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Magnetic properties of synthetic six-line ferrihydrite ..

Synthesis, Characterization and Application of 2-Line and 6-Line Ferrihydrite to Pb(II) Removal from Aqueous Solution

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properties of synthetic 6-line ferrihydrite ..

Therefore, the main objective of this study was to examine the effect of silicic acid on the extent and molecular mechanisms of both arsenate and arsenite adsorption to a model Fe(III) oxyhydroxide (ferrihydrite, Fe5HO8•4H2O). Ferrihydrite was chosen because it is commonly employed as an adsorbent for arsenic removal during drinking water treatment () and it is also one of the most common naturally occurring Fe oxyhydroxides that can precipitate from many types of ferriferous solutions at the Earth’s surface (). This poorly crystalline mineral phase often has high specific surface area and reactive hydroxyl group site density, both of which make it a high affinity adsorbent for trace metal(loid) contaminants (; ). The in-situ molecular spectroscopic techniques of attenuated reflectance-Fourier transform infrared (ATR-FTIR) and extended X-ray absorption fine structure (EXAFS) were combined with batch adsorption methods to elucidate the effect of silicic acid on arsenic adsorption mechanisms at ferrihydrite surfaces across a gradient in pH that is representative of natural waters. The results of the batch experiments and spectroscopic analyses were further analyzed using density functional theory (DFT) modeling to quantify the bond energies associated with the spectroscopic indications of surface speciation of As(III), As(V) and Si(OH)4 and their complexation modes at ferrihydrite surfaces.

Synthetic nanocrystalline “6-line” ferrihydrite was recently studied through methods based ..
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, , , , and (2011)Ambient temperature synthesis of nanorod 6-line ferrihydrite and its cation sorption behavior. Toxicological & Environmental Chemistry, 93 (5). pp. 844-859.

Novel Synthesis and Structural Analysis of ..

The influence of silicate on transformation pathways of synthetic 2-line ferrihydrite.
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This poorly crystalline phase is suggested to impact the mobility of metal(loid)s through sorption reactions, and to provide an important source of bioavailable Fe primarily as a result of its high reactivity and high surface area, although this role is now being re-examined ( Ekstrom et al., 2010 ).

Six-line ferrihydrite was synthesized using the method of . Briefly, 250 mL of 0.48 M NaHCO3 (99.9%, Mallinckrodt) was added to an equal volume of 0.4 M Fe(NO3)3•9H2O (JB Baker, 98.8%) using a peristaltic pump during vigorous stirring over 120 min. Once the addition of NaHCO3 solution was complete, the suspension was microwave-annealed at 40 s intervals until it boiled to improve homogeneity of the nanoparticulate suspension. Immediately after heating, the suspension was plunged into an ice bath, brought to room temperature, and then transferred into dialysis tubing (Spectra/Por 7, 1000 MWCO) and dialyzed against NP water at 4 °C for 3 d, with dialysis water changed three times per day. A portion of the ferrihydrite colloidal suspension was freeze-dried and gently ground using an agate mortar and pestle for characterization, analysis and batch adsorption experiments. The remainder of the suspension was transferred to a polyethylene bottle and stored at 4 °C for spectroscopic studies. The ferrihydrite suspension was used within 3 weeks from synthesis in the experiments.

SYNTHESIS OF FERRIHYDRITE AND FEROXYHYTE

the purported "2-line" and "6-line" forms of ferrihydrite, ..
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All spectra were acquired at room temperature with 4.0 cm−1 resolution with 400 scans over the spectral range of 4000 – 600 cm−1 using the autogain function and aperture set at 100. For each experiment, background solution (i.e., 1 mM NaCl) was first pumped through the ATR cell, allowing the ferrihydrite coating to equilibrate at a given pH. The final background spectrum was collected when no further changes in the spectra were observed. Then, 1.0 mM arsenic solution in the absence or presence of 1.0 mM Si(OH)4 was injected into the cell to initiate the adsorption experiment. Spectra were collected as a function of pH (3.0 – 10.0) and reaction time at 15 min intervals until adsorption equilibrium was reached as indicated by no furthers changes between successive spectra. The pH of the solution in the reaction vessel was monitored throughout the measurement, and adjusted as necessary by addition of 10 mM NaOH or HCl. A final sample spectrum was obtained by subtracting the appropriate background spectrum (e.g., 1.0 mM NaCl, 1.0 mM Si(OH)4) from the sample spectrum. All data collection and spectral processing, including background subtraction and baseline correction, were performed using the OMNIC program (Thermo Nicolet, Co.).

