Fe(III) (oxyhydr)oxide reduction by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens.

Some thermophilic bacteria from deep-sea hydrothermal vents grow by dissimilatory iron reduction, but our understanding of their biogenic mineral transformations is nascent. Mineral transformations catalyzed by the thermophilic iron-reducing bacterium Desulfovulcanus ferrireducens during growth at 55°C were examined using synthetic nanophase ferrihydrite, akaganeite, and lepidocrocite separately as terminal electron acceptors. Spectral analyses using visible-near infrared (VNIR), Fourier-transform infrared attenuated total reflectance (FTIR-ATR), and Mössbauer spectroscopies were complemented with x-ray diffraction (XRD) and transmission electron microscopy (TEM) using selected area electron diffraction (SAED) and energy dispersive X-ray (EDX) analyses. The most extensive biogenic mineral transformation occurred with ferrihydrite, which produced a magnetic, visibly dark mineral with spectral features matching cation-deficient magnetite. Desulfovulcanus ferrireducens also grew on akaganeite and lepidocrocite and produced non-magnetic, visibly dark minerals that were poorly soluble in the oxalate solution. Bioreduced mineral products from akaganeite and lepidocrocite reduction were almost entirely absorbed in the VNIR spectroscopy in contrast to both parent minerals and the abiotic controls. However, FTIR-ATR and Mössbauer spectra and XRD analyses of both biogenic minerals were almost identical to the parent and control minerals. The TEM of these biogenic minerals showed the presence of poorly crystalline iron nanospheres (50-200 nm in diameter) of unknown mineralogy that were likely coating the larger parent minerals and were absent from the controls. The study demonstrated that thermophilic bacteria transform different types of Fe(III) (oxyhydr)oxide minerals for growth with varying mineral products. These mineral products are likely formed through dissolution-reprecipitation reactions but are not easily predictable through chemical equilibrium reactions alone.

Surface Site Density of Synthetic Goethites and Its Relationship to Atomic Surface Roughness and Crystal Size.

The capacity for crystals to adsorb elements and molecules is a function of the structures of their crystal faces and the relative proportions of those faces. More importantly, this study shows that the surface structure of crystal faces is affected by their surface roughness and is the dominant factor controlling the absorption site density. In a continuation of the study of synthetic goethites with varying single crystal size distributions, two more synthetic goethites with intermediate sizes were analyzed by Brunauer-Emmett-Teller (BET) and atomic-resolution scanning transmission electron microscopy (STEM) to determine the effects of crystal size on their shape, atomic-scale surface roughness, and ultimately on their total surface site density. Results show that surface roughness scales directly with the size [or inversely with the specific surface area (SSA)] of synthetic goethites in the SSA range of 40-75 m2/g. This surface roughness, in turn, increases the total site density over ideal atomically smooth crystals. The total site density of synthetic goethite increases from a combination of decreasing crystal length/width ratio and increasing surface roughness.

Depth sequence distribution of water extractable colloidal phosphorus and its phosphorus speciation in intensively managed agricultural soils.

Legacy phosphorus (P) has accelerated the subsurface transport of colloidal P (CP) in intensively managed agricultural soils in the Midwestern U.S. Because of its high P sorption capacity and mobility, understanding the depth sequence distribution of mobile CP and its speciation in the soil profile is critical in assessing total P (TP) loss to protect the water quality of adjacent water bodies. In this study, physicochemical properties of water-extractable colloids (WECs) from the soil profile at 0-180 cm were characterized using conventional wet chemical analysis. Solution P-31 nuclear magnetic resonance spectroscopy (NMR), P and Fe K-edge X-ray absorption spectroscopy, and transmission electron microscopy were also used to understand P speciation and mineralogy of CP. Percent recovery of WECs per bulk soil increased more than three times with increasing depth. Considering mildly alkaline pH of pore water and negative zeta potential (-21 ± 4 mV) of WECs (size: 1.65 ± 0.45 µm), the transport of P rich WECs (TP: approximately 210-700 mg kg-1) were facilitated from surface to subsoils. Generally, TP in WEC decreased with increasing depth. Interestingly, WECs in subsoil contain organic P (OP) as much as 60 mg kg-1. NMR analysis clearly showed the presence of OP monoesters, OP diesters, and orthophosphate in these particles. Both orthophosphate and OP species interacted with iron oxyhydroxides, calcite, and aluminol functional groups of gibbsite and or phyllosilicates. The study showed the availability of WECs from surface to subsoils that carry orthophosphate as well as OP in legacy P impacted agricultural soils in the Midwestern U.S.

