1. Self-assembled mesoporous metal oxide thin films
Purdue University MSE REU
August 5, 2004
Heidi Springer
Advisor: Dr. Hugh Hillhouse
Vikrant Urade

2. What are mesoporous materials?
Porous materials whose pores are between 2 and 50 nm in diameter.
The mesoporous materials investigated here have uniformly ordered pores.
Silica based materials first synthesized by scientists at the Mobil Corporation in 1992.
Non-silica mesoporous materials first reported at UC Santa Barbara in 1994.

3. Applications Molecular sieves High surface area catalysts Gas sensors
Dye sensitized photovoltaic solar cells

4. Mesoporous materials are templated by amphiphilic molecules.
An amphiphillic molecule has a hydrophillic (water loving) head and a hydrophobic (water loathing) tail.
A micelle is an association of amphiphillic molecules.
Mesoporous structure is created by the ordered packing of micelles.
Courtesy of Brian Eggiman

5. Why do amphiphiles form micelles?
Gibb’s Free Energy (ΔG) is a thermodynamic quantity which predicts the spontaneity of a reaction.
A decrease in Gibb’s Free Energy indicates a spontaneous reaction.
Water molecules create structure by forming hydrogen bonds with one another.
The hydrophobic tails of individual amphiphiles placed in solution force water molecules to associate in a particular way. This decreases the entropy (ΔS) of the system.
When the hydrophobic tails associate to each other (form micelles) in order to minimize their interaction with water molecules they increase the entropy of the system.
ΔG = ΔH - TΔS
An increase in entropy, decreases Gibb’s Free Energy of the system therefore the reaction will occur spontaneously.

6. What determines micelle shape?
Diagrams compiled from work by Brian Eggiman and Soler-Illia et al, “Chemical Strategies To Design Textured Materials: from Microporous and Mesoporous Oxides to Nanonetworks and Hierarchical Structures”, Chem. Rev. 2002, 102,

7. How do we use micelles to form mesoporous metal oxides?
Courtesy of Brian Eggiman

8. Pore Structure Characterization
X-Ray Diffraction
Small angle XRD
0.6 to 3.0 degrees 2θ
Peaks in XRD pattern show d-spacing between micelles (pores) in parallel planes.
Transmission Electron Microscopy (TEM)

9. Example of silica XRD pattern indicating mesostructure

10. Research Goal
Synthesize mesoporous tin oxide thin films with ordered cubic structure.
Explore impact of surfactant concentration on mesostructure formation using amphiphilic triblock copolymers (PEO-PPO-PEO).

11. Experimental Method
Surfactant (amphiphile source) solution is mixed with metal oxide precursor.
Combined solution is deposited onto glass slides using dip coating.
As slides are withdrawn from solution, solvent evaporates leaving hybrid surfactant/metal oxide thin film.

12. Experimental Method
Samples are subjected to humidity or thermal treatments to aid structure condensation.
Samples are calcined to remove organic template leaving a uniformly structured mesoporous material.

13. Surfactant Concentration P123
Pluronic P123 (EO20PO70EO20)
Maintained consistent solution of:
5.4 grams tin (IV) chloride
5.4 grams water
41 grams ethyl alcohol.
Varied P123 content from 1.2g – 1.8g
(EO):Sn molar ratio of 0.4 – 0.6.

14. Best mesostructure observed at 1.8g P123.
P123 Results
Best mesostructure observed at 1.8g P123.
(EO):Sn molar ratio of 0.6.

15. Surfactant Concentration F127
Pluronic F127 (EO106PO70EO106)
Maintained consistent solution of:
5.4 grams tin (IV) chloride
5.4 grams water
41 grams ethyl alcohol.
Varied F127 content from grams.

16. No XRD peaks observed at lowest concentrations.
F127 Results
No XRD peaks observed at lowest concentrations.

17. F127 Results
Unresolved peaks, indicating poor mesostructure begin to appear at 1.25g F127.

18. Best structure is observed at 1.75g F127.
F127 Results
XRD patterns of mesostructured tin oxide displaying an Im3m derived structure. (a) after thermal treatment at temperatures up to 250°C and (b) after calcination at 400°C for four hours.
Courtesy of Vikrant Urade
Best structure is observed at 1.75g F127.
(EO):Sn molar ratio of 1.4.

19. F127 Results
Courtesy of Vikrant Urade

20. Future Work Expand synthesis methods to other metal oxides.
Synthesize p-type mesoporous metal oxide for dye-sensitized solar cells.

21. Acknowledgments Professor Hillhouse Vikrant Urade and Brian Eggiman
Members of the Hillhouse group
2004 MSE REU group

22. Thank You