Lecture 18 Nanominerals

Perturbation of Interfacial Water Perturbation of Interfacial Water
MD Simulation of Water near Hematite Nanoparticles
• Ordering of water, the intermolecular bonding, and water exchange rates are affected by nanoparticle size and morphology and morphology
γ ≡ (δG / δA)P ,T
G = Gibbs Free Energy, A = surface area • The total free energy of a system then is: gy y Gtot = ∑ μi ni + ∑ γ j A j
i j
Thermodynamic y Properties
Buseck and Posfai (1999) PNAS 96, 3372‐3379 Buseck et al. (2000) Int. Geol. Rev. 42, 577‐593
Unique Aspects of Nanoparticles Unique Aspects of Nanoparticles
Fig. 7. Progression of chain development: (a) single primary crystallite; (b) f i t llit four primary crystallites f i t llit forming i a single crystal via oriented attachment; (c) five primary crystallites forming a single crystal via oriented attachment; (d) single crystal of anatase with magnified inset of the attachment interfaces.
Burns et al. (2005) Angew. Chem. Int. Ed. 44, 2135‐2139
Small Angle X‐ray Scattering (SAXS)
Small‐Angle Scattering g g
Svergun and Koch (2003) Rep. Prog. Phys. 66, 1735–1782
Repulsive Force Depends on Double Layer Thickness, Which Depends on I h k h h d
• Critical Coagulation Concentration (CCC): Ionic strength above which particles aggregate
1 3
1
Figure 10. TEM micrographs of aggregates formed by counterion screening of surface charge. KCl concentration is 39 mmol kg-1.
3 4 2
2
4
Figure 5. Summary of kinetic data. Hydrodynamic diameter of hematite particles after 30 rain coagulation time as a function of (a) KCl and (b) phosphate concentrations. Hematite concentration = 10 mg L-1, pH = 6.0, T = 25°C
General Particle Aggregation Behavior General Particle Aggregation Behavior
Particle Aggregate Structure Affected by Surface Charge, Electrolytes, and Adsorbates Ch El l d Ad b
Chorover et al. (1997) Clays Clay Miner. 45, 690‐708
Oriented Aggregation of Nanoparticles: TiO2 l
Penn and Banfield (1998) Science 281, 969‐971 Penn and Banfield (1999) GCA 63, 1549‐ 1557
Surface Thermodynamics Surface Thermodynamics
• Surfaces contribute to the free energy of a Surfaces contribute to the free energy of a system • This is described by the surface free energy: This is described by the surface free energy:
Surface Restructuring Surface Restructuring
Zhang et al. (2003) Nature 424, 1025‐1029
Domains or Stacking Faults Domains or Stacking Faults
Zhang and Banfield (2009) J. Phys. Chem. C 113, 9681‐9687
Lecture 18: Nanominerals Lecture 18: Байду номын сангаасanominerals
Size Range of Natural Particles Size Range of Natural Particles
Fig. 2. Examples of how ferric iron occurs in the environment, ranging from the molecular to macroscopic scales. (Left) Molecular ferric oxide states, including an octahedrally coordinated monomer [hexaquairon III (53), top] and oligomer [trimer cluster (54), bottom] with Fe3+ (smaller dark red spheres), oxygen (larger light red spheres), and hydrogen (light pink spheres). These molecules are hydrogen‐terminated but should only be considered approximations of actual aqueous/environmental states. (Middle) Polyhedral representations of 1‐ and 5‐nm hematite (Fe2O3) nanoparticles. Each polyhedron represents an Fe3+ in octahedral coordination with oxygen. The thickness of the 5‐nm particle should be typically several (roughly five to seven) octahedral layers (23) and that of the 1‐nm particle should be just a few octahedral layers. (Right) (Top) typically several (roughly five to seven) octahedral layers (23) and that of the 1 nm particle should be just a few octahedral layers (Right) (Top) HRTEM image of hematite nanoparticles from Namibia (Africa) (sample courtesy of the Smithsonian Institution research collection); (Middle) TEM image of an unoriented aggregate of 3‐ to 5‐nm hematite crystals (stippled portion of the image) from an acid mine drainage site in Montana (USA) (55); (Bottom) photograph of macroscopic specular hematite (courtesy of R. Lavinsky). (from: Hochella et al. (2008) Science)
Spagnoli et al. (2009) GCA 73, 4023–4033
Surface Functional Group Reactivity G R i i
Rustad and Felmy (2005) GCA 69, 1405–1411
Nanoparticle Aggregation Nanoparticle Aggregation
Nuclear Test Site Groundwater
Utsunomiya et al. (2009) ES&T 43, 1293‐1298