Cambridge University, ultimately selecting a project that connected biology with physics as much as possible: the interaction of proteins with surfaces. This was to be, a po...

The local structure of aqueous metal ions on solid surfaces is central to understanding many chemical and biological processes in soil and aquatic environments. Here, the local coordination structure of hydrated Zn(II) at water-TiO(2) interfaces was identified by extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge struct...

Sum-frequency vibrational spectroscopy was used to study the protonated R-plane (1102) sapphire surface. The OH stretch vibrational spectra show that the surface is terminated with three hydroxyl moieties, two from AlOH(2) and one from Al(2)OH functional groups. The observed polarization dependence allows determination of the orientations of the th...

Using silver K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, two different samples of silver-containing manganese oxide were analyzed in the fluorescence mode. For the first sample, silver ions from solution were sorbed onto one synthetic manganese oxide phase, namely cryptomelane (KxMn8O16, where l<x<2). The second sample was...

The crystal structure of magnetite nanoparticles may be transformed to maghemite by complete oxidation, but under many relevant conditions the oxidation is partial, creating a mixed-valence material with structural and electronic properties that are poorly characterized. We used X-ray diffraction, Fe K-edge extended X-ray absorption fine structure...

SFVS is a powerful tool for quantitative measurement of protonated functional groups on mineral surfaces. We demonstrate this for the Corundum (1-102) interface where the orientation and nature of surface hydroxyls on the dry neutral surface can be obtained and compared with Crystal Truncation Rod (CTR) models for the surface termination and most l...

Ferrihydrite is an environmental iron oxyhydroxide mineral that is only found in the form of nanoscale particles yet exerts significant impacts on the biogeochemistry of soils, sediments and surface waters. This material has remained poorly characterized due to significant experimental challenges in determining stoichiometry and structure. In a bre...

The early development of nanoparticles at mineral-water interfaces exerts crucial influences on the sequestration and transport of aqueous toxic species originating from both natural and anthropogenic sources. Homogeneous and heterogeneous nucleation often occur simultaneously, making it difficult to sort out whether toxic species are transported a...

The reduction of ferric iron in solid phase minerals leads to the mobilization of ferrous iron in the environment and is thus a crucial component of the global iron cycle. Despite the importance of this process, a mechanistic understanding of the structural and chemical changes that are caused by this electron transfer reaction is not established b...

Goethite(α-FeOOH), an abundant and highly reactive iron oxyhydroxide mineral, has been the subject of numerous studies of environmental interface reactivity. However, such studies have been hampered by the lack of experimental constraints on aqueous interface structure, and especially of the surface water molecular arrangements. Structural informat...

The structure of nanoparticles is nonstationary and changes in response to the surface environment where the nanoparticles are situated. Nanoparticle-environment interaction determines the nature of the structure change, an important consideration for evaluating subsequent environmental impact. In this work, we used ZnS nanoparticles to interact wi...

The role of oligo-elements such as Zn in the genesis of pathological calcifications is widely debated in the literature. An essential element of discussion is given by their localisation either at the surface or within the Ca apatite crystalline network. To determine the localisation, X-ray absorption experiments have been performed at SOLEIL. The...

Synthetic analogs of naturally occurring nanoparticles have been studied by a range of X-ray techniques to determine their structure and chemistry, and relate these to their novel chemical properties and physical behavior. ZnS nanoparticles, formed in large concentrations naturally bymicrobial action, have an interesting core-shell structure with a...

Compared with macroscopic surfaces, the structure of water around nanoparticles is difficult to probe directly. We used molecular dynamics simulations to investigate the effects of particle size and morphology on the time-averaged structure and the dynamics of water molecules around two sizes of hematite (α-Fe2O3) nanoparticles. Interrogation of th...

Amorphous titania (TiOâ) is an important precursor for synthesis of single-phase nanocrystalline anatase. We synthesized amorphous titania by hydrolysis of titanium ethoxide at the ice point. Transmission electron microscopy examination and nitrogen gas adsorption indicated that the particle size of the synthesized titania is -2 nm. Synchrotron wid...

Nanoparticle properties can show marked departures from their bulk analog materials, including large differences in chemical reactivity, molecular and electronic structure, and mechanical behavior. The greatest changes are expected at the smallest sizes, e.g. 10 nanometers and less, where surface effects are likely to dominate bonding, shape, and e...

Ultrafine (2 - 3 nm) titania (TiO2) nanoparticles show only diffuse scattering by both conventional powder x-ray diffraction and electron diffraction. We used synchrotron wide-angle x-ray scattering (WAXS) to probe the atomic correlations in this amorphous material. The atomic pair-distribution function (PDF) derived from Fourier transform of the W...

This very first report of an X-ray absorption spectroscopy experiment at Synchrotron SOLEIL is part of a long-term study dedicated to pathological calcifications. Such biological entities composed of various inorganic and/or organic compounds also contain trace elements. In the case of urinary calculi, different papers already published have pointe...

