1. A Thesis Proposal by Katya Bazilevskaya Department of Crop and Soil Sciences The Pennsylvania State University November 5, 2006 Advisor: Carmen Enid Martinez Mixed Fe-Al hydroxide nano-particles: precipitation and transformation in solution and on quartz surface

2. Center of Environmental Kinetic Analysis (CEKA): What factors control the nucleation, growth, and transformation of mixed Fe-, Al-, and Si- oxides from solution (homogeneous) and on mineral surfaces (heterogeneous)? Low-crystalline Fe and Al hydroxides exist as colloidal (<0.1 µm size) particles in natural waters or as coatings on the soil minerals Have strong ability to adsorb contaminants due to their high surface area and pH-dependent surface charge. Rationale From Penn et al. (2001) Better understanding of crystallization pathways is needed to formulate rate models for soil environments and to improve remediation techniques This research is developing new approaches and techniques to study composition and transformations of mixed Fe-Al hydroxide nano-colloids

3. Research Hypotheses In nano-colloidal system: Mixed Fe-Al hydroxides have slower crystallization rate than the pure phases Two main factors that dictate the rate of crystallization of mixed Fe-Al hydroxides are time and chemical composition (Fe/Al ratio); Crystallization pathways can produce a variety of intermediate metastable phases Aluminum impurity in Fe-hydroxides results in lower degree of crystalinity with sluggish kinetics of crystallization of intermediate species which are more reactive towards contaminants

4. Transformation of mixed Fe-Al hydroxide nano-particles upon aging Formation of Fe-Al coatings on quartz in the lab and in the field Synthesis of Al-substituted hematite nano-particles #1 #2 #3 XRD: crystal structure (cell parameters) EXAFS: hematite structure (Fe-O, Fe-Fe, Fe-Al distances) TEM: particle morphology of particular crystal phase How Al-substitution influence the crystal structure and morphology of nano- hematite? Would these properties be different depending on the precipitation pathway? What is the structure and composition of soil coatings? How coating structure and morphology change with time? How presence of Al modify the properties of coating? XRD: qualitative mineral composition ATR-FTIR: quantitative composition How to quantitatively resolve mineral composition in the mixture? What is kinetics of mineral crystallization in mixture? GIXAS: structure of the coating (Fe-O, Fe-Fe, Fe- Al distances) GISAXS: particle morphology, distribution on the surface of particular crystal phase ProjectResearch QuestionsMethods Project overview

5. Homogeneous precipitation and transformation of mixed Fe-Al nano-particles using ATR-FTIR and XRD Research hypothesis: kinetics of crystallization of minerals (goethite and/or gibbsite) from mixed Fe-Al hydroxides is much slower than that of the pure phase due to the formation of intermediate phases that are indefinitely metastable in low-temperature soil environments. Specific objectives: (1)determine the mineral composition (percentage of goethite and gibbsite) in mixed Fe-Al hydroxides as a function of Al-substitution and reaction time, and (2)determine the effect Al-substitution may have on the rate of crystallization of the primary (Fe) precipitate. Project #1

6. [Fe+Al] = 10 -2 M; %Al: 0, 10, 25, 30, 50, 75, 100; pH = 5 Slow titration rate (0.1 ml/min) Dialysis to remove salts and excess Al Time: 0, 2, 9, 23, and 54 days, aged at 50 C Experimental conditions: Methods: nano-particle synthesis Project #1 Fe (+Al), pH ~2 0.1 M KOH

7. Methods: Infrared measurements ATR Crystal Evanescent wave 0.1 µm ATR Crystal Sample Incident radiation Reflected radiation Mirror The principle of ATR-FTIR Infrared radiation is focused onto the edge of ATR crystal, reflected through the crystal and directed to the detector. Radiation penetrate up to 0.1 µm into solution, where it is absorbed and cause the vibrations of molecule bond The infrared spectra is obtained with unique bands for each bond type Project #1

8. Methods: XRD measurements Project #1 Brookhaven National Laboratory beamline X-16C

9. Project #1 Molecular dynamic modeling: calculation of vibrational OH-frequencies 100% Fe100% Al (a) (b) (c) (d) Fe Al O H GoethiteAl-substituted goethite Isomorphous substitutionAl-clusters Gibbsite Build goethite and gibbsite models based on available experimental crystallographic data Create Al-substituted goethite and calculate new atomic coordinates Using Vienna Ab-initio Simulation Package (VASP) obtain theoretical OH- frequencies for goethite and Al-substituted goethite Use these frequencies as a reference to interpret Infrared data

10. Changes in mineral composition of mixed Fe-Al nano-particles with increasing Al-substitution. Suspensions were aged for 2 days at 50 C Preliminary work: infrared data Project #1 Dotted and solid lines (perpendicular to x-axis) show characteristic goethite and gibbsite band positions, respectively

11. 0%Al25%Al Transformation of Fe(-Al) nano-particles upon aging at 50 C. Project #1 Preliminary work: infrared data

12. Project #1 Expected results MCR analyses of high resolution ATR FTIR data will allow to de-convolute and quantify the mineral composition in complex Fe-Al hydroxides mixtures XRD data will be in good agreement with infrared data The main intermediate species that control the kinetics of crystallization will be identified

