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Synthesis and characterization of poorly-crystaline Fe-Al nano-hydroxides

Synthesis and characterization of poorly-crystaline Fe-Al nano-hydroxides. Katya Bazilevskaya, Douglas Archibald, Carmen Enid Martínez. Crop and Soil Sciences Department & Center of Environmental Kinetics Analysis The Pennsylvania State University.

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Synthesis and characterization of poorly-crystaline Fe-Al nano-hydroxides

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  1. Synthesis and characterization of poorly-crystaline Fe-Al nano-hydroxides Katya Bazilevskaya, Douglas Archibald, Carmen Enid Martínez Crop and Soil Sciences Department & Center of Environmental Kinetics Analysis The Pennsylvania State University 18th World Congress of Soil Science July 11, 2006

  2. Why we study hydroxide nano-particles? • Have large reactive surface area • Create pH-dependent charge Form coatings: meta-stable mixtures of Fe-, Al- and Si oxides and organics, which: • Affect mobility of nutrients and contaminants • Reflect soil-forming processes • Affect mineral dissolution rates

  3. Experimental conditions: [Fe+Al] = 10 mM; %Al: 0, 10, 25, 30, 50, 75, 100; pH = 5 0.1 M KOH Fe (+Al) nitrate sol-n, pH ~2 • Slow titration rate (0.1 ml/min) • Dyalisis to remove salts and excess Al

  4. Measured by light scattering (ZetaPALS, Brookhaven Instruments) AFM images of Fe-Al particles 0% Al 30% Al

  5. What methods to use? X-ray diffraction (XRD): • long range order information • synchrotron XRD for poorly crystalline hydroxides • only crystalline phase Extended X-ray Absorption Fine structure spectroscopy (EXAFS) • short range order (atom’s second neighbor information – bond distance, type of bond)) • both crystalline and amorphous • Can only probe for Fe, not Al Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR FTIR) • short range order (bonding and reactivity of protons) • both crystalline and amorphous • distinct iron and Al hydroxide OH-vibrations • ATR technique provide precise technique: measures nano-particles coatings on the sensor (do not need to separate nano-particles by centrifugation and freeze-drying)

  6. Structure of end-members Goethite Gibbsite Goethite 3450, 3206 1687, 1643 888, 798 Gibbsite 3620, 3525 3455, 3390 1024, 975 -

  7. %Al increases %Al increases Infrared spectra of Fe-Al hydroxides with different %Al 0% Al 100% Al

  8. Change of infrared spectra of Fe-Al hydroxides with time 0%Al 25%Al Time = 0 days Time = 2 days @ 50 C

  9. Fe-only Fe-O Fe-Fe Fourier Transformed XAFS, χ (R) Fe:Al=1:1 Fe-Al Distance to neighboring atom R, Å Preliminary Fe-EXAFS data(aged for 2 weeks) From the Literature • Fe-Fe distances for • goethite • 3.0 – 3.4 Å • (2.5-2.9 in R) • Fe-Al distances for • Fe3+-gibbsite • 2.9 Å (2.4 in R) • Epidote • 2.95 Å (2.5 in R) • LiAlO2with 1wt.%Fe3+ • 3.15 Å (2.6 in R) Radial distribution functions for oxide suspensions of various Fe:Al ratios

  10. Connection with real life….Spodosols Profile-view Top-view • To monitor formation of iron coatings on quartz in situ: • placed quartz in the soil profile • recovered after 1 year

  11. Acknowledgments • Funding: Center of Environmental Kinetics analysis (CEKA) • XRD and EXAFS: beamlines X-16C, X-18B, X-10C, National Synchrotron Light Source, Brookhaven National Laboratory • ….

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