Phase-sensitive sum-frequency vibrational spectroscopy was used to study water/vapor interfaces of HCl, HI, and NaOH solutions. The measured imaginary part of the surface spectral responses provided direct characterization of OH stretch vibrations and information about net polar orientations of water species contributing to different regions of the...

Sum-frequency vibrational spectroscopy in the OH stretch region was employed to study structures of water/alpha-Al2O3 (0001) interfaces at different pH values. Observed spectra indicate that protonation and deprotonation of the alumina surface dominate at low and high pH, respectively, with the interface positively and negatively charged accordingl...

The formation of any phase, whether natural or synthetic (Fig. 7.1), is usually a dis-equilibrium process that follows a series of steps until a thermodynamically stable state (equilibrium) is achieved. The first step in the process of creating a new solid phase from a supersaturated solution (either aqueous or solid) is called nucleation. A partic...

The unusual luminescence of particular varieties of natural pink calcite (CaCO3) samples was studied by laser-induced time-resolved luminescence spectroscopy at different temperatures. The luminescence is characterized by intense blue emission under shortwave UV lamp excitation with an extremely long decay time, accompanied by pink-orange luminesce...

The interaction of metal ions and oxyanions with nanoscale mineral phases has not been extensively studied despite the increased recognition of their prevalence in natural systems as a significant component of geomedia. A combination of macroscopic uptake studies to investigate the adsorption behavior of As(V), Cu(II), Hg(II), and Zn(II) onto nanop...

Arsenate and silicate are tetrahedral anions that strongly sorb to positive Fe oxide surfaces over the pH range 2–7. Both are important agents for modification of Fe oxide surface reactivity, and notably passivate against other sorption reactions. Arsenate is a significant health hazard as a sorbed pollutant associated with acid mine drainage, whil...

The adsorption of aqueous reductants to the surface of ferric iron bearing minerals and the subsequent creation and dissolution of ferrous iron are crucial steps in the geochemical cycling of this transition metal. While conceptual models of reductive dissolution are well established, the details of the interfacial electron transfer step are not we...

The nucleation and growth of metal oxide nanoparticles and films on mineral surfaces can markedly affect aqueous metal contaminant transport and other surface-controlled reactions. Recently, grazing incidence small angle x-ray scattering (GISAXS) has been used to analyze the size, shape, and distribution of quantum dots and polymers on substrates....

The interactions between water and mineral surfaces are crucial for stabilizing surface structures [1] and mediating interfacial adsorption reactions of aqueous ions [2]. Nanoscale minerals, such as the iron oxides, are extremely common natural products of biomineralization and chemical weathering reactions. Although frequently a minority fraction,...

The structure of the hydroxylated α-Fe2O3(11¯02) surface prepared via a wet chemical and mechanical polishing (CMP) procedure was determined using X-ray crystal truncation rod diffraction. The experimentally determined surface model was compared with theoretical structures developed from density functional theory (DFT) calculations to identify the...

Chemical reactions at the mineral and water interface play an important role in many natural and technological processes, from controlling the fate and transport of environmental contaminants, and biological availability and geochemical cycling of iron to the electronic device fabrications. The interface structure and composition of a mineral, dict...

Environmental nanoparticles are often poorly-crystalline or metastable structures, whose kinetics of formation and growth are poorly understood. Further, the sorption or growth of nanoparticles on mineral surfaces may control the mineral surface's reactivity and modify its ability to influence contaminant transport. Due to the characteristic length...

We present a phase-sensitive SFVS technique that captures both the magnitude and the phase of an interfacial vibrational spectrum and apply it to study water/vapor interfaces allowing unambiguous decomposition of OH stretch peaks.

Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continen...

This work examines the red luminescence of benitoite studied by laser-induced time-resolved luminescence spectroscopy. This method allows the differentiation between luminescence centers of similar emission wavelengths, but different decay times. We have also examined the luminescence intensity and decay time as a function of temperature. We found...

Nanoparticulate goethite, akaganeite, hematite, ferrihydrite and schwertmannite are important constituents of soils, sediments and mine drainage outflows. These minerals have high sorption capacities for metal and anionic contaminants such as arsenic, chromium, lead, mercury and selenium. Contaminant sequestration is accomplished mainly by surface...

X-ray diffraction [crystal-truncation-rod (CTR)] studies of the surface structure of moisture-equilibrated hematite reveal sites for complexation not present on the bulk oxygen-terminated surface, and impose constraints on the types of inner-sphere sorption topologies. We have used this improved model of the hematite surface to analyze grazing-inci...

The coordination environment of Fe(II) has been examined in seven anhydrous ferrosilicate glasses at 298 K and 1 bar using 57Fe Mössbauer, Fe K-edge X-ray near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS), UV-Vis-NIR, and magnetic circular dichroism (MCD) spectroscopies. Glasses of the following compositions were syn...