Maximized Hole Trapping in a Polystyrene Transistor Dielectric from a Highly Branched Iminobis(aminoarene) Side Chain.

We synthesized highly branched and electron-donating side chain subunits and attached them to polystyrene (PS) used as a dielectric layer in a pentacene field-effect transistor. The influence of these groups on dielectric function, charge retention, and threshold voltage shifts (ΔVth) depending on their positions in dielectric multilayers was determined. We compared the observations made on an N-perphenylated iminobisaniline side chain with those from the same side chains modified with ZnO nanoparticles and with an adduct formed from tetracyanoethylene (TCNE). We also synthesized an analogue in which six methoxy groups are present instead of two amine nitrogens. At 6 mol % side chain, hopping transport was sufficient to cause shorting of the gate, while at 2 mol %, charge trapping was observable as transistor threshold voltage shifts (ΔVth). We created three types of devices: with the substituted PS layer as single-layer dielectric, on top of a cross-linked PS layer but in contact with the pentacene (bilayers), and sandwiched between two PS layers in trilayers. Especially large bias stress effects and ΔVth, larger than those in the case of the hexamethoxy and previously studied dimethoxy analogues, were observed in the second case, and the effects increased with the increasing electron-donating properties of the modified side chains. The highest ΔVth was consistent with a majority of the side chains stabilizing the trapped charge. Trilayer devices showed decreased charge storage capability compared to previous work in which we used less donating side chains but in higher concentrations. The ZnO and TCNE modifications resulted in slightly more and less negative ΔVth, respectively, when the side chain polystyrene was not in contact with the pentacene and isolated from the gate electrode. The results indicate a likely maximum combination of molecular charge stabilizing activity and side chain concentration that still allows gate dielectric function.

In situ magnetic identification of giant, needle-shaped magnetofossils in Paleocene-Eocene Thermal Maximum sediments.

Near-shore marine sediments deposited during the Paleocene-Eocene Thermal Maximum at Wilson Lake, NJ, contain abundant conventional and giant magnetofossils. We find that giant, needle-shaped magnetofossils from Wilson Lake produce distinct magnetic signatures in low-noise, high-resolution first-order reversal curve (FORC) measurements. These magnetic measurements on bulk sediment samples identify the presence of giant, needle-shaped magnetofossils. Our results are supported by micromagnetic simulations of giant needle morphologies measured from transmission electron micrographs of magnetic extracts from Wilson Lake sediments. These simulations underscore the single-domain characteristics and the large magnetic coercivity associated with the extreme crystal elongation of giant needles. Giant magnetofossils have so far only been identified in sediments deposited during global hyperthermal events and therefore may serve as magnetic biomarkers of environmental disturbances. Our results show that FORC measurements are a nondestructive method for identifying giant magnetofossil assemblages in bulk sediments, which will help test their ecology and significance with respect to environmental change.

High flow event induced the subsurface transport of particulate phosphorus and its speciation in agricultural tile drainage system.

Subsurface storm flow of phosphorus (P), including particulate P, has been recently discussed as an important P transport path in contrast to typical surface runoff events. However, P speciation, and P concentration during storm events has not been extensively investigated; therefore, its contribution to the water quality is not clearly understood. In this study, the physicochemical properties of particulate P in tile water samples during a high flow event were investigated in Midwestern agricultural lands using wet chemical methods, 31P Nuclear Magnetic Resonance spectroscopy and P K-edge X-ray absorptions near edge structure spectroscopy. In slightly alkaline pH tile water, total P was ranging from ∼0.06 to 0.22 mg L-1, which is significantly greater than dissolved reactive P (DRP) (∼0.02-0.08 mg L-1). The tile water contains P enriched particulate matters (∼200-660 mg L-1). Total P in the colloidal fraction was from 1013 to 2270 mg kg-1. Phosphate and organic P species, especially monoesters, are sorbed in soil colloids like calcite, and iron oxides, and colloids are effective carriers of P in the subsurface transport process during storm events. The results of this study show that storm events can accelerate the subsurface transport of P with soil particles in addition to DRP.