Batch adsorption for As(III) on 6-L ferrihydrite were performed as described above for As(V) but with the following modifications. Since previous studies reported that arsenite associated with Fe and Mn oxyhydroxides in aqueous systems can be oxidized to arsenate by photolytically produced free radicals (), specific precautions were employed to prevent this reaction. All polyethylene centrifuge tubes containing sorbent suspensions were immediately flushed with N2 gas and sealed to prevent atmospheric exposure, and all were wrapped in aluminum foil to prevent photochemical oxidation during the adsorption experiments. The samples were equilibrated, centrifuged, and filtered as described above. Immediately after filtration, 100 μL of 0.15 M ethylenediaminetetraacetic acid (EDTA) solution was spiked into the filtrate as a preservative to stabilize As speciation (). An aliquot of the preserved filtrate was analyzed for total As, Si and Fe concentrations using ICP-MS within 24 h from the batch experiment. In addition, aqueous As speciation analysis was performed to confirm the efficacy of the preservation techniques using an HPLC equipped with an anion exchange column to separate the arsenic species prior to on-line injection to ICP-MS. Prior to the speciation analysis, the preserved filtrate was diluted with 50 mM (NH4)2CO3 (HPLC mobile phase). Wet pastes were kept frozen before As solid-state speciation analysis using As-XANES and EXAFS spectroscopy at the Stanford Synchrotron Radiation Lightsource (SSRL).

07/08/2016 · The peroxidase-like catalytic properties of 2-line ferrihydrite ..
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  • prepared under three different synthesis ..

    TRANSFORMATION OF 2-LINE FERRIHYDRITE ference between 2-line ferrihydrite and 6-line ferrihydrite is the ..

  • 2 line ferrihydrite synthesis essay - …

    23/01/2002 · Raman and infrared spectra of 2-line and 6-line ferrihydrite and schwertmannite ..

  • synthetic 2-line ferrihydrite, ..

    Synthesis of six-line ferrihydrite – 4 nm dots (4nm-6LF) The synthesis method was adapted from Burleson and Penn

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PDF Downloads : Oriental Journal of Chemistry

The synthesis of the nanorods began by using the 4 nm-6LF synthesis procedure (Sec. II A). After dialysis, the pH of the ferrihydrite suspension was quickly adjusted to 12 using 5 M NaOH (Fisher, ACS grade). A deep maroon suspension formed. The suspension was heated at 90°C for 24 h, after which a deep orange precipitate had settled to the bottom quarter of the bottle. The supernatant was discarded, and the remaining suspension was placed into dialysis bags, which were placed in Milli-Q H2O. The water was changed three times per day for three days. The resulting suspension was dried and ground as described above.

Journal of the American Chemical Society (ACS …

Iron oxides and oxyhydroxides are common and important materials in the environment, and they strongly impact the biogeochemical cycle of iron and other species at the Earth's surface. These materials commonly occur as nanoparticles in the 3–10 nm size range. This paper presents quantitative results demonstrating that iron oxide reactivity is particle size dependent. The rate and extent of the reductive dissolution of iron oxyhydroxide nanoparticles by hydroquinone in batch experiments were measured as a function of particle identity, particle loading, and hydroquinone concentration. Rates were normalized to surface areas determined by both transmission electron microscopy and Braunauer-Emmett-Teller surface. Results show that surface-area-normalized rates of reductive dissolution are fastest (by as much as 100 times) in experiments using six-line ferrihydrite versus goethite. Furthermore, the surface-area-normalized rates for 4 nm ferrihydrite nanoparticles are up to 20 times faster than the rates for 6 nm ferrihydrite nanoparticles, and the surface-area-normalized rates for 5 × 64 nm goethite nanoparticles are up to two times faster than the rates for 22 × 367 nm goethite nanoparticles.

Clare Grey - Stony Brook University

The X-ray diffraction (XRD) pattern of the synthetic material collected at Stanford Synchrotron Radiation Lightsource (SSRL) on beamline 11-3 shows 6 broad peaks, indicating its poor crystallinity (see ). Peak positions and intensities are in good agreement with the XRD pattern for 6-line ferrihydrite (). Specific surface area was calculated in accordance with BET theory using N2 adsorption data obtained at 77 K on a Beckman Coulter SA 3100 Gas Adsorption Surface Area Analyzer (Beckman Coulter Inc., Fullerton, CA). The result indicated that the synthetic 6-L ferrihydrite had a specific surface area of 311 ± 1.2 m2 g−1.

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