Quantifying the distribution of nanodiamonds in pre-Younger Dryas to recent age deposits along Bull Creek, Oklahoma panhandle, USA.

High levels of nanodiamonds (nds) have been used to support the transformative hypothesis that an extraterrestrial (ET) event (comet explosion) triggered Younger Dryas changes in temperature, flora and fauna assemblages, and human adaptations [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 104(41):16016-16021]. We evaluate this hypothesis by establishing the distribution of nds within the Bull Creek drainage of the Beaver River basin in the Oklahoma panhandle. The earlier report of an abundance spike of nds in the Bull Creek I Younger Dryas boundary soil is confirmed, although no pure cubic diamonds were identified. The lack of hexagonal nds suggests Bull Creek I is not near any impact site. Potential hexagonal nds at Bull Creek were found to be more consistent with graphene/graphane. An additional nd spike is found in deposits of late Holocene through the modern age, indicating nds are not unique to the Younger Dryas boundary. Nd distributions do not correlate with depositional environment, pedogenesis, climate perturbations, periods of surface stability, or cultural activity.

Using chromate to investigate the impact of natural organics on the surface reactivity of nanoparticulate magnetite.

Chromate was used as a chemical probe to investigate the size-dependent influence of organics on nanoparticle surface reactivity. Magnetite-chromate sorption experiments were conducted with ∼ 90 and ∼ 6 nm magnetite nanoparticles in the presence and absence of fulvic acid (FA), natural organic matter (NOM), and isolated landfill leachate (LL). Results indicated that low concentrations (1 mg/L) of organics had no noticeable impact on chromate sorption, whereas concentrations of 50 mg/L or more resulted in decreased amounts of chromate sorption. The adsorption of organics onto the magnetite surfaces interfered equally with the ability of the 6 and 90 nm particles to sorb chromate from solution, despite the greater surface area of the smaller particles. Results indicate the presence of organics did not impact the redox chemistry of the magnetite-chromate system over the duration of the experiments (8 h), nor did the organics interact with the chromate in solution. Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) results indicate that the organics blocked the surface reactivity by occupying surface sites on the particles. The similarity of results with FA and NOM suggests that coverage of the reactive mineral surface is the main factor behind the inhibition of surface reactivity in the presence of organics.

Size-dependent reactivity of magnetite nanoparticles: a field-laboratory comparison.

Logistic challenges make direct comparisons between laboratory- and field-based investigations into the size-dependent reactivity of nanomaterials difficult. This investigation sought to compare the size-dependent reactivity of nanoparticles in a field setting to a laboratory analog using the specific example of magnetite dissolution. Synthetic magnetite nanoparticles of three size intervals, ∼ 6 nm, ∼ 44 nm, and ∼ 90 nm were emplaced in the subsurface of the USGS research site at the Norman Landfill for up to 30 days using custom-made subsurface nanoparticle holders. Laboratory analog dissolution experiments were conducted using synthetic groundwater. Reaction products were analyzed via TEM and SEM and compared to initial particle characterizations. Field results indicated that an organic coating developed on the particle surfaces largely inhibiting reactivity. Limited dissolution occurred, with the amount of dissolution decreasing as particle size decreased. Conversely, the laboratory analogs without organics revealed greater dissolution of the smaller particles. These results showed that the presence of dissolved organics led to a nearly complete reversal in the size-dependent reactivity trends displayed between the field and laboratory experiments indicating that size-dependent trends observed in laboratory investigations may not be relevant in organic-rich natural systems.

A2P2S6 (A = Ba and Pb): a good platform to study the polymorph effect and lone pair effect to form an acentric structure.

Three ternary thiophosphates α-Ba2P2S6, ß-Ba2P2S6, and Pb2P2S6 were synthesized via a high temperature salt flux method or an I2 transport reaction. ß-Ba2P2S6 and Pb2P2S6 were previously structurally characterized without investigating their optical properties. α-Ba2P2S6 was discovered for the first time, and it is isostructural to Pb2P2S6 and crystallizes in the acentric space group Pn (no. 7). ß-Ba2P2S6 crystallizes in the centrosymmetric space group P21/n (no. 14). There is a high structural similarity between α-Ba2P2S6, ß-Ba2P2S6, and Pb2P2S6 including close unit cell parameters and identical [P2S6] motifs. The structural relationships between α-Ba2P2S6 and ß-Ba2P2S6, and ß-Ba2P2S6 and Pb2P2S6 were elucidated by single crystal X-ray diffraction, differential scanning calorimetry (DSC), electronic structure calculations, and nonlinear optical property measurements. There are no phase transitions detected between α-Ba2P2S6 and ß-Ba2P2S6. From centrosymmetric ß-Ba2P2S6 to acentric Pb2P2S6, the chemical characteristics of Pb, such as stereoactive lone pairs, play a key role in the structural difference. Pb2P2S6 is uncovered as a type-I phase-matching material with a moderate second harmonic generation (SHG) response of 1.4 × AgGaS2 and a high laser damage threshold (LDT) of 2.5 × AgGaS2. α-Ba2P2S6 is not a type-I phase-matching material with a moderate second harmonic generation response (1.7 × AgGaS2, a sample of 225 µm particle size) and a high laser damage threshold (5.5 × AgGaS2).

