Just basics of mesoporous materials!!The Break through came around 1992 by both Japanese and Mobil scientist on the soft template based synthesis of mesoporous materials

1. Mesoporous Materials – Synthesis
and Applications
Vijaykumar S.Marakatti,
PPISR, Bangalore.

2. Outline of the talk
 Introduction to porous materials
 Classification of porous materials
 Synthesis mechanism of mesoporous materials
 Applications of mesoporous materials

3. Introduction
“the overwhelming tendency for solids to minimize void space
within their structure” is inherent , porous materials are difficult
to make naturally.
But Einstein say “ in the middle of difficulty lies opportunity”
The above statement was made true by the Mobil scientist in the
year of 1992 by successfully synthesizing the Mesoporous
materials (MCM-41 and MCM-48) by using soft template
strategy.
This opened a new area of materials called Mesoporous
materials, and still lot of work are fascinating in this field.

4. What are Porous materials
 Most generalized definition of porous materials is continuous and
solid network material filled through voids.
 A material can be recognized as porous if its
internal voids can be filled with gases.
The history of porous materials began with the zeolites having
aluminoisilicates framework which was synthesized by the use single
template molecule with small pore.

5. Classification of porous materials
Depending on pore size Depending on building
framework
Micropoorus Mesoporous Macroporous
<2nm 2-50 nm >50nm
ZSM-5 MCM-41 Sponge
Purely inorganic Organic Inorganic Purely
hybrid organic
Silica MOF organic
porous polymers

6. Mesoporus Materials
 Meso a Greek prefix – “ in between ” - micro and macro
porous system
 Mesoporous materials may be ordered or disordered.
They possess high
 Surface area -400 -1000 m2/g
 Large pore volume
 High stability -500 -600 °C
 They are usually synthesized by the use of Soft template
method.
Ex: MCM-41,SBA-15,FDU-11,IITM-56 etc.

7. Difference between the zeolites and mesoporous materials
Zeolites Mesoporous Materials
Highly crystalline Periodic arrangement with amorphous in
nature
TO4 networks TO4,TO5 and TO6 networks
Si and Al are four connected by covalent Si and Al are 2 or three connected ,more
bond, less surface hydroxyl groups surface hydroxyl groups
Hydrophobic surface area Hydrophilic surface area
High hydrothermal stability Less hydrothermal stability
Crystalline walls and are thick Amorphous walls and are thin
Synthesis temp is high (80 – 300 °C) Synthesis temp is low (-10 to 120°C)
Long crystallization time Formation rates are fast
Aqueous media is required for Non –aqueous solvents and non polar
crystallization solvents can be used
Synthesis of zeolite is carried out in Synthesis pH rang is from 0 to 12
neutral /weakly acid media

8. Synthesis of mesoporous materials
Soft template (endo template) Hard template (exo template, nano casting)
• Uses soft templates like organic •Uses inorganic materials like silica, carbon
etc
molecules .
•Tedious work up, hard to get good
morphology and costly
•Good shape , Size and morphology. CMK-1
simple
• SBA-15 ,MCM-41 etc
Meso-silica
CMK-1

9. Synthesis of mesoporous materials using soft
template strategy
1. Surfactants.
2. Formation of Micelles.
3. Inorganic precursor .
4. Interaction of Micelles with inorganic precursor.
5. Hydrothermal treatment followed by separation and drying
6. Removal of template.
7. Proposed mechanism
8. Characterization of material.

10. 1. Surfactant/ Template/Structure directing agent.
 Large organic molecules(High molecular weight) with both
hydrophilic and hydrophobic groups.
 Depending upon charge they can be
classified as
Cationic Anionic Non ionic/neutral
•Excellent solubility •Excellent solubility •Excellent solubility
•High critical Micelle con. • repulsion between the • High critical micelle temp.
•acidic and basic media anionic surfactant is more. •Acidic / basic media
• toxic and expensive • non-toxic and cheap

11. 2. Formation of micelle
• At a Low surfactant concentration will favor
arrangement on the surface.
• As the concentration increases surface being more
crowded as result molecule arrange in to micelles.
• At certain concentration the surface is completely
loaded and any further addition leads to the
Micelle arrengment.This conc. is known as CMC.
• Beyond the CMC self assembly of micelle occurs to
from 3D and 2D rod like arrays.
• Different template have the different CMC.
• To get ordered materials – 0 to20 mg/L

12. Different type of surfactant arrangement

13. What Makes them to show different type of arrangements ?
1. Critical micelle concentration
Low micelle conc. are good to get ordered materials.
2. Packing parameter (g)
g = V / ao l
V=Total volume of surfactant hydrophobic chains+ co-solvnet.
ao= Effective hydrophilic head group area at the aq. micelle surface.
l = kinetic surfactant tail length.
g <1/3 = cubic and 3 D hexagonal,
1/3<g>1/2 = 2D hexagonal
1/2<g>2/3 = cubic
g=1 = Lamellar
3. The hydrophilic and hydrophobic Volume ratio (VH/VL)

14. 3.Inorganic precursor and pH
Inorganic Precursor silica depends upon pH
Basic synthesis (pH =9.5 to 12.5)
-Polymerization and cross Linkage of silicate species are reversible
Silica gel, colloidal sol, Water glass , TEOS etc.
Acidic synthesis(pH= 1 to 2 )
- Irreversible.
- Slow hydrolysis TEOS is preferred.