Nano-folded Gold Catalysts for Electroreduction of Carbon Dioxide.

The local structure and geometry of catalytic interfaces can influence the selectivity of chemical reactions. Selectivity is often critical for the practical realization of reactions such as the electroreduction of carbon dioxide (CO2). Previously developed strategies to manipulate the structure and geometry of catalysts for electroreduction of CO2 involve complex processes or fail to efficiently alter the selectivity. Here, using a prestrained polymer, we uniaxially and biaxially compress a 60 nm gold film to form a nano-folded electrocatalyst for CO2 reduction. We observe two kinds of folds and can tune the ratio of loose to tight folds by varying the extent of prestrain in the polymer. We characterize the nano-folded catalysts using X-ray diffraction, scanning, and transmission electron microscopy. We observe grain reorientation and coarsening in the nano-folded gold catalysts. We measure an enhancement of Faradaic efficiency for carbon monoxide formation with the biaxially compressed nano-folded catalyst by a factor of about nine as compared to the flat catalyst (up to 87.4%). We rationalize this observation by noting that an increase of the local pH in the tight folds of the catalyst outweighs the effects of alterations in grain characteristics. Together, our studies demonstrate that nano-folded geometries can significantly alter grain characteristics, mass transport, and catalytic performance.

Ordered Intermetallic Pd3Bi Prepared by an Electrochemically Induced Phase Transformation for Oxygen Reduction Electrocatalysis.

The synthesis of alloys with long-range atomic-scale ordering (ordered intermetallics) is an emerging field of nanochemistry. Ordered intermetallic nanoparticles are useful for a wide variety of applications such as catalysis, superconductors, and magnetic devices. However, the preparation of nanostructured ordered intermetallics is challenging in comparison to disordered alloys, hindering progress in material development. Herein, we report a process for converting colloidally synthesized ordered intermetallic PdBi2 to ordered intermetallic Pd3Bi nanoparticles under ambient conditions by electrochemical dealloying. The low melting point of PdBi2 corresponds to low vacancy formation energies, which enables the facile removal of the Bi from the surface while simultaneously enabling interdiffusion of the constituent atoms via a vacancy diffusion mechanism under ambient conditions. The resulting phase-converted ordered intermetallic Pd3Bi exhibits 11 times and 3.5 times higher mass activity and high methanol tolerance for the oxygen reduction reaction compared with Pt/C and Pd/C, respectively, which is the highest reported for a Pd-based catalyst, to the best of our knowledge. These results establish a key development in the synthesis of noble-metal-rich ordered intermetallic phases with high catalytic activity and set forth guidelines for the design of ordered intermetallic compounds under ambient conditions.

Crystal Face Distributions and Surface Site Densities of Two Synthetic Goethites: Implications for Adsorption Capacities as a Function of Particle Size.

Two synthetic goethites of varying crystal size distributions were analyzed by BET, conventional TEM, cryo-TEM, atomic resolution STEM and HRTEM, and electron tomography in order to determine the effects of crystal size, shape, and atomic scale surface roughness on their adsorption capacities. The two samples were determined by BET to have very different site densities based on CrVI adsorption experiments. Model specific surface areas generated from TEM observations showed that, based on size and shape, there should be little difference in their adsorption capacities. Electron tomography revealed that both samples crystallized with an asymmetric {101} tablet habit. STEM and HRTEM images showed a significant increase in atomic-scale surface roughness of the larger goethite. This difference in roughness was quantified based on measurements of relative abundances of crystal faces {101} and {201} for the two goethites, and a reactive surface site density was calculated for each goethite. Singly coordinated sites on face {210} are 2.5 more dense than on face {101}, and the larger goethite showed an average total of 36% {210} as compared to 14% for the smaller goethite. This difference explains the considerably larger adsorption capacitiy of the larger goethite vs the smaller sample and points toward the necessity of knowing the atomic scale surface structure in predicting mineral adsorption processes.