Preparation of Ordered Mesoporous Silicas using NonIonic Block Copolymeric Surfactants

1
Preparation of Ordered Mesoporous Silicas using
Non-Ionic Block Copolymeric Surfactants

• Mandelle Danser
• A. Y. Fadeev

2
Outline

• Introduction
• Procedure
• Data/Results
• Future Work
• References
• Acknowledgements

3
Introduction

• Ordered mesoporous silica structures,
  specifically SBA-15 can be formed with the
  synthesis of various copolymer surfactants.
• Different copolymers have different molecular
  weights which lead to changes in the SBA species
  formed.

4
Introduction

• Studies have found that, in addition to changing
  molecular weight, the radius of the pores can be
  altered by changing the temperature and duration
  of the reaction.
• The solids recovered are analyzed by various
  techniques including thermogravimetric analysis
  and infrared spectroscopy.

5
Procedure

• 4.0 grams of the block copolymer (Pluronic P103,
  L121, and L64) are combined with 30.0 mL of water
  and 107.0 mL of 2.0M HCl (pHlt 1) while stirring
  at 35.0C.

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Structures of Copolymer Surfactants
EO ethylene oxide (CH2-CH2-O)n PO propylene
oxide (CH2)2-CH-On
Pluronic P103 Molecular Weight 4950
g/mol EO17PO56EO17
Pluronic L121 Molecular Weight 4400
g/mol EO5PO70EO5
Pluronic L64 Molecular Weight 2900
g/mol EO13PO30EO13
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Procedure

• 9.1 mL of TEOS (Tetraethoxysilane) is then added
  while the mixture continues to stir.
• This stirs for 20 hours at 35.0C.
• Stirring is halted after 20 hours, and the
  temperature is raised to 80.0C and left
  overnight.
• The solid is then filtered, washed, and allowed
  to air dry.
• The solid is calcinated from room temperature to
  500.0C and held at this temperature for 6 hours.

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SBA-15
Courtesy of www.quanta.kyutech.ac.jp/
deguchi/study2.htm
9
Thermogravimetric Analysis (TGA)

• A small amount of sample is placed on a pan.
• The sample is placed into a compartment where the
  temperature is controlled by a computer.
• The weight change of the sample is compared to
  original weight taken, and a graph is constructed
  which illustrates the change.

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TGA results of various surfactants
Calcinated P123
L64
P103
L121
Elemental Analysis showed .3 carbon left after
calcination
11
Infrared Spectroscopy

• Infrared spectroscopy involves the absorption of
  infrared light causing chemical bonds to bend and
  stretch.

• The atoms in a molecule are constantly
  oscillating around average positions. Bond
  lengths and bond angles are continuously changing
  due to this vibration.

• A molecule absorbs infrared radiation when the
  vibration of the atoms in the molecule produces
  an oscillating electric field with the same
  frequency as the frequency of incident IR
  "light". The molecule must exhibit a dipole
  moment.

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The Block Diagram for an Infrared Spectrometer
Courtesy of http//scienceworld.wolfram.com/physic
s/FourierTransformSpectrometer.html
13
Analyzing IR Spectra

• The bands that appear in the spectrum depend on
  the types of bonds and the structure of the
  molecule.

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Band similarities between different SBA species
3745
Isolated SiOH
3446
P103
Water
3660
Hydrogen bonded SiOH
Bare Silica (Prodigy)
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Shift in Bands With Temperature Increase of P103

Isolated SiOH peak for 25 C
3737
3432
Isolated SiOH peak for 500 C
Water band at 25 C

3746
Water band at 150 C
Water band at 302 C
Water band at 400 C
Water band at 500 C
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Shift in Bands With Cooling of P103
3737
Isolated SiOH peak for 500 C
3746
Isolated SiOH peak for 25 C
17
Shift of SiOH Band With Increase in Temperature
in P103
210 C
100 C
25 C
56 C
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Cooling of SiOH Band in P103
500 C
300 C
200 C
100 C
23 C

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The Effect of Temperature on IR spectra of Silica

• As temperature increases the isolated SiOH band
  shifts to the right. As the system is cooled,
  the band returns to original positioning.

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The Effect of Temperature on IR spectra of Silica

• As hydroxyl groups are removed from the silica
  surface, there are fewer sites for water
  absorption present.
• At 400C rehydration and dehydration can occur
  simultaneously.
• As temperature increases above 400C, there is a
  decrease in water absorption.
• At 800C water can no longer be added and the
  dehydration process is irreversible.

21
The Effect of Temperature on IR spectra of Silica
Hair, M.L. Hydroxyl Groups on Silica Surface.
Journal of Non-Cyrstalline Solids 19 (1975) 302
22
Future Work

• The use of the spectrum to determine the
  concentration of the hydroxyl groups.
• The use of TGA to determine the concentration of
  the hydroxyl groups.

23
References

• Hair, M.L. Hydroxyl Groups on Silica Surface.
  Journal of Non-Cyrstalline Solids 19 (1975)
  299-309.
• Zhao, Dongyuan. Nonionic Triblock and Star
  Diblock Copolymer and Oligomeric Surfactant
  Syntheses of Highly Ordered, Hydrothermally
  Stable, Mesoporous Silica Structures. Journal of
  American Chemical Society 120 (1998) 6024-6036.
• Picture of SBA-15 ltwww.quanta.kyutech.ac.jp/
  deguchi/study2.htmgt
• Fourier Transform Spectrometer lthttp//scienceworl
  d.wolfram.com/physics/FourierTransformSpectrometer
  .htmlgt

24
Acknowledgements

• Dr. Fadeev
• Sue DAndrea
• Roy Helmy
• My favorite Physical Chemistry Lab Group
  especially Megan Kouba. For the rest of the
  group see Megans Acknowledgements
• Dr. Murphy