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
18th World Congress of Soil Science July 11, 2006
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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

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

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Structure of end-members
Goethite
Gibbsite
n (OH) stretching (OH) bending (OH) deformation
Goethite 3450, 3206 1687,
1643 888, 798 Gibbsite 3620, 3525 3455,
3390 1024, 975 -

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Infrared spectra of Fe-Al hydroxides with
different Al
0 Al
100 Al
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Change of infrared spectra of Fe-Al hydroxides
with time
0Al
25Al
Time 0 days
Time 2 days _at_ 50 C
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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)
• LiAlO2 with 1wt.Fe3
• 3.15 Å (2.6 in R)

Radial distribution functions for oxide
suspensions of various FeAl ratios
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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

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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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