Dissolution of Mn-bearing dolomite drives elevated Cr(VI) occurrence in a Permian redbed aquifer.

Municipalities in central Oklahoma, U.S.A. increasingly rely on water drawn from the Central Oklahoma Aquifer (COA) as surface water resources have not grown in proportion to population and current water demands. However, water drawn from certain regions of the COA frequently contains elevated levels of naturally occurring hexavalent chromium. Rock samples from the Norman Arsenic Test Hole Core (NATHC) were investigated to identify the mineralogic host(s) of Cr and mechanisms of Cr(VI) release via bulk mineralogy and chemistry measurements, selective chemical extractions, and microscale elemental analyses. Results demonstrate most COA Cr is contained in Fe oxides and clays as isomorphic substitutions for Fe(III). Analyses of regional groundwater data, including hierarchical clustering methods and GIS, demonstrate the most intense Cr(VI) occurrence is linked to cation exchange with Na-clays at depth. Cation exchange allows dissolution of Mn-bearing dolomite, which in turn produces Mn oxides in otherwise dolomite-saturated groundwaters. Mn oxides in turn are known to oxidize Cr(III) to Cr(VI). In general, co-occurrence of Mn-bearing carbonates and exchangeable clays in any aquifer, particularly those with Cr(III) present in iron oxide cements, serve as ingredients for groundwater occurrences of oxidizable trace metals.

Using chromate to investigate the impact of mineral-organic contact time on the surface reactivity of goethite.

Chromate was used as a chemical probe to investigate the impact of mineral-organic contact time on the surface reactivity of two different sizes of goethite particles. A series of goethite-chromate sorption batch reactions were conducted in the presence and absence of Suwannee River humic acid (HA) and natural organic matter (NOM) using nano- and micro-scale goethite particles. In experiments with added organics the amount of time allowed for goethite-organic matter interaction (i.e. contact time) was varied from less than 1 minute, up to 24 hours prior to the addition of chromate. Results indicated that nano- and micro-scale goethite in the absence of organics sorbed nearly identical amounts of chromate on a per mass basis, despite the greater surface area of the smaller particles. Results also indicated that the presence of ∼10 mg L-1 of HA and a contact time of less than 1 minute reduced the amount of chromate sorbed by both nano- and micro-scale goethite. Increasing the contact time resulted in greater decreases in chromate sorption. Experiments using NOM produced similar results. While chromate sorption was most rapid during the first hour of the experiments, goethite particles continued to sorb additional chromate over a period of up to 7 days. Additionally, a noticeable impact on chromate sorption due to increased contact time was present over that time period.

Thermal, Electrical and Surface Hydrophobic Properties of Electrospun Polyacrylonitrile Nanofibers for Structural Health Monitoring.

This paper presents an idea of using carbonized electrospun Polyacrylonitrile (PAN) fibers as a sensor material in a structural health monitoring (SHM) system. The electrospun PAN fibers are lightweight, less costly and do not interfere with the functioning of infrastructure. This study deals with the fabrication of PAN-based nanofibers via electrospinning followed by stabilization and carbonization in order to remove all non-carbonaceous material and ensure pure carbon fibers as the resulting material. Electrochemical impedance spectroscopy was used to determine the ionic conductivity of PAN fibers. The X-ray diffraction study showed that the repeated peaks near 42° on the activated nanofiber film were α and ß phases, respectively, with crystalline forms. Contact angle, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were also employed to examine the surface, thermal and chemical properties of the carbonized electrospun PAN fibers. The test results indicated that the carbonized PAN nanofibers have superior physical properties, which may be useful for structural health monitoring (SHM) applications in different industries.