13. Project #2 The presence of aluminum in solution will change the mineral composition and coating thickness at any given time compared to aluminum free systems; Iron and aluminum migrate through the soil profile in the form of hydroxide nano-particles that accumulate in lower profiles to form coatings on sand grains; The composition and spatial distribution of different mineral phases in the coatings may reveal the mechanism of its formation. Research hypotheses Specific objectives Formation of Fe-Al coatings on a quartz substrate: laboratory and field investigations (1) Study the formation and development of coatings in situ by placing a quartz wafer into a Spodosol profile (field experiment); (2) Determine structure of the coatings as a function of Al-substitution and reaction time (lab experiment)

14. Project #2 Podzolization mechanisms Organic acids Organo-Al -(Fe) complexes Si, Al, FeAl-Fe-Si inorganic sols Fe-oxide, allophane, imogolite Microbial activity supersaturationprecipitation Addition of Al and Fe adsorption Microbial degradation of organic ligands Release of Fe and Al Fe-oxide, allophane, imogolite Flocuulation by cations: K +, Mg 2+ O E Bh Bs C pH = 4 pH = 5 Si Adsorption/precipitation theory Proto-imogolite theory Biodegradation theory

15. State College Philipsburg Milesburg 504 I-80 220 32 2 Bellefonte Black Moshannon Lake X 100 cm 4 m Time1=6 monthsTime 2 =12 monthsTime 3 =24 months Time 4=36 months 4 m 5 cm Project #2 Methods: field experiment Field layout well-polished quartz wafer semi-polished quartz wafers silica gel sand

16. Project #2 Methods: lab experiment [Fe 2+ ] = 10 -4 M pH ~ 5 [Al] = 0.2x10 -4 M [Fe 2+ ] = 10 -4 M pH ~ 5 Reaction time, hours 0.51 1.52

17. Methods: GIXAFS measurements Project #2 < 0.18 degree I1I1 I0I0 Energy Dispersive Detector – 30 element Ge X-ray fluorescence Analysis within the first nanometers from the surface Polished surface is required 30 element Ge-detector in fluorescence mode Grazing incidence angle, θ = 0.18 o Info about oxide structure: Fe coordination number ID of Fe neighboring atoms (Fe, Al or C): differentiate among Fe-O-Fe, Fe-O-Al and Fe-O-C local bonding environments

18. Methods: GISAXS measurements a non-destructive structural probe does not require a conducting surface or sample preparation (in-situ characterization possible) yields excellent sampling statistics (averages over macroscopic regions to provide information on nanometer scale) provides information on particle geometry, size distributions, spatial correlations Grazing Incidence Small angle scattering of x-ray Project #2 irradiate a sample with a well- collimated X-ray beam measure the resulting intensity as a function of angle between the incoming beam and scattered beam determine the structure that caused the observed pattern

19. Expected results Project #2 Statistically significant and steady increase in coating thickness in three years will allow to estimate the rate of coating formation in the field; Spectroscopic analysis (GIXAS) will give reasonable information of the coating structure, i.e. we should be able to distinguish between Fe-organic (Fe-O-C) bonding and Fe-O-Fe(Al) bonding in the organic-rich and organic-free horizons, respectively; Spectroscopic data will be similar for the laboratory and field samples (Bx horizon); We will be able to infer mineral composition on the coatings from our spectra; Coating structure and morphology will be different in the presence of aluminum compared to Fe-only experiments.

20. In the field: quartz wafer placed in spodosol Bx horizon and recovered after 1 year AFM image Fe K-edge EXAFS spectrum (GIXAFS) In the lab: fused silicon after 2.5 hours reaction with Fe(II) 10 -4 M solution under oxidizing conditions AFM image Fe K-edge EXAFS spectrum (GIXAFS) Project #2 Preliminary work

21. Project #3 Synthesis and characterization of Al-substituted hematite nano-particles The effect of Al-substitution in micron-size hematite particles (decrease in crystallinity and particle size) is also true for nano-size Al-substituted hematite particles; This effect is even more pronounced for nano-particles due to the higher surface to bulk ratios encountered in nano-sized particles,. The amount of aluminum incorporation into the hematite structure depends on the pathway of nano-hematite formation Research hypotheses Specific objectives Synthesize Al-substituted nano-hematite particles (less than 30 nm) following different synthesis procedures Compare particles properties (size, shape and structure) among different sets using XRD, TEM, EXAFS and chemical analyses.

22. a. Procedure #1 FeAl Fe+AlFe Al b. Procedure #2 c. Procedure #3 Methods: nano-hematite synthesis Project #3 mol%Al[Fe], M[Al], MTotal [Al+Fe], MFe:Al 00.010 0 100.0090.0010.010.1 200.0080.0020.010.3 300.0070.0030.010.4

23. EXAFS: method Fe:Al = 1:1 Fe-O Fe-Fe Fe-Al Project #3

24. Preliminary work Project #3 Particle size of hematite suspensions with different initial aluminum mol %.

25. TEM data XRD data Project #3 Preliminary work

26. Expected results Project #3 The percent of Al-substitution will be different depending on the synthesis procedure, and it will be, probably, the highest using procedure #3 (addition of Fe-chloride dropwise to Al-solution) As Al-percentage in initial solution increases, hematite particle sizes are expected to decrease; particle morphology will change from round to elongated shapes

27. Research timetable