Evaluation of the long-term health risks of uranium contamination in soils, sediments, and groundwater requires a fundamental understanding of the various processes affecting subsurface transport of uranium, including adsorption processes at mineral/water interfaces. In this study, the sites of binding and surface complexation of U(VI) adsorbed on...

On October 20–26, 2004, more than 350 people participated in the 31st Annual Stanford Synchrotron Radiation Laboratory (SSRL) Users' Meeting, workshops, and social events. The presentation by SSRL Director Keith Hodgson in the opening session focused on the success in 2004 in getting SPEAR3 and the SSRL beam lines operating and productive. Looking...

Water structures at hydrophilic and hydrophobic interfaces are relevant to many problems in various disciplines. Sum-frequency vibrational spectroscopy (SFVS) is a unique technique to study such interfaces at the molecular level. We have developed a phase-sensitive SFVS method that provides both magnitude and phase of the nonlinear spectral respons...

A phase-sensitive sum-frequency vibrational spectroscopic technique is developed to study interfacial water structure of water/quartz interfaces. Measurements allow deduction of both real and imaginary parts of the surface nonlinear spectral response, revealing an unprecedentedly detailed picture of the net polar orientations of the water species a...

The structure of the hydroxylated hematite (0Â 0Â 0Â 1) surface was investigated using crystal truncation rod diffraction and density functional theory. The combined experimental and theoretical results suggest that the surface is dominated by two hydroxyl moieties--hydroxyls that are singly coordinated and doubly coordinated with Fe. The results a...

The phytoplankton assemblage at Ocean Station Papa (OSP) in the Subarctic Pacific in February 1996 was dominated by large chain forming diatoms and abundant coccolithophores. This phytoplankton assemblage is atypical of an HNLC region and strongly suggests a recent supply of bioavailable iron. Using synchrotron X-Ray Fluorescence (XRF) and Scanning...

Nanoparticles may contain unusual forms of structural disorder that can substantially modify materials properties and thus cannot solely be considered as small pieces of bulk material. We have developed a method to quantify intermediate-range order in 3.4-nanometer-diameter zinc sulfide nanoparticles and show that structural coherence is lost over...

It is proved that blue luminescence from benitoite is connected with intrinsic luminescence centers, namely isolated TiO6 octahedra. The metastable level 3T1u is the emitting level at low temperatures with a long decay time of 1.1 ms. At higher temperatures an energy level with higher radiation probability must be involved in the emission process,...

A room temperature solid-state structural transformation was observed in 3 nm ZnS nanoparticles in methanol following the addition of water (Zhang et al., Nature 424, 1025, 2003). Experimental wide angle x-ray scattering (WAXS), x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectroscopy measuremen...

Sum-frequency vibrational spectroscopy was used to assess water molecules ordering and orientation at the water/alpha-quartz interface. A special scheme allowed suppression of quartz bulk signal and measurement of the amplitude and phase of the nonlinear susceptibility

A new high‐precision spectrometer system has been developed and tested for measuring grazing‐incidence XAFS spectra, x‐ray reflectivity, and standing wave intensity data from adsorbates on oriented single crystals and flat polycrystalline samples. The instrument system was designed for routine, rapid installation and alignment in synchrotron experi...

Selected beam geometry allows us to suppress the bulk contribution to sum-frequency generation from crystalline quartz and use sum-frequency vibrational spectroscopy to study water/α-quartz interfaces with different bulk pH values. The spectra are qualitatively similar to those of water/fused-quartz interfaces, but display an ice-like peak that res...

Sum-frequency vibrational spectroscopy (SFVS) is a common tool for studies of surfaces and interfaces. So far, only the magnitude of the surface nonlinear susceptibility, i^(2)_S(ω = ω_vis+ω_IR), has been deduced from spectroscopic measurements, but not its phase, φ(ω). We present here a method that allows complete determination of i^(2)_S(ω) for a...

Sum-frequency vibrational spectroscopy was used to assess water molecules ordering and orientation at the water/alpha-quartz interface. A special scheme allowed suppression of quartz bulk signal and measurement of the amplitude and phase of the nonlinear susceptibility

Heightened biological activity was observed in February 1996in the high-nutrient low-chlorophyll (HNLC) subarctic North PacificOcean, a region that is thought to beiron-limited. Here we provideevidence supporting the hypothesis that Ocean Station Papa (OSP) in thesubarctic Pacific received a lateral supply of particulate iron from thecontinental ma...

If a natural geologic or biomineralized sample contained an unknown Fe mineral at the sub-micron level, could we unravel its nature with synchrotron spectromicroscopy? To address this question we analyzed 20 compounds and minerals containing Fe(II) and Fe(III) at the Fe L-edge with x-ray absorption near edge structure (XANES) spectroscopy. In addit...