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

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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

18th World Congress of Soil Science July 11, 2006


Synthesis and characterization of poorly crystaline fe al nano hydroxides

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


Synthesis and characterization of poorly crystaline fe al nano hydroxides

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


Synthesis and characterization of poorly crystaline fe al nano hydroxides

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?

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)


Synthesis and characterization of poorly crystaline fe al nano hydroxides

Structure of end-members

Goethite

Gibbsite

Goethite 3450, 3206 1687, 1643 888, 798

Gibbsite 3620, 3525 3455, 3390 1024, 975 -


Synthesis and characterization of poorly crystaline fe al nano hydroxides

%Al increases

%Al increases

Infrared spectra of Fe-Al hydroxides with different %Al

0% Al

100% Al


Synthesis and characterization of poorly crystaline fe al nano hydroxides

Change of infrared spectra of Fe-Al hydroxides with time

0%Al

25%Al

Time = 0 days

Time = 2 days @ 50 C


Synthesis and characterization of poorly crystaline fe al nano hydroxides

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


Synthesis and characterization of poorly crystaline fe al nano hydroxides

Connection with real life….Spodosols

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

  • placed quartz in the soil profile

  • recovered after 1 year


Acknowledgments

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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