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

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


Why we study hydroxide nano-particles? nano-hydroxides

  • 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


Experimental conditions: nano-hydroxides

[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


Measured by light scattering (ZetaPALS, Brookhaven Instruments)

AFM images of Fe-Al particles

0% Al

30% Al


What methods to use
What methods to use? Instruments)

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)


Structure of end-members Instruments)

Goethite

Gibbsite

Goethite 3450, 3206 1687, 1643 888, 798

Gibbsite 3620, 3525 3455, 3390 1024, 975 -


%Al increases Instruments)

%Al increases

Infrared spectra of Fe-Al hydroxides with different %Al

0% Al

100% Al


Change of infrared spectra of Fe-Al hydroxides with time Instruments)

0%Al

25%Al

Time = 0 days

Time = 2 days @ 50 C


Fe-only Instruments)

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


Connection with real life….Spodosols Instruments)

Profile-view

Top-view

  • To monitor formation of iron coatings on quartz in situ:

  • placed quartz in the soil profile

  • recovered after 1 year


Acknowledgments
Acknowledgments Instruments)

  • 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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