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Hydrothermal Synthesis of Nanomaterials. Andrew van Bommel January 18 th , 2006. Hydrothermal Synthesis. The reactants are dissolved (or placed) in water or another solvent (solvothermal) in a closed vessel Bomb is heated above BP Conventional or MW oven Commercially:

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hydrothermal synthesis of nanomaterials

Hydrothermal Synthesis of Nanomaterials

Andrew van Bommel

January 18th, 2006

hydrothermal synthesis
Hydrothermal Synthesis
  • The reactants are dissolved (or placed) in water or another solvent (solvothermal) in a closed vessel
  • Bomb is heated above BP
  • Conventional or MW oven
  • Commercially:
    • Tons of zeolites daily

Nazari, G.A., Pistoria, G. Lithium Batteries; Klumer Academic Pubs.: Boston, 2004.

conditions
Conditions
  • Solvent above boiling point (supercritical water)
  • Usually basic conditions
  • Useful for Nano!
    • Oxides (TiO2, VOx, MxMnO2)
    • Layered oxides: nanowires/tubes
    • C-nanotubes can be formed this way
    • Some elemental nanostructures (eg: Bi)
mechanism for ht rxn
Mechanism for HT rxn
  • Usually follows a liquid nucleation model
  • Differs from solid-state- reaction mechanism from diffusion of atoms or ions between reactants
  • Due to enhanced solubility:
    • Solubility of water increases with temperature, but alkaline solubility increases dramatically with temperature

Barrer, R.M. Hydrothermal Chemistry of Zeolites; Academic Press: London, 1982

solubility
Solubility
  • Solubility of SiO2 (quartz)

Barrer, R.M. Hydrothermal Chemistry of Zeolites; Academic Press: London, 1982

next slides
Next Slides
  • Examples:
    • Nanoparticles
    • Nanowires/tubes
    • Nanoflowers
  • Control of Shape
batio 3 nanoparticles
BaTiO3 Nanoparticles
  • Ba(OH)2 + TiO2 BaTiO3 nanoparticles
  • 300 - 450°C, HT
  • Two proposed mechanisms:
    • Dissolution-recrystallization
    • In situ crystallization

Hakuta, R., Ura, H. Hayashi, H, and Arai, K. Ind. Eng. Chem. Res. 2005, 44, 840-846

dissolution recrystallization
Dissolution-Recrystallization
  • BaTiO3 formation at 150°C
  • Stated:
    • “when varying the water/isopropanol ratio in synthesis at 150°C, the grain size of barium titanate decreases when the amount of alcohol increases, i.e. when the solubility of the precursors decreases”
    • “TEM observations of incompletely reacted powders showed that the grains are either amorphous or entirely crystalline BaTiO3, which means that homogeneous nucleation and growth is occurring instead of heterogeneous nucleation
    • “high resolution TEM observations of fully reacted powders revealed the presence of necks between particles. These three experimental observations in the same reaction system provide strong evidence of dissolution-precipitation as the primary reaction mechanism.”

Pinceloup, R., Courtoisa, C., Vicensb, J., Lerichea, A., and Thierry, B. J. Eur. Ceram. Soc. Res. 1999, 19, 973-977.

in situ crystallization
In-situ crystallization
  • Non-dissolved TiO2 reacts with barium and hydroxide ions

Eckert, J.O., Hung-Houston, C.C., Gersten, B.L., Lencka, M.M., Riman, R.E., J. Am. Ceram. Soc. 1996, 79, 2939.

why nano
Why Nano?
  • For in-situ transformation, formation of a porous product facilitates the transfer of the reacting species, leading to a facile reaction
  • For dissolution-precipitation reaction, dissolution (and subsequent precipitation) must be fast to ensure a steady flow of reactants

Eckert, J.O., Hung-Houston, C.C., Gersten, B.L., Lencka, M.M., Riman, R.E., J. Am. Ceram. Soc. 1996, 79, 2939.

tube wire formation
Tube/wire Formation
  • TiO2 +NaOHtitanate nanomaterial
  • Crystal flakes rolled along [001] direction

Chen, Q., Du, G.H., Zhang, S., Peng, L.M. Acta Cryst. 2002, B58, 587-593.

why nanowires tubes
Why nanowires/tubes?
  • Two-dimensional crystal flakes have low resistance to bending: hydrothermal energy curls these flakes
  • Why tubes?
    • When diameter grows, the strain in the tubes is outweighed by the minimizing of energy with nanotubes’ self-closed layers (no dangling bonds)

Remskar, M. Adv. Mater. 2004, 16, 1497-1502.

more nano
More Nano!
  • Nanoflower ZnO- CTAB assisted hydrothermal reaction of ZnO (in NaOH solution)

Zhang, H., Yang, D., Ji, Y., Ma, X., Xu, J., Que, D. J. Phys. Chem. B. 2004, 108, 3955-3958

hydrothermal route
Hydrothermal Route
  • Pros:
    • New materials
    • Easy, relatively cheap
  • Cons:
    • Difficult to control morphology, size
    • Not for all materials
    • May obtain variation in size
summary
Summary
  • Hydrothermal synthesis involves the chemical reaction of materials in aqueous solution heated (usually above BP) in a sealed vessel (bomb)
  • Alkaline solution used to increase solubility (for a dissolution-precipitation reaction)
  • It is difficult to predict the resultant morphology of the product
summary16
Summary
  • Nanomaterials are apt to form in HT synthesis as the formation of these structures allows for facile diffusion of reactants
  • Hydrothermal synthesis is used for oxide nanoparticle synthesis as the solubility is high in the alkaline medium