1 / 27

A Thesis Proposal by Katya Bazilevskaya Department of Crop and Soil Sciences

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

varick
Download Presentation

A Thesis Proposal by Katya Bazilevskaya Department of Crop and Soil Sciences

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. Rationale • Low-crystalline Fe and Al hydroxides exist as colloidal (<0.1 µm size) particles in natural waters or as coatingson the soil minerals • Have strong ability to adsorb contaminants due to their high surface area and pH-dependent surface charge. 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 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)?

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

  5. Project #1 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: • determine the mineral composition (percentage of goethite and gibbsite) in mixed Fe-Al hydroxides as a function of Al-substitution and reaction time, and • determine the effect Al-substitution may have on the rate of crystallization of the primary (Fe) precipitate.

  6. Project #1 0.1 M KOH Fe (+Al), pH ~2 Methods: nano-particle synthesis Experimental conditions: • [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

  7. Project #1 ATR Crystal Methods: Infrared measurements • 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 Evanescent wave Sample 0.1 µm ATR Crystal Mirror Incident radiation Reflected radiation

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

  9. Project #1 Fe Al O H Molecular dynamic modeling: calculation of vibrational OH-frequencies Isomorphous substitution Al-clusters (b) (a) (c) (d) Goethite Al-substituted goethite Gibbsite 100% Fe 100% Al • 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. Project #1 Preliminary work: infrared data Dotted and solid lines (perpendicular to x-axis) show characteristic goethite and gibbsite band positions, respectively Changes in mineral composition of mixed Fe-Al nano-particles with increasing Al-substitution. Suspensions were aged for 2 days at 50 C

  11. Project #1 Preliminary work: infrared data 0%Al 25%Al Transformation of Fe(-Al) nano-particles upon aging at 50 C.

  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 Formation of Fe-Al coatings on a quartz substrate: laboratory and field investigations Research hypotheses • 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. Specific objectives (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 O E Bh Bs C Podzolization mechanisms Adsorption/precipitation theory Proto-imogolite theory Microbial activity Biodegradation theory Organic acids Organo-Al -(Fe) complexes Si, Al, Fe Al-Fe-Si inorganic sols pH = 4 Microbial degradation of organic ligands Release of Fe and Al adsorption Si Fe-oxide, allophane, imogolite Addition of Al and Fe Flocuulation by cations: K+, Mg2+ Fe-oxide, allophane, imogolite pH = 5 supersaturation precipitation

  15. Project #2 4 m well-polished quartz wafer semi-polished quartz wafers silica gel sand Time1=6 months Time 2 =12 months Time 3 =24 months 5 cm 100 cm 100 cm 100 cm 100 cm 4 m Methods: field experiment I-80 Milesburg 504 Black Moshannon Lake Philipsburg Bellefonte X 220 322 State College Time 4=36 months Field layout

  16. Project #2 [Fe2+] = 10-4 M pH ~ 5 [Fe2+] = 10-4 M [Al] = 0.2x10-4 M pH ~ 5 Methods: lab experiment 1.5 2 0.5 1 Reaction time, hours

  17. Project #2 Energy Dispersive Detector – 30 element Ge X-ray fluorescence I1 I0 < 0.18 degree Methods: GIXAFS measurements • 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 • Analysis within the first nanometers from the surface • Polished surface is required • 30 element Ge-detector in fluorescence mode • Grazing incidence angle, θ = 0.18o

  18. Project #2 Methods: GISAXS measurements Grazing Incidence Small angle scattering of x-ray • 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 • 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. Project #2 Expected results • 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. Project #2 Preliminary work In the field: quartz wafer placed in spodosol Bx horizon and recovered after 1 year Fe K-edge EXAFS spectrum (GIXAFS) AFM image In the lab: fused silicon after 2.5 hours reaction with Fe(II) 10-4 M solution under oxidizing conditions Fe K-edge AFM image EXAFS spectrum (GIXAFS)

  21. Project #3 Synthesis and characterization of Al-substituted hematite nano-particles Research hypotheses • 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 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. Project #3 Fe Al Fe+Al Fe Al a. Procedure #1 c. Procedure #3 b. Procedure #2 Methods: nano-hematite synthesis

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

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

  25. Project #3 Preliminary work TEM data XRD data

  26. Project #3 Expected results • 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

More Related