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

2. Why we study hydroxide nano-particles? 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  Have large reactive surface area  Create pH- dependent charge

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

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

6. 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)

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

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

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

10. Preliminary Fe-EXAFS data (aged for 2 weeks) Radial distribution functions for oxide suspensions of various Fe:Al ratios Fe-Fe distances for goethite 3.0 – 3.4 Å (2.5-2.9 in R) Fe-Al distances for Fe 3+ -gibbsite 2.9 Å (2.4 in R) Epidote 2.95 Å (2.5 in R) LiAlO 2 with 1wt.%Fe 3+ 3.15 Å (2.6 in R) From the Literature Fourier Transformed XAFS, χ (R) Fe-OFe-Fe Fe-Al Fe-only Fe:Al=1:1 Distance to neighboring atom R, Å

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

12. 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  ….