15. 4. Interaction of Micelles with inorganic precursor.
 Direct interaction of Surfactant with inorganic precursor
Basic -Medium Acidic-Medium

16. Interaction of Surfactant with inorganic precursor through
intermediate ions
Acidic-Medium Basic -Medium

17. Interaction of non ionic Surfactant with inorganic precursor
through intermediate ions.
Hydrogen bonds favors most of times

18. 5. Hydrothermal treatment followed by separation and
drying.
 Method to improve mesoscopic regularity's of products.
 Reorganization, growth and crystallization
 80 -150 °C is temperature is usually used.
 High temperature will lead to the disorder and decomposition of
surfactants.
 Separation – filtration or centrifugation.
 Washing –alcohol or water. Basic media needs through washing.
 Drying at room temperature is good.

19. 6. Removal of template.
 Removal of template will give rise to mesoporosity
Different ways by which template can be
removed
Light irradiation
Calcination
•Slow heating rate. Solvent Extraction • Microwave
• N2 -1 hr • Solvent ethanol /THF •Ultraviolet rays
O2- 4-6 hr – 2 °C/min • small HCl is added O3 and O
• O2-1 °C/min • Surfactant can be reused
• No surfactant recover
• low Surface silanol groups
• Not good for low thermal
stable materials
•P-123 -550 °C
• CTAB -350 °C

20. p6mm
Ia3d,
SBA-15 MCM-48 Pm3n
SBA-1 and 6
Fd3m
Im3m SBA-16 Fm3m.
FDU-2
KIT-5

21. Proposed mechanisms for synthesis mesoporous materials
1. Silicate rod assembly
 2 or 3 monolayer's of silicates species first deposits on isolated surfactant
miceller rods

22. 2. Cooperative self assembly
 Low concentration Surfactant

23. 3. True liquid crystal templating route
 High concentration Surfactant

24. Complete synthesis summary

25. 7. Characterization of mesoporous materials
1. Low angel XRD
0.5 -5 -2theta
- orederness / disorder.
2. N2 sorption measurements –BJH
method
 Surface area/pore diameter /pore
volume
3. TEM images
Order ,Morphohology ,
Wall thickness

26. Applications

27. Application Chemical Catalysis
1. Mesoporous Materials as catalyst
Al-MCM-41 ,B-MCM-41, Sn-SBA-15 - Acidic
K- AlMCM-41 , Cs-AlMCM-41 -basic
TiMCM-41 ,V-MCM-41 -Redox

28. 2.Mesoporous Materials as catalyst support
• Noble metal supported catalyst supports
Au-McM-41 , Pt- CMK-3
• Metal oxide supported catalysis
Fe2O3- MCM-41 ,RuO2-SBA-15
• Metal complex supported catalysts
Mn-Salen –SBA-15

29. 3. Application in environmental catalysis
Immobilization of enzyme on Mesoporous Materials as
catalysts
 Enzymes are excellent biocatalysts with high selectivity and efficiency
 in environment field, chemical and pharmaceutical industries
 are limited by their poor stability and chemical sensitivity

30. 4. Good adsorbents

31. 5.Applications in Biomedical field

32. 1) Sustained Drug Release System
Virtually any drug within a size range compatible with the size of the meso-
channels has potential to be encapsulated and further deliver intracellularly.
M. Vallet-Regi, et al. “A New Property of MCM-41: Drug Delivery System”, Chem. Mater. 2001, 13, 308-311.

33. 2. Mesoporous Materials for Bone Tissue Engineering

34. Mesoporous Bioactive scaffolds
Scaffolds are needed that can act as temporary templates for bone regeneration
and actively stimulate vascularized bone growth so that bone grafting is no
longer necessary.
Bioactive glass is an ideal material because it rapidly bonds to bone and
degrades over time, releasing soluble silica and calcium ions that are thought to
stimulate osteoprogenitor cells.

35. 1 Day
3 Day
7 Day

36. 6.Mesoporous Polymers

37. Pioneers in Mesoporous Materials
Galen Stucky
SBA-15
Fudan
university
FDU-11
Ryong Ryoo
KIT -6
Hard template
CMK materials
P.Selvum
IITM-56, NCCR-56

38. References:
“On the Controllable Soft-Templating Approach to Mesoporous Silicates”
Ying Wan and Dongyuan Zhao, chemical reviews, Volume 107, Number 7 .
“Soft templating strategies for the synthesis of mesoporous materials: Inorganic,
organic–inorganic hybrid and purely organic solids”
Nabanita Pal, Asim Bhaumik, Advances in Colloid and Interface Science 189–190 (2013) 21–41
Thank you